Category Archives: General Horticulture/Weeds

Wisconsin Lawn Care Calendar

Regular care and maintenance will yield a lawn that is lush and beautiful.
Regular care and maintenance will yield a lawn that is lush and beautiful.

The following lawn care calendar provides an overview of home lawn maintenance. Not all lawns require every maintenance activity. Be sure to customize the care of your lawn to its specific problems and needs. For details on specific activities listed below, check out the University of Wisconsin-Extension bulletins (available at and University of Wisconsin Garden Facts (available at that are referenced at the end of this fact sheet. Finally, be sure to read and follow all label instructions of any pesticides that you select to ensure that you use these products in the safest and most effective manner possible.


  • Rake and clean up winter debris as weather allows.
  • Reseed bare spots, and establish a new lawn, if you desire.
  • Apply a pre-emergent crabgrass herbicide to your established lawn.
  • Mow your lawn to remove 1/3 of the current grass height. Grass should be 21/2 to 31/2 inches tall after mowing.


  • After your grass is actively growing, core aerate your lawn if the thatch layer is over one inch thick.
  • Late in May (e.g., around Memorial Day), fertilize your lawn using a controlled-release or slow-release formulation. For grass growing in the sun, use the label rate of the fertilizer that you have selected. For grass growing in the shade, apply half of the label rate.
  • Apply an herbicide to your established lawn to control actively growing broadleaf weeds. DO NOT use herbicides on newly seeded areas. If possible, apply the herbicide to weeds when they are blooming. Many fertilizer products also contain herbicides for broadleaf weed control, so combining fertilizer and herbicide applications may be possible.


  • If you have not applied one previously, apply an herbicide to your lawn for broadleaf weed control.
  • Begin watering your lawn as needed for the summer. Or alternatively, do not water and allow the lawn to go dormant (i.e., turn brown) if natural rains are insufficient.
  • Watch for insect pests, diseases, and other lawn problems.


  • Water your lawn as needed. If you do not water, your lawn will naturally go dormant.
  • Early in July (e.g., around Independence Day), fertilize with a controlled-release or slow-release fertilizer. For grass growing in the sun, use the label rate of the fertilizer that you have selected. For grass growing in the shade, apply half of the label rate. If your lawn has been consistently fertilized for 10 to 15 years, if you leave clippings on your lawn when you mow, or if your lawn has gone dormant, skip this application.
  • Apply a grub control product to your lawn if there is a history of grub problems and/or your lawn is a high maintenance (i.e., regularly watered) lawn.
  • Avoid seeding and spraying for weeds.
  • Watch for insect pests, diseases, and other lawn problems.


  • Water your lawn as needed.
  • Establish a new lawn or renovate your current lawn. Note that mid-August to mid-September is the best time to establish a lawn in Wisconsin.
  • Watch for insects, diseases, and other lawn problems.


  • Early in September (e.g., around Labor Day), fertilize your lawn using a controlled-release or slow-release formulation. For grass growing in the sun, use the label rate of the fertilizer that you have selected. For grass growing in the shade, apply half of the label rate.
  • Apply an herbicide to your established lawn to control broadleaf weeds. Fall is the best time to apply herbicides for weed control. DO NOT apply herbicides to lawns planted in August or September.
  • Core aerate actively growing lawns if the thatch layer is over one inch thick, or if the soil is compacted.


  • Apply a broadleaf herbicide to your lawn if you did not apply one in September and the weeds are still growing.
  • If you have removed clippings from your lawn all season, fertilize your lawn in early October using a controlled-release or slow-release formulation. For grass growing in the sun, use the label rate of the fertilizer that you have selected. For grass growing in the shade, apply half of the label rate.


  • Continue to mow your lawn until it goes dormant for the winter.

For more information on lawn care and lawn pests: See University of Wisconsin-Extension bulletins A1990, A2303, A3179, A3237, A3271, A3275, A3434, A3435, A3700, A3710, and A3714 (available at, and University of Wisconsin Garden Facts XHT1018, XHT1023, XHT1062 and XHT1114 (available at, or contact your county Extension agent.

Wild Parsnip

What is wild parsnip? Wild parsnip (Pastinaca sativa) is an aggressive Eurasian member of the carrot family that grows in sunny areas and tolerates dry to wet soil types. It is often found along highways, in prairies or bordering farmed fields. The plant spreads primarily by seed. Sap from the plant can cause phytophotodermatitis, a light sensitive reaction on your skin. If the juice from broken stalks, leaves or flowers contacts your skin and then is exposed to sunlight, a skin rash will result 24-48 hours later. Symptoms range from slightly reddened skin to large blisters. The blisters may produce a sensation similar to a mild to severe sunburn. The blisters do not spread or itch, as poison ivy rashes do, but they are uncomfortable and leave brown scars that last for a number of months to two years. See your doctor if you develop burn symptoms.

A wild parsnip plant.
A wild parsnip plant.

What does wild parsnip look like? At maturity, wild parsnip is about four to five feet tall. It bears many large flat clusters of yellow-green flowers on a thick stem. Flowers appear from the first of June through July in southern Wisconsin. Seeds form around the end of July. The plant will often have both flowers and seed capsules at the same time. Seeds are flat, oval and about the size of a sunflower seed. After flowering and producing seed, the plant turns brown and dies. The plants have a rosette of basal leaves, as well as leaves arranged alternately on the stem. The leaves are branched into leaflets and have heavily toothed margins. The plant can be confused with prairie parsley (Polytaenia nuttallii), an endangered native species in Wisconsin. Prairie parsley has sparse, light yellow flowers, and long leaves branched into leaflets with few teeth.

