Category Archives: General Horticulture/Weeds

Vegetable Varieties for Containers

Growing plants in containers (referred to as container gardening) is an easy way to grow and maintain vegetables.  Vegetables grown in containers can easily fit on a window sill, balcony, deck, door step or any other place where space is limited but where environmental conditions are suitable for vegetable production.

The list below contains recommendations on varieties of popular vegetables that are well-suited for growing in containers.

Click the vegetable names to expand the panel and view the variety info. The panel expands downward.

To close the expanded panel, click the vegetable name below it.

In addition to the vegetables listed above, most varieties of herbs and salad greens are perfectly suitable for containers.

For more information on vegetable varieties for containers and container gardening in general:  See Extension Bulletin A3382, Container Gardening, or contact your county Extension agent.

Poison Ivy

What is poison ivy?   Poison Ivy (Toxicodendron radicans), is a perennial woody plant that grows as either a low shrub or a climbing vine.  Poison ivy is native to North America and is common in Wisconsin, growing in pastures, roadside ditches, fence rows, wooded forests, beaches and parks.  CONTACT WITH POISON IVY CAN LEAD TO SKIN RASHES, SKIN BLISTERS OR OTHER ALLERGIC REACTIONS.

Young poison ivy leaves (left) can have smooth margins, while mature poison ivy leaves (right) often have serrated or lobed leaf margins.
Young poison ivy leaves (left) can have smooth margins, while mature poison ivy leaves (right) often have serrated or lobed leaf margins.

What does poison ivy look like?  Poison ivy has alternate leaves, and each leaf has three leaflets.  The middle leaflet has a short stalk and is larger than the two other leaflets.  Leaflets are variable in shape but are typically oval with pointed tips.  The margins (edges) of leaflets can be smooth, serrated (i.e., resemble a saw blade) or lobed.  In late summer, poison ivy produces clusters of whitish berries.  These berries are eaten by birds, and the seeds inside are spread through bird droppings.

Other common plants can be confused with poison ivy.  These plants and the characteristics that distinguish them from poison ivy are outlined in the table below.

Look Alike Species How to Distinguish from Poison Ivy
Boxelder (seedlings) Opposite branching; 3+ leaflets per leaf
Ash (seedlings) Opposite branching; 3+ leaflets per leaf
Virginia creeper 5 leaflets per leaf (newly emerged leaves may have fewer)
Wild sarsaparilla 3 leaves at the top of stem; each leaf with 3-7 leaflets
Raspberry/blackberry 3+ leaflets per leaf; spiny stems
Clematis/virgin’s bower Opposite branching; side leaflets with obvious stalks
Hog peanut Leaves without teeth or lobes; weak stemmed
Jack-in-the pulpit Leaves with 3 leaflets; leaflets all stalkless
Wild strawberry Leaves with 3 leaflets; leaflets all stalkless

Why is poison ivy a problem?  All parts of poison ivy plants (including leaves, stems and roots) produce a resinous oil called urushiol that can cause severe itching, inflammation and blistering.  The oil can be spread by anything that comes in contact with poison ivy including garden tools, clothing, boots or pets.  Urushiol is present not only in living poison ivy plants but can remain active in dead plants for up to two years.  Skin sensitivity to poison ivy can vary from person to person.  If you burn poison ivy, the vaporized oil that is released can cause severe systemic allergic reactions if inhaled.

How do I avoid or reduce problems associated with poison ivy?  LEARN HOW TO IDENTIFY POISON IVY AND AVOID CONTACT WITH THE PLANT WHENEVER POSSIBLE.  If you will be working in an area where poison ivy is likely to grow, wear long pants with boots, a long-sleeved shirt and gloves to help reduce exposure.  In addition, you may want to use a poison ivy preventative lotion that can provide additional protection.  After working in a poison ivy-infested area, carefully remove and wash your clothing with hot, soapy water.  Use sanitary wipes to clean gardening tools or other items that may have come in contact with poison ivy plants.

If you believe you have come in contact with poison ivy, immediately wash any potentially exposed skin with regular soap under cold, running water.  Avoid using complexion soaps as these types of soaps tend to spread urushiol on the skin and can make the problem worse.  Poison ivy cleansing products (e.g., Tecnu skin cleanser) can help remove urushiol from skin if used within four to eight hours of exposure.  Magnesium sulfate containing skin products (e.g., Dr. West’s Poison Ivy Wash) can also help to detoxify urushiol and ease itching.  If you believe you have inhaled urushiol vapor, IMMEDIATELY contact a physician for advice.

If you believe your pet has been exposed to poison ivy, immediately bathe them using a pet-safe shampoo to remove urushiol residues.

How can I control poison ivy?

Herbicides containing the active ingredients glyphosate and triclopyr are effective in controlling poison ivy if used according to the label directions.  Use foliar sprays to spot treat shrub-form poison ivy plants or vining poison ivy growing on inert objects (e.g., fences), but only apply treatments after leaves are fully expanded and plants are actively growing (i.e., summer and early fall).  DO NOT apply foliar sprays to poison ivy growing on trees and shrubs, as the herbicide may damage these supporting plants.  Alternatively, at any time of the year, cut poison ivy stems near the soil surface and paint the stumps with a more concentrated herbicide formulation.  Be sure to read the instructions on the label of whichever herbicide you select for details on how to use the product in the safest and most effective manner possible.