How can I control wild parsnip? Prevention is the best way to control wild parsnip. When wild parsnip is first detected in an area, it can be cut below ground level with a sharp shovel. Be sure to wear long sleeves, long pants and gloves when working with plants. Also, try to work after sunset so that exposure to sunlight does not occur. Plants can also be pulled by hand, if you wear protective gloves. If the wild parsnip population is fairly large, you may use a brush-cutter just after peak bloom and before the plant sets seed. Remove all the cut material. A few weeks later, repeat the treatment to prevent plants from re-sprouting. Treatments may need to be repeated over several years. Herbicides containing the active ingredient glyphosate are also effective against wild parsnip. In high quality natural areas such as prairies, the Department of Natural Resources recommends burning the site and then applying spot treatments of a 1-3% glyphosate solution to wild parsnip rosettes if they re-sprout after burning.

For more information on wild parsnip: See the DNR publication ER-090-97 – “Wisconsin Manual of Control recommendations for Ecologically Invasive Plants”, or contact your county Extension agent.


Using Crop Rotation in the Home Vegetable Garden

What is crop rotation? Crop rotation is one of agriculture’s oldest cultural practices. In a home vegetable garden, crop rotation involves changing the planting location of vegetables within the garden each season. Crop rotation is used to reduce damage from insect pests, to limit the development of vegetable diseases, and to manage soil fertility.

Use of crop rotation can lead to a healthier, more productive garden.
Use of crop rotation can lead to a healthier, more productive garden.

Why is crop rotation important? Each vegetable can be classified into a particular plant family. Plants belonging to the same family oftentimes are susceptible to similar insect pests and diseases, and have similar nutrient requirements. When vegetables classi­fied in the same plant family are grown year after year in the same area of a garden, they provide insect pests with a reliable food source and disease-causing organisms (i.e., pathogens) with a continual source of host plants that they can infect. Over time, insect pest and pathogen numbers build in the area and damage to vegetable crops increases. Using crop rotation helps keep insect pest and pathogen numbers at low levels. In addition, the type of vegetable grown in a particular area in a garden has a direct effect on the fertility of the soil in that area. Each vegetable is unique in the type and amount of nutrients it extracts from the soil. Crop rotation can even out the loss of different soil nutrients and allow time for nutrients to replenish.

How do I plan a crop rotation for my home garden? Plan the crop rotation for your vegetable garden based on the types of vegetables that you grow. Vegetable crops in the same plant family should NOT be planted in the same area of a garden year after year. For example, if tomatoes are planted in a bed or area of a garden one year, vegetable crops such as peppers, eggplant, potatoes and tomatoes should not be planted in the same bed or area the following year because all of these plants belong to the nightshade family (Solanacaeae). Table 1 provides a guide to common garden vegetables and their plant families.

Crop rotations vary in complexity. They can be as simple as changing vegetable locations annually, or can be extremely involved, using cover crops/green manures, and/or leaving parts of a garden fallow (i.e., planting nothing in an area) each year. Cover crops/green manures are planted before, after or in place of a vegetable crop to improve soil fertility and drainage, prevent erosion, and hold nutrients. See University of Wisconsin Garden Facts XHT1209, “Using Cover Crops and Green Manures in the Home Vegetable Garden” for details. Leaving an area fallow is often less desirable than planting a cover crop/green manure because an area without a planted crop tends to be more prone to erosion and can end up with a soil that does not drain properly. Alternatively, the area may become filled with weeds that will cause problems for future vegetable production.

For crop rotation to be most effective, DO NOT plant an area with vegetables or cover crops/green manures from the same plant family more than once every three to four years. This length of crop rotation can be difficult to achieve in small gardens, but even changing plant families grown in an area of a garden from year to year is helpful in managing insect pests and diseases. To help in planning crop rotations, keep a garden log or map as a reminder of where vegetables are planted each year.

Table 1. Common vegetables and their plant family classifications.

Carrot Family
Carrot, celery, parsley, parsnip
Goosefoot Family
Beet, spinach, Swiss chard
Gourd Family
Cucumber, muskmelon, pumpkin, summer squash,
watermelon, winter squash,
Grass Family
Ornamental corn, popcorn, sweet corn
Mallow Family


Mustard Family
Broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collard, kale, kohlrabi, mustard greens, radish, rutabaga, turnip
Nightshade Family
Eggplant, pepper, potato, tomato
Onion Family
Chives, garlic, leek, onion
Pea Family
Bush bean, kidney bean, lima bean, pea, pole bean, soybean
Sunflower Family
Endive, lettuce, sunflower

For more information on using crop rotation in the home vegetable garden: Contact your county Extension agent.

Thanks to Diana Alfuth, Steve Huntzicker, Mark Kopecky and Erin Silva for reviewing this document.

Using Cover Crops and Green Manures in the Home Vegetable Garden

What are cover crops and green manures? Cover crops are plants grown in a garden to improve a soil’s physical structure and fertility. As cover crops grow, they become reservoirs for important plant nutrients such as nitrogen, phosphorus and potassium, as well as micronutrients. Cover crops also help prevent soil erosion, reduce weed problems, and provide a habitat for beneficial insects. Working cover crops into a garden returns nutrients to the soil making these nutrients available to future vegetable crops. Working cover crops into a garden also increases soil organic matter, improving the soil’s overall physical structure. Improved soil structure leads to better water infiltration, as well as better nutrient and water-holding capacity.

Green manures [oftentimes plants in the pea (legume), mustard and grass families] are a subset of cover crops that are grown specifically to increase soil organic matter and nutrients. Pea family green manures are unique in that they increase soil nitrogen levels due to bacteria (Rhizobium spp.) in their roots that convert (i.e., fix) nitrogen gas from the air into a form of nitrogen that can be used by plants. Note that you should treat seeds of pea family green manures with the appropriate bacterium (available from garden supply centers) the first time you grow the crop because the bacterium may not be present naturally in your soil. Cover crops and green manures can be incorporated into a garden as part of an annual vegetable rotation (see University of Wisconsin Garden Facts XHT1210, “Using Crop Rotation in the Home Vegetable Garden”), or planted simply to improve the soil quality in a fallow garden area.

Ryegrass is a common cool season cover crop.
Ryegrass is a common cool season cover crop.

How do I choose a cover crop or green manure? There are a large variety of cover crops, and choosing one for your vegetable garden depends on several factors. See Table 1 for examples of cover crops that can be useful in home gardens. Cover crops and green manures can be planted before vegetables are planted, after harvest, in place of a vegetable crop, or in a fallow area of a garden.

Warm season cover crops (e.g., buckwheat) are planted in spring or summer, before or in place of a vegetable crop. They grow quickly in a garden, preventing weeds from establishing and protecting bare soil from water erosion and crusting.

Cool season cover crops are planted in late summer to early fall, after vegetables are harvested. These cover crops are planted early enough to establish some growth before the winter, and can help prevent soil erosion and crusting during fall rains. Depending on the crop, plants may be killed by freezing winter temperatures, or become dormant during the winter and resume growth in the spring. Fall-planted cover crops that are winter-killed (e.g., oats) are a good choice for gardeners needing to immediately work the soil in the spring to plant early crops such as spring greens, peas, and radishes. Fall-planted crops that resume growth in the spring (e.g., winter rye) need to be killed by tillage prior to planting vegetables, and are a good choice for areas that may be planted to summer crops such as tomatoes, peppers, and squash.

When choosing a cover crop, select one that you can easily cut and work into the soil.

How do I use and manage a cover crop or green manure? To plant a cover crop or green manure, first clear the planting area of any large stones and other debris. Rake the area smooth and broadcast seed according to the seeding rate given in Table 1 or as recommended by the seed provider. Rake the area again to incorporate the seeds into the soil, and lightly water the area.

To prevent the cover crop from self-seeding in other areas of your garden, and to utilize the cover crop to its fullest potential, cut down plants when, or just before, they start to flower. You can cut plants by hand, or by using a trimmer, brush cutter, or mower. Cutting before flowering not only prevents the cover crop from going to seed, but also stops the plant from taking up nutrients from the soil to store in its seed. Once plants have been cut, incorporate the plants into the soil (using a shovel, pitch fork or rototiller) where they can more readily decompose. Allow approximately two to three weeks for the cover crop to decompose before planting into the soil.

Cover Crop Sowing


Seeding Rate Per 100 sq. ft.
(10’ x 10’ Garden)
Does This Plant Fix Nitrogen? Growth Rate Primary Uses/
Buckwheat Spring,
2 lb No Fast Is easily worked into the soil.

Attracts pollinators and beneficial insects.

Re-seeds prolifically.
DO NOT allow to go to seed.

½ lb Yes Medium Grows better in high pH soils than other clovers.
Oats Late Summer, Early Fall 4 lb No Medium Likes well drained soils.

Dies over the winter.

Makes a good choice in areas to be worked early the following spring.

Early Fall
5 lb Yes Fast Can outcompete many weeds.
Fall 1 lb No Fast Is easily worked into the soil.
Fall 4 lb No Fast Easy to grow.

Grows fast.

Can be planted late in the season.

Late Summer, Early Fall 1 lb No Fast Easy to grow.
Late Summer, Fall 2 lb No Fast Needs fertile soil.

Does not like low pH soils.

Table 1. Recommended cover crops and green manures for the home vegetable garden.*

*Information compiled from Johnny Select Seed Company and Cornell University Department of Horticulture

For more information on using cover crops and green manures in the home vegetable garden: Contact your county Extension agent.

Top Ornamental Crabapples for Wisconsin

Malus 'Prairie Maid' in flower
Malus ‘Prairie Maid’ in flower

Why grow crabapples? Ornamental crabapples are very popular, small to medium-sized ornamental trees suitable for urban environments. There are more than 650 different cultivars of crabapples with a variety of leaf, flower, and fruit colors, fruit sizes, and growth forms. Crabapples are tolerant to a wide range of soil conditions, as long as they are well drained. It is important when selecting crabapples to not only select for ornamental value, but also disease resistance. In addition, it is best to select a crabapple with small-sized fruit that persist throughout the winter. The list below provides information on some of the most ornamental, disease resistant crabapples available for landscaping in Wisconsin. Cultivars listed below are considered proven performers. This list is by no means comprehensive and new introductions are currently being evaluated.