When removing poison ivy plants, collect all of the above ground plant parts.  Also, be sure to rake the ground to collect any leftover poison ivy berries, leaves, stems and roots.  DO NOT burn or compost any of these materials.  Instead, bag and dispose of them in your municipal garbage.  After you remove plants and debris, spread four to six inches of clean wood chip mulch over the site to prevent possible exposures to urushiol that may remain on or in the soil.

For more information on poison ivy:  Contact your county Extension agent.

Using Wood Ash in the Home Garden

Using wood ash in home gardens can increase soil fertility and raise soil pH.
Using wood ash in home gardens can increase soil fertility and raise soil pH.

Home gardeners often ask if wood ash can be used as a fertilizer in vegetable gardens and flowerbeds, around landscape trees and shrubs, and on lawns.  Wood ash can be a valuable source of certain nutrients and can also be used to modify soil pH.  However, it needs to come from an appropriate source and its use should be based on recommendations from soil fertility testing provided by a professional lab such as the UW Soil and Forage Lab (

What are the potential benefits of using wood ash?  Wood ash contains nutrients that can be beneficial for plant growth.  Calcium is the plant nutrient most commonly found in wood ash and may comprise 20% or more of its content.  Potassium (also called potash) is another common component of wood ash, occurring at concentrations of up to 5%.  Magnesium, phosphorus and sulfur are also typically found in wood ash at concentrations of up to 2%.  Finally, wood ash can contain trace amounts of iron, aluminum, manganese, zinc, boron and other nutrients needed by plants.

In addition to its nutrient content, wood ash can help in neutralizing soil acidity.  When wood is burned, high amounts of carbonates are produced.  Carbonates react with and neutralize acid in the soil, causing the soil pH to increase.  The levels of carbonates present in wood ash (and thus its acid-neutralizing properties) will vary depending on the type of wood burned and how the wood was burned.  In general, wood ash has about 50% less acid-neutralizing capacity than commercially available acid neutralizers such as pelletized lime or aglime.  Approximately four cups of wood ash can be substituted for one pound of aglime.

What are potential downsides of using wood ash?  On occasion, even the best wood ash may contain heavy metals such as cadmium and lead, but the levels of these metals can be minimized by carefully selecting the wood that is burned to produce the ash (see below for details).  In addition, the increase in soil pH associated with using wood ash tends to decrease the likelihood of plants taking up heavy metals.  If wood ash is used at recommended rates, concentrations of heavy metals should be low enough not to pose a threat to plants, or to animals or humans who eat plants grown in treated areas.  If you are concerned about heavy metals in your wood ash, consider testing for these elements prior to use.  The UW Soil and Forage Lab (mentioned above) does not test for heavy metals at this time; however staff can help answer questions about heavy metal contaminants.

Because using wood ash tends to increase soil pH, applying it where acid-loving plants (e.g., blueberries, azaleas/rhododendrons, birch trees, red maples, pin oaks) are growing will likely not be beneficial.  Using wood ash may actually be detrimental and contribute to problems with chlorosis [see University of Wisconsin Gardens Facts XHT1002 (Chlorosis),, for details].  In addition, many vegetables and other landscape plants prefer slightly acidic soils, so wood ash should be used judiciously when growing these plants.  Finally, in some cases, increased pH due to use of wood ash may promote certain diseases.  As an example, potatoes grown at higher pH tend to be more prone to potato scab [see University of Wisconsin Gardens Facts XHT1117 (Potato Scab), available at, for details].

In order to use wood ash in the best manner possible, always make applications to garden soils based on the plants that are to be grown and based on recommendations from a certified soil testing lab.

What type of wood ash should I use?  If you decide that using wood ash is appropriate for your gardening needs, only use wood ash that has come from trees grown in natural areas.  DO NOT use wood ash produced from trees grown near industrial sites, in soils that may be contaminated with toxins or heavy metals, or if you have no knowledge of the origin of the wood that you are burning.  Also, DO NOT use ash produced by burning treated wood, waste oil, plastics or garbage.

How do I apply wood ash?  Prior to use, sift wood ash to remove large charcoal pieces, as well as any active embers.  Apply only the amount of wood ash recommended based on a soil fertility test and based on the nutrient needs of the plants that you intend to grow in the treated area.  Applying excessive amounts can lead to nutrient toxicity and/or nutrient deficiency issues in plants.  Applications of wood ash are generally limited to a maximum of 15 to 20 pounds (approximately a five gallon pail) per 1000 sq. ft., per year.  Spread wood ash evenly over the area to be treated (e.g., vegetable garden bed, established perennial flowerbed, lawn or other landscape area) during the winter.  Because wood ash particles are very fine and can easily be blown by the wind, avoid making applications when it is windy.  Whenever possible, apply wood ash to moist soil.  Where feasible (e.g., in a vegetable garden), work the ash into the soil using a rototiller, spade or rake in early spring.

Due to its alkalinity, wood ash can potentially pose a human health risk.  Therefore, when working with it, be sure to wear appropriate protective clothing (e.g., long pants, long sleeve shirt, gloves, eye goggles, dust mask) to limit exposures that might lead to skin, eye or respiratory irritation.

For more information on using wood ash in the home garden, as well as soil fertility testing:  Contact your county Extension agent.

Bagging Apples for Insect and Disease Control

Producing high quality apples in home gardens can be challenging due to damage caused by insects (e.g., apple maggot, codling moth, plum curculio, stinkbugs) and fungal diseases (e.g., apple scab, cedar-apple rust, flyspeck, sooty blotch).  Many insects damage apples when they lay their eggs in developing fruit.  Insect larvae can cause

Bagging apples can reduce fruit damage due to insects and diseases. (Photo courtesy of Janet van Zoeren)
Bagging apples can reduce fruit damage due to insects and diseases. (Photo courtesy of Janet van Zoeren)

additional damage as they tunnel into the fruit.  Wind-borne fungal spores can land on fruit leading to infections that damage fruit, reduce fruit aesthetics or affect long-term storage.

Although insecticide and fungicide sprays can help control insect pests and diseases, regular spraying can be inconvenient and costly for homeowners.  A non-pesticide alternative for protecting fruit is to encase apples in bags that provide protective barriers against insects and fungal pathogens.

What do I need to bag my apples?  First, you will need some sort of bagging material.  This could be a household plastic or paper bag, or a commercially-produced bag designed specifically for apple bagging.  Perhaps the most convenient choice is a common plastic sandwich or quart-size zip-type bag.  Zip-type bags are effective, weather proof, economical, and readily available.  You will also need something (e.g., a twist tie, tape, string, staples) to secure the bags to your apples and a pair of scissors to cut a drainage hole in each bag.

When do I bag my apples?  Start bagging when fruits are approximately ½ to 3/4 inch in diameter.  Apples typically reach this size approximately two weeks after petal fall.  Thin each cluster of apples to a single fruit, keeping the largest, best-shaped fruit in the cluster.  Make sure that the apples you select have not already been damaged.  In particular, plum curculio can damage fruit and codling moth can lay eggs before fruit are large enough to bag.  You may want to consider using an insecticide spray between petal fall and bagging to prevent this early damage.

How do I bag my apples?  Place an apple in the bag of your choice with the top of the bag around the stem.  Carefully secure the bag with a twist tie, tape, string or staple without damaging the stem.  If using a zip-type bag, place the stem in the middle and close the seal to within one inch of the stem on each side.  Staple the bag on each side of the stem to ensure that the bag will remain secure all summer.

Use scissors to cut approximately one-half inch from one of the bottom corners of the bag. This will allow condensation that may form inside the bag to drain.

Leave plastic bags on all summer.  Paper bags may deteriorate and need replacement if there is excessive rain during the growing season.  In addition, paper bags should be removed a few weeks prior to harvest to allow proper fruit color to develop.

Bagging apples can help prevent damage due to insect pests such as codling moth (left) and diseases such as apple scab (right). (Photos courtesy of Christelle Guédot and the UW-Plant Disease Diagnostics Clinic).
Bagging apples can help prevent damage due to insect pests such as codling moth (left) and diseases such as apple scab (right). (Photos courtesy of Christelle Guédot and the UW-Plant Disease Diagnostics Clinic).

What should my apples look like after they have been bagged?  Because bags prevent insects and fungal spores from reaching fruit, most of your bagged apples should be in near perfect condition.  Fruit that you do not bag will likely be blemished from insects and disease.  Blemished fruits should be removed (whether they fall to the ground or remain attached to your tree) and destroyed by burning (where allowed), deep burying or hot composting.  Diseased leaves from your apple tree should be treated similarly once they fall from the tree in the autumn.  Properly disposing of blemished fruits and diseased leaves will help limit overwintering of insect pests and disease-causing organisms, thus reducing insect and disease problems the following growing season.

For more information on bagging apples for insect and disease control:  Contact your county Extension agent.

Improving Cranberry Pollination

Successful cranberry production relies on cranberry flowers being adequately pollinated.  This fact sheet discusses several strategies that can be used to optimize pollination.

Proper pollination is important for successful cranberry production. (Photo courtesy of Johnston's Cranberry Marsh & Muskoka Lakes Winery, Ontario, Canada).
Proper pollination is important for successful cranberry production. (Photo courtesy of Johnston’s Cranberry Marsh & Muskoka Lakes Winery, Ontario, Canada).

Increase and diversify plants attractive to pollinators.  Having both native pollinators and honeybees on your marsh serves as an “insurance policy” to promote good fruit set.  Providing diverse sources of nectar and pollen (e.g., through the use of a pollinator garden), will encourage native pollinators to establish themselves long-term near your marsh and improve the health of honeybee colonies.  When planning a pollinator garden, select a site that is sunny and 1/3 to one mile away from your marsh.  Some common native plants to consider for a pollinator garden are listed in the figure below, with their approximate bloom times.

Promote nesting habitats for wild bees.  Wild bees need places to build their nests.  Approximately 70% of native bees nest underground and need areas of bare, sandy or loamy soil to build their nests.  The remaining 30% build nests by tunneling into stumps or twigs, or by constructing nests in cavities (e.g., in mounds of tall grasses, in debris piles, or in deserted rodent nests).  Native pollinators typically travel from 1/8 to one mile from their nests to feed, so suitable nesting areas need to be within this distance of a marsh for the bees to contribute to cranberry pollination.

Several programs can assist with the costs of creating pollinator habitats.  These include the USDA Environmental Quality Incentives Program, the USDA Farm Service Agency, the Wisconsin DNR Land Owner Incentive Program and the Bayer Crop Science Feed a Bee Initiative.


LEFT: Approximate bloom times for plants that are recommended to be grown near cranberry marshes as a supplemental nectar and pollen source for cranberry pollinators. RIGHT: Approximate flight periods for major groups of bees (including native species) found in cranberry marshes. The pink columns in both graphs represent the approximate time of cranberry bloom.
LEFT: Approximate bloom times for plants that are recommended to be grown near cranberry marshes as a supplemental nectar and pollen source for cranberry pollinators. RIGHT: Approximate flight periods for major groups of bees (including native species) found in cranberry marshes. The pink columns in both graphs represent the approximate time of cranberry bloom.