White flowers/red fruits:

Latin Name
(Common Name)
Height Description
Malus baccata ‘Jackii’ 30′ fragrant flowers; persistent fruit
Malus sargentii 6-8′ mounded, shrubby form; wide spreading; fragrant flowers
Malus sargentii ‘Tina’ 4-5′ dwarf form; wide-spreading; slow grower
Malus x zumi var. calocarpa 15-25′ broad form; fragrant flowers that are pink in bud; persistent fruit
Malus ‘Jewelcole’
Red Jewel™)
15-18′ rounded form; persistent fruit
Malus ‘Sutyzam’
(Sugar Tyme™)
15-20′ oval to rounded form; fragrant flowers
MalusAdirondack’ 15-20′ upright growth habit to oval; dark green leaves

White flowers/yellow fruits:

Latin Name
(Common Name)
Height Description
Malus ‘Ormiston Roy’ 20-25′ rounded form; fruit turns yellow-orange in late fall

Malus ‘Hargozam’
(Harvest Gold®)

20′ upright form; persistent, golden fruit

Red or Pink flowers/red to maroon fruits:

Latin Name
(Common Name)
Height Description
Malus ‘Prairifire’ 15-20′ rounded form; purple, shiny bark; purple leaves; dark purplish-red flowers
Malus ‘Prairie Maid’ 15′ purple to green foliage; deep pink flowers; cherry-red fruit
Malus sargentii ‘Candymint’ 8-10′ pink flowers with white centers; red fruit

Weeping form:

Latin Name
(Common Name)
Height Description
Malus ‘Coral Cascade’ 15′ semi-weeping form; pinkish-white flowers; persistent, orange fruit
Malus ‘Louisa’ 10-15′ graceful, weeping form; pink flowers; yellow fruit
Malus ‘Manbeck Weeper’ (Anne E.™) 10′ wide-spreading weeper; persistent fruit
Malus ‘Molazam’ (Molten Lava®) 10-15′ horizontal weeper; white flowers; orange fruit

For more information on crabapples: See UW-Extension bulletins A1616, A2173, A2598, and University of Wisconsin Garden Facts X1007, X1009B, or contact your county Extension agent.

Summer Flowering Trees, Shrubs, and Vines

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Hydrangea paniculata 'Grandiflora' (PeeGee hydrangea) in summer bloom.
Hydrangea paniculata ‘Grandiflora’ (PeeGee hydrangea) in summer bloom.



May Showers Bring Summer Flowers:  Most gardeners think that spring is the time of year when woody plants flower.  However, many trees and shrubs flower from late spring to late summer.  Wisconsin homeowners can choose from a variety of plants listed below to insure continual bloom throughout most of the growing season.



Flowering Trees:

Latin Name Common Name Height Description
* Catalpa speciosa Northern catalpa 50-60′ large leaves; large, white flowers in late June
* Cladrastis lutea yellowwood 30-40′ vase-shaped; white, fragrant flowers in mid June
Cornus alternifolia pagoda dogwood 15′ native; creamy, fragrant flowers in mid June; blue fruit
* Cotinus obovatus American smoketree 20-30′ tall; greenish, smoky flowers in late June
* Crataegus phaenopyrum Washington hawthorn 25′ tall; thorny; white flowers in June; red fruit
 * Maackia amurensis amur maackia 20-30′ tall; smooth olive bark; white flowers in July
** Magnolia sieboldii Oyama magnolia 15′ tall; white, fragrant flowers in late June; may be hard to find
** Stewartia pseudocamellia Japanese stewartia 15-20′ tall; exfoliating bark; white flowers in July, acid
Syringa reticulata ‘Ivory Silk’ Japanese tree lilac 15-25′ tall; oval shape; creamy flowers in mid June
* Syringa pekinense Pekin lilac 15-20′ tall; exfoliating bark; creamy-white flowers in mid June
Tilia cordata little leaf linden 50-60′ tall; pyramidal shape; small, fragrant flowers in June


No asterisk indicates cold hardy to zone 3.
* Indicates hardy to zone 4. In colder areas, such as zone 3 (northern WI), the plant may die back.
** Indicates hardy to zone 5. In colder areas, such as zone 3 and 4 (central WI), the plant will die back.

Flowering Shrubs:

Latin Name Common Name Height Description
* Aesculus parviflora bottlebrush buckeye 8′ suckering; showy, white flowers in July
** Buddleja davidii butterfly bush 5′ tall; dies back; fragrant flowers from July to fall; marginally hardy; needs protection
** Calycanthus floridus Carolina allspice 6-8′ tall; fragrant, brownish-maroon flowers in mid June; marginally hardy
** Caryopteris x clandonensis blue mist spirea 3′ tall; dies back; blue flowers in Aug. to Sept.; marginally hardy
* Cephalanthus occidentalis buttonbush 8′ tall; native shrub; coarse texture; creamy-white, globular flowers in July
* Clethra alnifolia summersweet clethra 4-8′ 4-8′ tall; fragrant, pinkish flowers in late July to Aug.; acid soil
Cornus alba Tatarian dogwood 6-8′ tall; red stems; white, flat-topped flowers in June
Cornus racemosa gray dogwood 6-10′ tall; native; white, flat-topped flowers in June; white fruit
Cornus stolonifera redosier dogwood 6-8′ tall; native; red stems; white, flat-topped flowers in June
* Cotinus coggygria smokebush 10-15′ tall; some with red new growth; pinkish, smoky flowers in July
Diervilla lonicera bush honeysuckle 3′ x tall; native; suckering; small, yellow flowers in early July
* Genista tinctoria common woodwaxen 2-3′ tall; bright, yellow flowers in late June to July
** Hibiscus syriacus rose-of-Sharon 8′ large flowers in July to Aug.; marginally hardy; dies back
Hydrangea arborescens ‘Annabelle’ Annabelle hydrangea 4′ tall; suckering; large, white flowers in July
Hydrangea macrophylla ‘All Summer Beauty’ bigleaf hydrangea 4′ tall; large, pink flowers in July-Aug.
Hydrangea paniculata panicle hydrangea 6-15′ tall; large, white flowers Aug. to Sept. that turn brown
* Hypericum kalmianum Kalm St. Johnswort 2-3′ tall; native; showy bark; yellow flowers in July to Aug.
* Lespedeza bicolor shrub bushclover 4′ tall; dieback shrub; reddish-purple flowers in July-Aug.
* Ligustrum obtusifolium var. regelianum Regel’s border privet 4′ tall; hedge; white flowers in late June
** Perovskia atriplicifolia Russian-sage 3-4′ tall; gray-green leaves; violet-blue flowers in Aug.; dies back
Potentilla fruticosa potentilla 3′ tall; native; yellow to white flowers from late June to fall
* Rosa hybrids many to choose from; many colors; choose ones for disease resistance
Rosa rubrifolia redleaf rose 4-6′ tall; suckering; red-purple leaves; pink flowers in June; red hips
Rosa rugosa rugosa rose 4-5′ tall; fragrant flowers in many colors from late June to fall; large hips
* Rosa setigera prairie rose 6′ native; suckering; pale pink flowers in early July; small hips
* Rosa pimpinellifolia Scotch rose 3-4′ tall; suckering; yellow, white, or pink flowers in June to July
Rosa virginiana Virginia rose 4′ tall; suckering; red stems; pink flowers in June; red hips
Sambucus canadensis American elderberry 8′ tall; native; suckering; white flowers in June; black fruit
Sorbaria sorbifolia Ural falsespirea 5′ tall; suckering; large, fuzzy, white flowers in July
Spiraea x billiardii Billiard spirea 6′ tall; suckering; large, dense, rose flowers in July to Aug.
Spiraea fritschiana Korean spirea 4′ tall; blue-green leaves;  large, white flowers in late June
Spiraea japonica Japanese spirea 2-4′ tall; many cultivars, white or pink flowers in June to Aug.
Tamarix ramosissima tamarisk 8′ tall; fine texture; pink flowers in late June to Aug.
** Vitex agnus-castus chastetree 3-5′ tall; dies back; blue flowers in late July to Aug.; marginally hardy
* Weigela x ‘Red Prince’ Red Prince weigela 5′ red flowers in late May and again in summer
* Yucca filamentosa yucca 2-3′ tall; evergreen; sword-like leaves; large white flowers in July


No asterisk indicates cold hardy to zone 3.
* Indicates hardy to zone 4. In colder areas, such as zone 3 (northern WI), the plant may die back.
** Indicates hardy to zone 5. In colder areas, such as zone 3 and 4 (central WI), the plant will die back.

Flowering and Colorful Foliage Vines:

Latin Name Common Name Height Description
* Actinidia kolomikta kolomikta actinidia grown mainly for foliage with white to pink mottling
* Actinidia polygama silvervine actinidia grown mainly for foliage with silvery mottling
* Aristolochia macrophylla Dutchman’s pipe grown mainly for large leaves; small, pipe shaped flowers
* Campsis radicans trumpet creeper vigorous; fast growing; large, orange flowers from July-Aug.
* Clematis hybrids many colors and sizes of flowers, early to late summer; some with showy seed heads
** Clematis tangutica golden clematis yellow, bell-shaped flowers in late summer; showy seedheads
* Clematis terniflora sweet autumn clematis very showy, fragrant, white flowers in early Sept.
* Clematis texensis scarlet clematis urn-shaped, nodding, scarlet to pink flowers in late June to fall
* Clematis viticella Italian clematis white, violet, red, or mauve flowers in midsummer
* Hydrangea petiolaris climbing hydrangea large, lacy, white flowers in late June; exfoliating bark
* Lonicera x brownii ‘Dropmore Scarlet’ Dropmore scarlet honeysuckle summer, tubular, scarlet flowers
* Lonicera x heckrottii goldflame honeysuckle dark pink and yellow, tubular, fragrant, summer flowers
* Lonicera sempervirens trumpet honeysuckle trumpet shaped, orange-scarlet or yellow flowers in July
* Polygonum aubertii silver fleece vine fragrant, white, lacy flowers in summer; fast grower, marginal
* Rosa x ‘Henry Kelsey’ Henry Kelsey rose climbing; arching; semi-double, red flowers in summer
* Rosa x ‘William Baffin’ William Baffin rose climbing; semi-double, deep-pink flowers in summer
** Wisteria frutescens American wisteria fragrant, lilac or white, 6″ long flowers in July; marginally hardy
* Wisteria macrostachys Kentucky wisteria lavender or white, 8″ long flowers in June


No asterisk indicates cold hardy to zone 3.
* Indicates hardy to zone 4. In colder areas, such as zone 3 (northern WI), the plant may die back.
** Indicates hardy to zone 5. In colder areas, such as zone 3 and 4 (central WI), the plant will die back.

For more information on woody plants: See UW-Extension bulletins A2865, A3067, G1609, A1771, and University of Wisconsin Garden Facts X1012, X1014, X1015, or contact your County Extension Agent.

Thanks to Sharon Morrisey, Brian Hudelson, Ed Hasselkus, and Amy Sausen for reviewing this document.

Siberian Squill

What is Siberian squill? Siberian squill (Scilla sibirica) is a member of the lily family (Liliaceae) and one of the first of the spring-flowering bulbs to brighten the landscape in early spring. It is one of more than 100 species in the genus Scilla that are native to Europe, Africa, and Asia. While Siberian squill’s name suggests that the plant originated in Siberia, it actually is native to other areas of Russia and elsewhere in Eurasia. Siberian squill has been cultivated since 1796, and is grown throughout USDA zones 2 to 8.

Siberian squill produces whorls of grass-like leaves and nodding, bright blue flowers.
Siberian squill produces whorls of grass-like leaves and nodding, bright blue flowers.

Siberian squill produces dark green, grass-like leaves that emerge from the ground in early spring. Soon thereafter, one or more arching flower stalks (up to six inches in length) are produced from the center of the rosette of foliage. Each flower stalk supports one to three nodding flowers of intense royal blue. Individual flowers are up to an inch across, with six blue “petals” (technically three petals and three sepals) with a single dark blue vein running down the middle, and blue anthers (male reproductive structures). Blossoms have a pleasant floral fragrance, and are attractive to bees and other pollinating insects. They last for approximately two to three weeks and are very tolerant of snow and freezing temperatures. Fertilized flowers form green, bumpy, and roundish seed capsules. As they mature, the capsules turn brown, eventually splitting to release numerous reddish-brown seeds. By early summer, foliage of Siberian squill dies down, and the plants’ small round bulbs, covered in a loose dark tunic, remain dormant in the soil until the next spring. Fortunately, Siberian squill is not a preferred food of voles, chipmunks, rabbits or deer.

There are only a few named varieties of Siberian squill.

  • ‘Spring Beauty’ has somewhat larger flowers and sturdier stems.
  • ‘Alba’ has pure white flowers.
  • Scilla sibirica taurica has bright blue flowers.

Where do I get Siberian squill? While Siberian squill spreads very easily by seed once established in a garden or landscape, this ornamental is best initially established by planting bulbs. Select bulbs that are large, firm (not soft), and free of gashes and other blemishes. Avoid bulbs showing any signs of fungal growth (e.g., colorful masses of spores) on their surfaces.

How do I grow Siberian squill? Siberian squill does best in full to partial sun, in soils with good drainage and an abundance of organic matter. In wet soils, crown and bulb rots can be a problem. Plant bulbs in the fall, placing them two to three inches deep, and two to four inches apart. Because of the ephemeral nature of Siberian squill foliage, this bulb can be grown easily in sunny lawns. To plant Siberian squill in turf, scatter the bulbs randomly over the lawn. Punch a hole in the sod, using an auger, dibble or other implement (e.g., a cordless drill with a large bit), wherever a bulb has fallen. Place a bulb (pointed side up) at the bottom of each hole and fill the hole with soil. Once plants have finished flowering in the spring, wait for the foliage to begin to die before mowing the lawn. If you must use herbicides for weed control, do so in the fall (not the spring) when the bulbs are dormant.

How do I use Siberian squill most effectively in my garden? Plant Siberian squill in masses (preferably approximately 20 bulbs per square foot) and loose drifts. Some experts recommend never planting fewer than 100 bulbs. Siberian squill can also be used throughout flowerbeds, along walkways and paths, in herb or rock gardens, and interspersed in perennial gardens.

Siberian squill is spectacular when planted in large masses or drifts.
Siberian squill is spectacular when planted in large masses or drifts.

Siberian squill mixes well with other early bloomers, such as giant crocus (Crocus vernus), yellow winter aconite (Eranthis hyemalis), snowdrops (Galanthus spp.) striped squill (Puschkinia libanitica), light blue glory-of-the-snow (Chionodoxa spp. – see University of Wisconsin Garden Facts XHT1169), early daffodils (Narcissus spp.), including ‘Tête-à-Tête’, ‘Jetfire’, and ‘Dutch Master’, early tulips (Tulipa spp.), and Virginia bluebells (Mertensia virginica). Adding the blue of Siberian squill to a garden can cool and soften the effect of the bright and intense color of many tulips and daffodils. If space is limited in a garden, Siberian squill bulbs can even be planted on top of deeper-planted spring bulbs such as daffodils and tulips. Siberian squill can also be planted between later-emerging perennials such as ferns, hostas or Lamium where dying bulb foliage will be hidden by the perennials as they leaf out.

Although Siberian squill requires sun to thrive, it is particularly attractive when allowed to naturalize under deciduous trees and shrubs. Leafless branches allow the bulbs ample exposure to the sun when they are actively growing. By the time the trees and shrubs have leafed out, Siberian squill plants are starting to go, or have already gone, dormant and thus do not require as much light. Keep in mind however that because Siberian squill so readily naturalizes, it may become invasive in some situations.

Finally, Siberian squill is one of the best squills for forcing. See University of Wisconsin Garden Facts XHT1144 (“Forcing Bulbs”) for details on how to use this plant to brighten the indoors during the winter.

For more information on Siberian squill: Contact your county Extension agent.

Safely Using Produce from Flooded Gardens

After flooding occurs, gardeners often raise questions about the safety of consuming produce from gardens that were under water for a day or two. How concerned gardeners have to be about using garden produce after a flood depends, to a large degree, on how “clean” the flood water was or whether it was likely to have been contaminated with sewage, river or creek water, farm run-off, or industrial pollutants. The most conservative answer — one that eliminates any and all risks — is that gardeners should discard all produce that was touched by flood water. However, if flooding occurs early, there will typically be weeks left in the growing season, and gardeners will likely wish to salvage some crops. The following are tips for considering what can be salvaged and what must be discarded from a flooded garden.

Flooded produce must be evaluated carefully before it is consumed.
Flooded produce must be evaluated carefully before it is consumed.

Produce can be cooked to ensure safety. This is the best choice if anything that was touched by flood water will be served to those most at risk for serious consequences from microbial food-borne illnesses: young children, the elderly, pregnant women and those with compromised immune systems. Note that cooking will not eliminate the risk posed by industrial pollutants.