Reduce pesticide exposureYou can optimize bee health by creating a pollinator protection plan that promotes:

  • Practicing integrated pest management (IPM). IPM, which involves monitoring for pests and using a variety of appropriate management strategies, is used by most Wisconsin cranberry growers.
  • Spraying when bees are least active. Most bees forage from early morning until shortly before sunset. Therefore, the best time to apply a pesticide, especially during bloom (if allowed by the pesticide label), is in the late evening or at night.
  • Limiting pesticide drift. Whether plants are blooming or not, using a boom sprayer allows for direct application of pesticides onto cranberry plants.  Other methods that can reduce pesticide drift include calibrating your boom to optimize spray pressure and volume, selecting drift-reducing nozzles, avoiding pesticides with small particles that easily drift, and spraying when winds are under 10 mph and when relative humidity is above 50%.
  • Using insecticides and fungicides that have a reduced risk for bees. See the table below for insecticides and fungicides that are least toxic for bees.
(IRAC or FRAC code)
Active Ingredient(s)
Trade Names

(IRAC code)*

diamide (28) chlorantraniliprole Altacor
diacylhydrazine (18) methoxyfenozide




biological Bacillus thuringiensis Biobit, Dipel

(FRAC code)*

strobilurin (11) azoxystrobin Abound, Evito
chitin synthase inhibitor (19) polyoxin D zinc salt Oso
biological Reynoutria sachalinensis Regalia

*  Note that rotating Insecticide Resistance Action Committee (IRAC) classes and Fungicide Resistance Action Committee (FRAC) codes (modes of action) will help delay development of pesticide resistance.

Strengthen your working relationship with beekeepers.  Optimal cranberry pollination requires cooperation between grower and beekeeper.  In some cases, outlining expectations in a signed, written contract can be the best way to prevent misunderstandings.  Topics to consider and discuss with your beekeeper can include, but are not limited to:

  • Hive inspections. Inspecting a random sample of 10% of hives when they are brought onto a march can help ensure that hives are of high quality and contain healthy bees.  Ideally, a third party should conduct the inspections in the presence of both beekeeper and grower.
  • When bees are introduced onto a cranberry marsh and the duration of their stay are important factors in optimizing cranberry pollination, as well as for maintaining honeybee health.  Bees should be brought onto a marsh at around 15% bloom.
  • Hive placement. Within the limits of your bed layout and equipment needs, it is best to place hives in the center of a marsh or near marsh edges with wild habitat, but away from water reservoirs, as bees from hive near water seem to be less likely to visit cranberry plants.
  • Exposures to sprays. Be explicit about when, how and what may be sprayed during bloom.

For more information on improving cranberry pollination:  Watch for UW Extension bulletin A4155, “Practices to improve pollination and protect pollinators in Wisconsin cranberry” (available soon at, or University of Wisconsin Garden Facts XHT1213 “Pollinators” (available at, or contact your county Extension agent.

How to Properly Prune Deciduous Trees

Why should I prune my trees? Pruning is important for a variety of reasons. Pruning can help control the size of a tree, direct growth, influence flowering or fruiting, or maintain plant health and appearance. Pruning can also increase the safety of a tree by removing broken, diseased, dead, or dying branches. In addition to pruning, selecting plants that are suited to your environment and location are very important. The ultimate height and spread, in addition to location of overhead power lines, should be taken into account when selecting trees for landscaping.

The three step method of pruning large limbs.
The three step method of pruning large limbs.

What should I prune?

  • Newly planted trees: Newly planted trees should not be pruned unless a branch is broken, diseased or dead. These trees need foliage to produce carbohydrates (sugars) that are then transported to the root system for initiation of new roots.
  • Young trees: After a young tree is established for two to five years, the tree can be pruned to encourage a well-branched canopy. Lower branches can be removed to raise the canopy, if desired. Scaffold branches to be maintained in the tree should be selected such that they are 12-18 inches apart, are evenly distributed around the trunk and have wide crotch angles. Remove no more than 13 of the total crown of a tree at one time. Young trees also need corrective pruning to remove crossing branches, double leaders, watersprouts, and root suckers.
  • Older trees: Older, established trees, if properly trained when young, require little pruning. These trees should never be topped as this leads to poor branch structure and increased limb breakage. Use the three-point method of limb removal for pruning large branches (see diagram above and description below). This method ensures proper pruning and closure of wounds. Contact a certified arborist to prune larger limbs and remove trees, particularly if the tree is close to power lines or buildings.

The 3-point method of proper pruning of large limbs

When doing any type of pruning, always use a sharp pruning saw for making pruning cuts. Also, be sure to disinfect your pruning tools with alcohol or a 10% bleach solution after each pruning cut to avoid spreading diseases.

  • Step one: Select the branch that you want to remove. On large limbs, the first cut should be 12 to 18 inches from the limb’s point of attachment. The pruning cut should be an undercut made 12 way through the branch (see diagram). This pruning cut is very important because it relieves weight from the branch collar and prevents accidental tearing of bark from the tree’s trunk when the limb is removed.
  • Step two: The second pruning cut should be made on the outside of the first cut (i.e., farther from the trunk). Cut all the way through the limb from the top down, thus removing the weight of the branch.
  • Step three: The final cut should be made next to the tree’s trunk outside of the branch collar. Cut from the top down and cut all the way through the remaining branch stub. The branch collar should be left intact. DO NOT cut the branch flush with the tree’s trunk. A proper cut avoids large wounds, and allows the tree’s wound to close quickly.