Discard all produce that is normally consumed uncooked (raw), including all leafy vegetables such as lettuce or spinach, regardless of how mature the plants are. It is not possible to clean these crops as they have many ridges and crevices that could contain contaminated silt or bacteria. All soft fruits that are ready to harvest, such as strawberries or raspberries, should also be discarded unless they can be cooked; they too are impossible to thoroughly clean and cannot be safely consumed raw.

Other produce may be salvaged depending on the crop and how far along it is in the growing season. In general, any produce where the edible part was directly touched by flood water presents a potential risk to health if consumed. This includes produce that was submerged or splashed by flood water. The ability to salvage crops that will be eaten raw with minimal risk depends on the source of the flood water, time to harvest, and whether potential contamination will have been internalized into the plant tissue. One starting point for evaluating the safety of produce from flooded gardens is the National Organic Program (NOP) guidance to farmers wishing to harvest produce from soil fertilized with non-composted manure. The NOP requires a 90-day period before harvesting edible material from plants grown in soil fertilized with non-composted manure, but where the manure has not come in contact with the edible material. NOP standards require a 120-day period before harvest of edible plant material that had direct contact with non-composted manure. Research suggests that contamination from non-composted manure should present a more significant health risk than contamination from flood waters.

Early season crops that are to be harvested within a few weeks after a flood, and that remain above flood waters should be safe to eat if cooked or peeled. Examine any produce carefully before harvest. If it is soft, cracked, bruised, or has open fissures where contamination might have entered, throw it out. Intact produce can be eaten, but should be rinsed with clear tap water (DO NOT use soap) followed by a brief soak (2 minutes) in a weak chlorine solution of two tablespoons bleach in a gallon of water. Finally, rinse the produce in cool, clean tap water. Peel or cook these items thoroughly before eating. Take care to prevent cross contamination in the kitchen. Change the bleach solution if the water is no longer clean.

Plants where fruits have set (tomatoes) or where flowers are evident (broccoli/cauliflower) at the time of flooding present an undefined risk. Before consuming these crops raw, consider the source of the flood water, the time since contamination, and the health of the tissue. Always discard any tissue that is bruised, cracked or otherwise blemished. Washing fresh produce with clear water, followed by a brief soak in a dilute bleach solution (see above) and then rinsing before eating or peeling will help to reduce any remaining risk.

Vegetables, such as tomatoes, produced from flowers that form after flooding has occurred can be safely used.
Vegetables, such as tomatoes, produced from flowers that form after flooding has occurred can be safely used.

Underground vegetables such as beets, carrots and potatoes that are still early in their growth (at least four to eight weeks from harvest) should be safe if allowed to grow to maturity. Root crops (i.e. new potatoes) that will be consumed within a month after flooding should be washed, rinsed and sanitized as directed above before cooking thoroughly. Note that beets may be peeled after cooking, if desired.

Melons and other fruits that will be eaten raw should not be consumed. Recent food-borne illness outbreaks linked to melons suggest that these low-acid fruits may not be safe even if surface-sanitized.

Lateseason vegetables that result from flowers produced on growth that develops after flood waters subside should be safe. This group of vegetables includes tomatoes, peppers, eggplants, squash, cucumbers, and other similar vegetables. To increase safety, cook these vegetables thoroughly, or at least wash them well and peel them, if possible, before eating.

Flooddamaged garden produce that is otherwise unfit for eating should not be canned or otherwise preserved. Garden produce that would be safe to consume after washing, sanitizing and cooking (see above) may be safely canned. Because the low temperature of home dehydrators does not destroy high numbers of bacteria, do not attempt to dehydrate produce from flooded gardens.

Never sell produce from a flooddamaged garden at a farm market or farm stand until you are sure that all contamination has been removed from the garden, usually a period of at least one month after the last incidence of flooding. Check with the Division of Food Safety of the Department of Agriculture, Trade, and Consumer Protection at (608) 224-4665 if you have questions about market sales of garden-flooded produce.

For more information on safely using produce from flooded gardens: Contact your county Extension agent.

Safely Using Manure in the Garden

Many vegetable gardeners swear by the benefits of manure as a fertilizer. Adding manure to soil improves the soil’s texture and water-holding capacity while providing nutrients needed by growing plants.

Proper use of non-composted manure as a fertilizer is important in preventing contamination of root crops (such as carrots) with harmful microbes.
Proper use of non-composted manure as a fertilizer is important in preventing contamination of root crops (such as carrots) with harmful microbes.

Unfortunately, fresh manure can also contain bacteria that can contaminate vegetables and cause human disease. Proper composting will kill these bacteria, but steps must be taken to ensure that the manure gets hot enough for a sufficient time during composting. Storing manure in a pile will cause some death of disease-causing bacteria, but is not regarded as a reliable way to destroy them. The risk of bacterial contamination from manure is serious enough that USDA National Organic Program (NOP) rules specifically address when non-composted manure can be applied to soil used for vegetable production. The NOP rules state that if vegetables have edible parts that might contact the soil (either directly or via rain/irrigation splash), then manure must be applied at least 120 days before harvest. For a crop like sweet corn, where the edible portion is not exposed to soil, the limit is 90 days before harvest. In Wisconsin, 120 days can cover most of the vegetable growing season, so growers may be tempted to apply fresh manure in the spring, even though harvest will be less than 120 days away.

Can a shorter manure application-to-harvest interval be safely used by Wisconsin vegetable growers? Probably not. Recent results from my own research indicate that applying fresh cow manure 90, 100, or 110 days prior to harvest may significantly increase the likelihood that Eschericia coli (i.e., E. coli) bacteria from manure will contaminate vegetables. My research also found that the interval between manure application and planting is even more important than the fertilization-to-harvest interval. This is because vegetables are most sensitive to bacterial contamination just after sprouting.

What are the safest options for Wisconsin vegetable growers? I recommend three possible ways to apply manure to vegetable-growing soils in Wisconsin. Growers should either 1) use properly composted or otherwise sterilized manure (from a commercial source or your yard) for application during the current growing season, 2) apply non-composted manure in the fall before crops are planted the next spring, or 3) apply non-composted manure as soon as possible in the spring and then only plant fall-season crops in the fertilized soil. For example, apply manure in April, plant radishes in August, and harvest radishes in September. If growers use option 3, great care should be taken to keep manure away from spring and summer-season crops. Avoid problems from runoff, and from tracking manure from one part of the field to another on boots or tools.

What about pet wastes? Pet wastes (as well as human wastes) should not be used to fertilize soil in which vegetables are grown.

Do the practices discussed above guarantee safety? Fresh produce is never risk-free. Even if proper fertilization procedures are followed, birds and other wildlife can still transfer bacteria to your crops. Washing produce will reduce the risk of contamination, but will not ensure safety. Thorough cooking of vegetables usually destroys disease-causing bacteria. If you use good manure-handling practices in your garden, the health benefits of a produce-rich diet are far greater than the risk of food-borne illness.

For more information on proper manure use and composting: Contact your county Extension agent.

Reducing Soil pH

Is your soil pH too high? Probably not, although the popular press urges most gardeners to question whether their garden soil pH is ‘right’. Only a soil test for pH can indicate whether the pH is ‘right’, and ‘right ‘ really depends on the plant you want to grow and the natural pH of your soil. Turf, vegetables, annual ornamentals and most perennial ornamentals are very tolerant of a wide range of soil pH levels, and acidifying soil is generally not necessary or recommended. Blueberries, rhododendrons and azaleas however, are quite intolerant of alkaline conditions and the soil pH must be maintained at 5.5 or less in order to grow them successfully.

High soil pH can lead to a yellowing of tissue between leaf veins.
High soil pH can lead to a yellowing of tissue between leaf veins.

To determine current soil pH, start with a soil test. For soils having a pH of less than 7.5, you should be able to add a soil amendment (e.g., some form of sulfur) and successfully lower pH, if recommended. If soils have a pH above 7.5, adding a soil amendment will probably not reduce pH much because of the ‘free’ calcium carbonate or marl present in these soils. This is an unfortunate characteristic of soils in some parts of Wisconsin. In these soils, consider growing plant species more tolerant of high pH conditions.

Soil pH can be reduced most effectively by adding elemental sulfur, aluminum sulfate or sulfuric acid. The choice of which material to use depends on how fast you hope the pH will change and the type/size of plant experiencing the deficiency. Sulfuric acid (commonly available as battery acid) is fast acting, but is very dangerous, and its use by home gardeners is not recommended. Green industry professionals however, occasionally use sulfuric acid to reduce soil pH around large, established specimen trees. Aluminum sulfate and elemental sulfur can be safely used by homeowners. Aluminum sulfate is faster acting than elemental sulfur because it is very soluble. The advantage of elemental sulfur is that it is more economical, particularly if a large area is to be treated.

In general, it is best to reduce soil pH before planting sensitive landscape ornamentals, rather than attempting to reduce soil pH after plants have become established. Use about 4 to 6 lb. of aluminum sulfate per plant for most medium- and fine-textured Wisconsin soils in order to decrease soil pH by about one unit. If elemental sulfur is applied, decrease the total recommended application by one-sixth. One pound of aluminum sulfate or elemental sulfur is equal to about 2 cups.

As an example, suppose your initial soil pH is 7.4 and you want to plant blueberries which require a pH of no higher than 5.5. You should apply about 8 to 12 lb. (16 to 24 cups) aluminum sulfate, or 1⅓ to 2 lb. (2⅔ to 4 cups) elemental sulfur per plant. Be sure to delay planting for about one month after application to avoid root burn.

If plants are already established, use a top-dress application limited to about 1 lb. (2 cups) aluminum sulfate or 1/6 lb. (⅓ cup) elemental sulfur per typical landscape plant. Lightly incorporate the aluminum sulfate or elemental sulfur into the soil, or water-in well. Repeat applications monthly until the total recommended amount of aluminum sulfate or elemental sulfur has been added. Because lowering soil pH is a very slow process, have the soil pH checked about three months after each application to determine if additional applications will be needed. Several applications may be needed on some soils before the soil pH shows any significant change.

Applying certain fertilizers, such as ammonium-containing nitrogen fertilizers like ammonium sulfate, urea or ammonium sulfate, can help maintain acid soil conditions, but these fertilizers will probably not be effective in significantly reducing soil pH. The ammonium in these products reacts in the soil to help maintain the lowered pH. Keep in mind however, that many fertilizer products such as potassium sulfate and gypsum will not effectively reduce soil pH.

Peat moss and certain other organic materials such as pine needles are a good source of organic carbon and can be used to help reduce soil pH. However these organic materials are very slow acting and may not be effective for causing large soil pH changes. Try adding a one to two inch layer of these organic materials and incorporate them into the top six to 12 inches of soil before planting. Afterwards, check the pH. Addition of aluminum sulfate will probably still be needed to ensure that the soil pH is reduced enough for successful gardening.

For more information on reducing soil pH: Contact your county Extension agent.