Should I use wound treatments? In general, wound treatments, such as tree paint or wound dressing, are not recommended. These compounds slow down wound closure and promote decay. One exception when wound treatments are recommended, is the case of oak trees that are pruned during the growing season. Using wound treatments on oaks is important to keep out insects that transmit the oak wilt fungus (see University of Wisconsin Garden Facts X1075).

When should I prune trees? Most deciduous trees should be pruned in late fall to winter. At this time of year, you can see the overall branch structure easily, and most insects and disease causing organisms are not active. Late fall/winter pruning is especially important for oak trees to help prevent spread of the fungus that causes oak wilt (see University of Wisconsin Garden Facts X1075). Late spring and summer are usually not good times of year to prune because disease pathogens are present and wound closure is slower. If you prune in late winter, some trees may bleed or ooze sap excessively in the early spring. The bleeding may be unsightly, but does not harm the tree. Examples of trees that bleed excessively are maple, willow, birch, walnut, beech, hornbeam, elm, and yellowwood.


  • Branch collar: the ring of trunk tissue that surrounds a lateral branch at the point of attachment to the stem.
  • Double leaders: two major, terminal growing points located at the top of the tree.
  • Root suckers: vigorous, upright, adventitious shoots that arise from latent buds below the graft union or at the base of the tree.
  • Scaffold branches: the large branches that form the main structure of the crown of a tree.
  • Topping: an improper pruning technique that reduces the height of a tree by removal of large branches back to larger primary branches. This technique is not recommended.
  • Watersprouts: vigorous, vertical, adventitious shoots that arise from latent buds above the ground or graft union on older wood.

For more information on pruning: See UW-Extension bulletins A1817, A1771, A1730 and University of Wisconsin Garden Facts XHT1013, XHT1015, or contact your county Extension agent.


What are zinnias? Zinnias are one of America’s most popular annual bedding plants, but have humble origins as descendants of nondescript wildflowers native to the southwest U.S., Mexico and Central America. The zinnia was named after the 18th century German botanist Dr. Johann Gottfried Zinn, who wrote the first description of small, weedy plants that he discovered in the Mexican deserts. These plants had dull purplish-red, daisy-like flowers with single petals surroundng a protruding cone. Early varieties of garden zinnias were introduced in the U.S. in 1796, with double forms appearing in the mid-1800’s. Interest in zinnias increased in 1920 when Bodger Seeds Ltd. introduced the dahlia-flowered varieties ‘Giant Dahlia’ and ‘California Giant’. These varieties had large, flat-flowered heads and multiple colors. ‘California Giant’ eventually won a gold medal from the Royal Horticulture Society of England.

Zinnias can be a bright-colored addition to any garden, particularly when planted in mass.
Zinnias can be a bright-colored addition to any garden, particularly when planted in mass.

Today, zinnias come in a wide variety of flower forms: single, semidouble, or double. Single-flowered zinnias have one row of petals and the center of the flower is exposed. Semidouble-flowered zinnias have many rows of petals and the center can still be seen. Dahlia-type zinnias (typically semidouble) have large, flat blossoms. Double-flowered zinnias have so many rows of petals that flower centers are hidden. There are several types. Beehive-types have small blooms with stacks of flat petals resembling small beehives. Button-types are similar but have flatter flowers. Cactus-types have twisted, bent petals with rolled edges.

Although there are more than a dozen species of zinnias, only a few species are regularly planted in gardens. Zinnia elegans is the most common. It grows up to three feet tall and has single or double flowers in pink, rose, red, cherry, lavender, purple, orange, salmon, gold, yellow, white, cream or light green. Flowers range in size from one to seven inches in diameter and can be solid-colored, multicolored or zoned. Flower shapes include round, domed or ball-shaped, as well as dahlia-like or chrysanthemum-like. Tetraploid varieties (having four sets of chromosomes, rather than the normal two) were developed in the 1950’s, and these varieties produce larger flowers on stronger stems, grow more vigorously and have increased disease resistance. Hybrid varieties were developed soon thereafter. There are many varieties of Z. elegans available at garden stores, including the following.

  • The Border Beauty series has plants that grow up to 20 inches tall and have 3½-inch-wide semidouble to double, dahlia-like flowers.
  • The Peter Pan series has dwarf hybrids that grow up to 12 inches tall and have very large (up to five-inch-wide), slightly curled, double flowers. Seven separate colors in this series have been recognized as All-American Selections (AAS) winners.
  • The Ruffles series was developed for cut flower production. Plants grow up to 30 inches tall and have 2½-inch-wide, ball-shaped flowers with ruffled petals on stiff, upright stems. ‘Scarlet Ruffles’ was named an AAS winner in 1974, ‘Cherry Ruffles’ and ‘Yellow Ruffles’ AAS winners in 1978.

Z. angustifolia (synonym Z. linearis) has small, single, golden-orange flowers with yellow stripes, and narrower foliage than Z. elegans. These compact plants grow eight to 12 inches high, and can spread to two feet. The variety ‘Crystal White’ has pure white flowers with yellow centers and was an AAS winner in 1997. A cross of Z. elegans and Z. angustifolia yielded the Profusion series of zinnias which has compact plants with two to three-inch-wide, single flowers. Members of this series have superior heat and humidity tolerance, and tend to be disease resistant. Two members of this series ‘Cherry Profusion’ and ‘Orange Profusion’ won gold medals from AAS in 1999 (the first awarded to flowers in 10 years).

Z. haageana (Mexican zinnia) grows up to 18 inches tall and has small 1½ to two-inch-wide flowers on long stems. Flowers may be single or double, solid or bicolor, in red, mahogany, yellow and orange. Two popular varieties may be available at your local garden center.

  • ‘Persian Carpet’ (an AAS winner in 1952) grows up to 15 inches tall and has two-inch-wide, double, bicolored flowers of gold, maroon, purple, chocolate, pink or cream;
  • ‘Old Mexico’ (an AAS winner in 1962) has bushy, compact, 18-inch-tall plants with double, 2½-inch-wide blooms of deep, rich mahogany highlighted with yellow-gold.

Z. pauciflora (synonym Z. peruviana) grows up to 30 inches tall and produces 1½-inch-wide, single, red or yellow flowers with button-like centers. This zinna is good for cutting and drying, and has powdery mildew resistance. Only varieties ‘Bonita Red’ and ‘Bonita Yellow’ are readily available.

Zinneas can be effectively used in gardens as an edging plant.
Zinneas can be effectively used in gardens as an edging plant.

Where do I get zinnias? Zinnias can be purchased as bedding plants, but local garden centers often have only a limited selection of varieties. As an alternative, zinnias can be started from seed, either indoors four to six weeks before the last expected spring frost, or directly in the garden when the soil warms sufficiently. Germination takes five to seven days. Many references warn that zinnias do not like being disturbed and should not be moved after seeding. However, plants can be seeded individually in cells of seed-starting trays or even transplanted into these cells from mass plantings. When transplanting into trays, wait until the first true leaves have emerged. Separate roots as carefully as possible and place seedlings into their new cells up to the first set of leaves (the seedling leaves). Select appropriately sized tray cells based on the predicted size of the varieties being grown. Otherwise, tall varieties may outgrow their cells before it is time to plant them outdoors. Once the danger of frost has passed, zinnias can be transplanted outside. However, do not expect substantial growth until temperatures are above 50°F.

How do I grow zinnias? Zinnias do best in full sun in fertile, well-drained soil. Space plants four to 24 inches apart depending on variety. When growing zinnias for cut flowers, crowd plants to encourage longer stems. To produce bushier plants, pinch the tops out of plants when they are four to six inches high. Remove faded blossoms to encourage new blooms. Plants should be kept well-watered and fertilized two times per month for optimum bloom. Most varieties begin to bloom when very young and continue to bloom until frost.

Zinnias have few insect pests, but occasionally can have problems with aphids (see University of Wisconsin Garden Facts XHT1043), four-lined plant bugs (see University of Wisconsin Garden Facts XHT1101) and spider mites. Common diseases of zinnias include powdery mildew (see University of Wisconsin Garden Facts XHT1005), Alternaria leaf spot and bacterial leaf spot.

How do I use zinnias most effectively in my garden? Zinnias make good edging plants, but are also effective when grown in masses. Taller varieties make good background plants in flowerbeds, while smaller varieties are suitable for container plantings. Zinnias are great additions to butterfly gardens and many varieties make excellent cut flowers.

For more information on zinnias: Contact your county Extension agent.

Zebra Iris

What is zebra iris? Zebra iris (Iris pallida), also known as sweet iris, Dalmatian iris or variegated iris, is a very old garden plant. It is native to rocky areas of northern Italy and the eastern Mediterranean including Dalmatia, a province of Croatia (hence one of the plant’s common names). Zebra iris was one of the primary species used in the development of the tall bearded iris. Dried zebra iris root (along with the roots of other species of iris) is a source of orris root powder. This powder was used medicinally (and for its supposed magical and alchemical properties) in medieval times, as well as a perfume and potpourri fixative for many centuries. Roots may require several years of drying before fully developing their fragrance. Orris oil (derived from fresh roots) is used as a flavoring in soft drinks, candies and chewing gum.

Zebra iris produces clumps of sword-like leaves.  Several varieties have striped foliage.
Zebra iris produces clumps of sword-like leaves. Several varieties have striped foliage.

Zebra iris produces low clumps of sword-like leaves that remain nearly evergreen in areas with mild winters, but die back to the ground in colder climates. The original color of the foliage of this species was a solid bluish-green. Newer cultivars of zebra iris have leaves with vertical stripes of blue-green and either silvery-white (varieties ‘Alba-variegata’ and ‘Argentea Variegata’) or creamy yellow to pale gold (varieties ‘Aurea-variegata’ and ‘Variegata’).

Zebra iris cultivars are grown primarily for their attractive striped leaves, although in early summer they do produce pretty, lavender-blue flowers with small, yellow beards on three-foot-tall scapes. The tall branched flower stems may need staking in windy, exposed areas. The highly fragrant flowers have a distinctive scent that has been variously described as reminiscent of grape jelly, orange blossom, or vanilla. Zebra iris is hardy in zones 4 through 9.

Where do I get zebra iris? Zebra iris plants can be purchased at local nurseries and garden centers. Once established, clumps should be divided as needed every three to four years after flowering has occurred, just as you would a bearded iris.

How do I grow zebra iris? Grow zebra iris in full sun and well-drained soil for best results. However, zebra iris will tolerate more shade than many bearded irises do, and will also thrive in heavy clay and medium clay loam soils. When planting zebra iris, place rhizomes partly above the soil and keep newly transplanted plants well-watered. Once established, zebra iris is somewhat drought tolerant and require little maintenance. Simply remove old foliage before new leaves emerge in early spring. Note that varieties with gold leaf coloring appear to be more vigorous than those with white leaf coloring.

Zebra iris has few pests. Rabbits and deer rarely bother this plant and iris borer (see University of Garden Facts XHT1041) is much less of a problem than on bearded iris.

Zebra iris produces lavender-blue flowers with small yellow beards.
Zebra iris produces lavender-blue flowers with small yellow beards.

How do I use zebra iris most effectively in my garden? The striking foliage of zebra iris makes a great accent in a sunny perennial border, especially near the front. The stiff upright form of zebra iris offers good contrast to mounded shapes, while the dramatic coloring of striped varieties stands out among solid-colored foliage, particularly purple-leaved plants. Interplant with low, open perennials or taller ramblers such as pincushion flower (Knautia macedonica). Zebra iris also pairs nicely with traditional perennials such as fern leaf yarrow (Achillea ‘Moonshine’), purple coneflower (Echinacea spp.) and ‘Husker Red’ beard-tongue (Penstemon ‘Husker Red’), and is a good companion with Arkansas bluestar (Amsonia hubrechtii). Or use zebra iris as a neat edging in larger plantings. Zebra iris is a natural around water and really stands out in rock gardens. It can also be stunning in suitable containers.

For more information on zebra iris: Contact your county Extension agent.

Yellow Corydalis

What is yellow corydalis? Yellow corydalis (Corydalis lutea = Pseudofumaria lutea) is a shortlived perennial in the bleedingheart family (Fumariaceae). The genus Corydalis has approximately 300 species, and the name derives from the Greek ‘korydalis’ meaning crested lark, a reference to the fact that the plants’ flowers resemble a lark’s head. Other common names of yellow corydalis include yellow fumitory, hollowort, and yellow larkspur. Native to the southern Alps of Europe, this plant is hardy in zones 4 through 8.

Yellow corydalis plants have finely cut foliage with yellow, tubular flowers.
Yellow corydalis plants have finely cut foliage with yellow, tubular flowers.

Yellow corydalis plants form neat mounds of finely cut, delicate-looking light-green to blue-green foliage, somewhat resembling the foliage of maiden hair ferns or bleeding hearts. The pinnately compound leaves have three lobes, and are pale green above and glaucous (i.e., waxy) below. The leaves are borne on weak, hollow and fleshy stems. Plants grow up to 18 inches tall, but often are much shorter.

In mild climates, yellow corydalis remains evergreen (although not necessarily attractive), but in climates with colder winters, dies back to the ground. In very hot summers or during drought, plants may also die back, but they often resume growth in the fall when cooler, moister conditions prevail. In Wisconsin’s relatively cool climate, when planted in a moist site, yellow corydalis does not die back at all. This is in contrast with the majority of other Corydalis species that are more easily heat-stressed and prone to dieback.

As its name suggests, yellow corydalis produces bright, golden-yellow flowers. It blooms over a long period, from late spring through frost. The one to two inch long flowers have four petals arranged in an irregular tubular shape with a spur in the back. Flowers are borne in racemes of six to 16 flowers on stems that rise above the foliage. Slender, dehiscent capsules (i.e., seed pods that naturally break open along a seam) follow the flowers. Capsules eventually burst to scatter their seed.

In addition to C. lutea, there are other Corydalis species with yellow flowers that are suitable for use in the garden.

  • C. aurea (hardy to zones 3 through 8) is known as scrambled eggs and is a biennial that produces small flowers in the spring of the second year of growth.
  • C. cheilanthifolia (hardy to zones 4 through 9) has fern-like leaves and upright, butter-yellow flower clusters. The leaves become bronze in the fall.
  • C. ochroleuca (hardy to zones 5 through 8) has blue-green leaves, with creamy yellow-white flowers with green lips and yellow throats.

While useful as an ornamental, yellow corydalis does have one potentially problematic characteristic. It is toxic to horses, causing mouth sores, gingivitis, colic and sudden death (if enough is ingested). Therefore, yellow corydalis should not be allowed to invade pastures.

Yellow corydalis makes an excellent border plant.
Yellow corydalis makes an excellent border plant.

Where do I get yellow corydalis? Yellow corydalis plants are available at many nurseries and garden centers that stock perennials. Once established in the garden, this plant tends to self-seed prolifically, and can become somewhat weedy in certain conditions, although it is easily removed where not wanted. Yellow corydalis commonly establishes around stone walls or in gravelly soil. Seedlings can be transplanted in early spring. However, established plants often do not perform well if moved. If you do transplant yellow corydalis, plants will require extra watering and will often struggle for the remainder of the season. Yellow corydalis plants are also not easily divided, but divisions can be made in early spring. Although it self-seeds readily, yellow corydalis is not easy to germinate indoors due to its complex dormancy requirements. To germinate the seeds, sow them in a moist potting medium, then place them in a plastic bag and keep at room temperature (approximately 70ºF) for six weeks. Move the seeds to near freezing conditions (28 to 38ºF) for six to eight weeks, then return to cool conditions (50 to 60ºF). If there is no germination after several weeks, repeat the heating and cooling steps a second time.

How do I grow yellow corydalis? Yellow corydalis grows well in either sun or light shade. It prefers well-drained soil and does best with good moisture during hot weather. However, it does not tolerate wet soils during winter. Yellow corydalis likes ordinary to rich, humusy soil, but tolerates drier, gravelly soil and sandy loam to clay as well. In heavier, wetter soils, shallow planting may help yellow corydalis survive Wisconsin’s harsh winters. Yellow corydalis is relatively insect pest and disease-free.

How do I use yellow corydalis most effectively in my garden? Yellow corydalis can be extremely attractive when used to edge borders or walkways. In rock gardens, cottage and woodland gardens, it is a good filler and may naturalize. It will grow well in stone walls in cool conditions. Yellow corydalis combines well with bleeding heart (Dicentra spectabilis), lady’s mantle (Alchemilla mollis), lungwort (Pulmonaria spp. – See University of Wisconsin Garden Facts XHT1174), foam flower (Tiarella spp.), hosta (Hosta spp.), leopard plant (Ligularia spp.), and many other perennials in a shade garden. Try yellow corydalis in sunny areas under taller plants like peonies (Paeonia spp.) or daylilies (Hemerocallis spp.).

For more information on yellow corydalis: Contact your county Extension agent.

Wood Mulch and Tree Health

What are the benefits of wood mulch? Wood mulch is typically available as chipped wood, or shredded or chunked bark, and can contribute to tree health in many ways. When high quality, composted mulches are applied two to four inches deep in a ring three to six feet in diameter (or greater) from the trunk of a tree, mulch can help preserve moisture, control weeds, limit damage to the trunk from mowers and string trimmers and moderate the soil temperature. Use four inches of mulch when soils are light and well-drained, and two inches of mulch on heavier, clay soils.

Use of properly composted mulches can be beneficial to trees and shrubs in the landscape.
Use of properly composted mulches can be beneficial to trees and shrubs in the landscape.

Can wood mulch harm trees? Use of improperly composted mulches (some-times called “sour mulches”), can lead to tree nutrient deficiencies. Sour mulches can also produce gases like methane and ammonia that can be toxic to plants. Foliage on trees surrounded by sour mulches may initially turn yellow, then brown, die and fall off. If your mulch smells like vinegar, ammonia or sulfur, it is likely a sour mulch, and should be removed. Replace the sour mulch with a high quality, composted mulch and consult with your local UW-Extension agriculture/horticulture about testing the soil for nutrient deficiencies. Fertilize appropriately based on the results of these tests.

Improper application of mulch can also lead to problems. Piling wood mulch up against the trunk of a tree can keep the bark underneath excessively wet. This wetness can contribute to bark decay. In addition, use of thick mulch layers (greater than four inches) can lead to overly wet soils that are favorable for development of root rots (see University of Wisconsin Garden Facts X1070). To avoid these problems, make sure mulch is applied at least one to two inches away from the trunk of the tree and that the mulch layer is the appropriate thickness for the soil type in your landscape (see above).

Does woody mulch harbor or attract insects? Insects such as earwigs (see UW-Extension bulletin A3640), centipedes (see University of Wisconsin Garden Facts X1113), millipedes (see University of Wisconsin Garden Facts X1108) and sowbugs (see University of Wisconsin Garden Facts X1110) can feed on decaying organic matter in mulches. While these insects are often only nuisances, earwigs can feed on and cause damage to a variety of ornamentals, particularly to flowering plants. If mulch is used near entrances to a home or around basement windows, these unwanted insects may get inside.

Termites ingest wood and can be attracted to wood mulch, but new termite colonies are not likely to become established due to use of wood mulches. Typically termites are not a problem in Wisconsin, and when colonies are found, they occur only in the southern half of the state.

Carpenter ants (see UW-Extension bulletin A3641) and powderpost beetles (see University of Wisconsin Garden Facts X1053) are unlikely to utilize mulch as a food source because conditions required for their development would not be satisfied by wood mulch. Carpenter ants do not ingest wood as a food source; instead, they chew non-living wood (in trees or landscape timbers, etc.) to excavate galleries in which they live and raise their young. Since wood mulch is composed of small wooden pieces, it would not serve as a home. To avoid potential insect problems, keep mulch as far away from the foundation of your home as possible and seal all holes and crevices where insects might use as entry points. Also, periodically inspect landscape timbers and the house for termites.

Does woody mulch harbor tree pathogens? Wood mulch may come from many sources, including trees and shrubs that have died from a wide range of diseases. To be harmful to your trees, disease-causing organisms (pathogens) would have to survive in mulch and these organisms would have to move from the mulch either directly, or through the soil, to their new host – your tree. There is currently very little research on this topic.

Elm trees killed by Dutch elm disease (see University of Wisconsin Garden Facts X1076), can serve as breeding areas for native and European elm bark beetles. Bark beetles that breed in logs or firewood from these trees can pick up the fungi that cause Dutch elm disease (Ophiostoma ulmi and Ophiostoma novo-ulmi) and carry these fungi from tree to tree. Chipping infected elm trees creates an unfavorable environment for bark beetles yet there is no scientific literature that describes the level of risk of transmitting the Dutch elm disease fungi from wood chips or bark chunks to healthy elms.

Oak trees killed by oak wilt (see University of Wisconsin Garden Facts X1075) can be attractive to several sap-feeding beetles that can potentially pick up the oak wilt fungus (Ceratocystis fagacearum) and move it in the landscape. This process is affected by moisture and temperature and would likely be disrupted by the chipping and composting process yet there is no scientific literature that describes the level of risk of transmitting the oak wilt disease fungus from wood chips or bark chunks to healthy oaks.

Recent research at the University of Wisconsin-Madison suggests that wood chip mulches produced from trees suffering from Verticillium wilt (see University of Wisconsin Garden Facts X1008) can serve as a source of the fungus (Verticillium dahliae) that causes the disease. These studies show that Verticillium can survive for at least one year in mulch and that use of this contaminated mulch can lead to Verticillium wilt in both woody and herbaceous plants. Therefore use of mulches produced from trees with Verticillium wilt should be avoided.

For more information on proper tree care: See UW-Extension Bulletin A1817, or contact your county Extension agent.