Category Archives: General Horticulture/Weeds

Cupflower

What is cupflower? Nierembergia, commonly known as cupflower, is a genus of tender, heat-loving perennials in the nightshade family (Solanaceae) that is valued for its long blooming period. The genus, which is native to Argentina, is named for Juan Eusebio Nieremberg, a 17th century Spanish Jesuit theologian and naturalist. The taxonomy of Nierembergia is somewhat confused, and the species names for cupflower have been variously listed as N. caerulea, N. frutescens, N. hippomanica or N. scoparia. While hardy only in USDA zones 7 through 10, cupflower can easily be grown as an annual in colder climates.

Cupflower produces mounds of blue or white, star-shaped, saucer-like flowers.
Cupflower produces mounds of blue or white, star-shaped, saucer-like flowers.

Cupflower plants form neat, compact, spreading mounds that are approximately 12 to 15 inches in diameter. Plants have multiple stems with fine-textured, stiff, linear, ½ inch-long leaves, and. eventually become covered with one inch diameter, white or bluish-purple star-shaped, saucer-like flowers with lemon yellow centers. The color of cupflower blossoms does not fade even in the brightest sun. There are several varieties of cupflower that may be available at greenhouses and garden centers in your area.

  • ‘Blue Mountain’ grows six to nine inches tall and has azure-blue flowers.
  • ‘Mont Blanc’ grows six inches tall and 12 inches wide and is a profuse bloomer with small, brilliant white flowers. This variety was an All-America Selection winner in 1993.
  • ‘Purple Robe’ grows six to eight inches tall and has violet-blue flowers. This variety was an AAS winner in 1942.
  • ‘Starry Eyes’ grows 10 to 16 inches tall and 15 to 18 inches wide. This variety has white flowers with pale lavender highlights.
  • ‘Summer Splash Compact Blue’ grows 10 to 14 inches tall and has large, blue flowers.
  • ‘Summer Splash Compact White’ grows 10 to 14 inches tall and has large, white flowers.
  • ‘White Robe’ is an early blooming variety that grows six to eight inches tall and approximately eight inches wide, and has white flowers.
White cupflower combines nicely in the garden with tall blue salvia and pink globe amaranth.
White cupflower combines nicely in the garden with tall blue salvia and pink globe amaranth.

Where do I get cupflower plants? Cupflower plants can be purchased at most commercial greenhouses and garden centers. Alternatively, you can start cupflower plants from seed. Sow seeds indoors eight to 10 weeks before the predicted date of last frost in your area. Barely cover the seeds at planting. Seeds should germinate within two to three weeks if grown at 70°F. Keep the soil slightly moist until the seeds germinate, then water the seedlings only after the soil begins to dry out. Young plants will grow very slowly, but will grow more quickly once transplanted outdoors.

How do I grow cupflower in my garden? Transplant purchased cupflower plants or homegrown cupflower seedlings outdoors after the last spring frost. Be sure to harden off the plants before transplanting. Place plants six to 12 inches apart in organically rich, well-drained soil in full sun. Mulch the plants to help retain moisture and keep the soil cool. Cupflower is drought tolerant once established, typically does not have severe insect pest or disease problems, and usually is not bothered by deer. Stem cuttings can be taken in late summer and rooted to grow plants indoors over the winter.

How do I use cupflower most effectly in my garden? Use cupflower as an edging, and in borders, rock gardens, or containers, including hanging baskets and window boxes. White varieties combine nicely with tall blue salvia (Salvia spp.) and pink globe amaranth (Gomphrena globosa – see University of Wisconsin Garden Facts XHT1171). Cupflower thrives in hot environments, such as along walkways or walls that reflect heat, where it can spill out to soften sharp landscape edges.

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

Creeping Charlie

What is creeping Charlie? Creeping Charlie (Glechoma hederacea) is an herbaceous perennial plant that spreads by seed and by creeping stems (called stolons) that grow along the ground. Creeping Charlie was introduced into North America from Europe by early settlers who thought it would be a good groundcover for shade. A variegated form of the plant is sometimes used in hanging baskets. Creeping Charlie is also known as ground ivy, gill-on-the-ground, and creeping Jenny.

What does creeping Charlie look like? Creeping Charlie produces bright green, round or kidney-shaped leaves that have scalloped edges. The leaves are produced opposite each other on square (i.e., four-sided), creeping stems that root at the nodes. In spring, small, bluish-purple, funnel-shaped flowers appear. When the plant is crushed, it produces a strong mint-like odor. Creeping Charlie is often confused with henbit (Lamium amplexicaule), which is a winter annual.

Creeping Charlie produces kidney-shaped leaves with scalloped edges on creeping stems (left) and small, bluish-purple, funnel-shaped flowers (right).
Creeping Charlie produces kidney-shaped leaves with scalloped edges on creeping stems (left) and small, bluish-purple, funnel-shaped flowers (right).

How can I control creeping Charlie? Creeping Charlie thrives in moist, shady spots such as under trees and shrubs, and along the north sides of buildings. Altering these moist, shady conditions can discourage growth of creeping Charlie. If possible, improve soil drainage or water less frequently to dry the soil, and prune trees to open the canopy and increase light levels. If creeping Charlie is invading a thin lawn, try to improve turf health and density to get weeds under control. This can be accomplished by mowing regularly (to a height of two to three and one-half inches), fertilizing and watering appropriately, and overseeding in the fall. Also, make sure to grow the most suitable type of turfgrass for the location (e.g., plant shade tolerant turfgrass varieties under trees). See University of Wisconsin-Extension Bulletin A3700 for additional information on lawn establishment and maintenance. Alternatively, consider removing grass and growing shade-loving plants such as vinca, English ivy, pachysandra or hosta that compete well with weeds. In areas where creeping Charlie has become established, try removing plants by hand. This is the control method of choice in vegetable or flower gardens. However, this may not be a viable option in heavily infested areas, as the extensive spreading stems of creeping Charlie can be difficult to completely remove. Once plants are pulled, make sure to dispose of the plants in such a way that they cannot re-root. An alternative (and oftentimes more effective) means of controlling creeping Charlie is with a postemergence broadleaf herbicide. The best choice for homeowners is a weed killer that contains triclopyr. This active ingredient is found in many commercially available homeowner lawn care products, oftentimes in combination with other herbicides such as dicamba (3, 6-dichloro-o-anisic acid), 2,4-D (2, 4 dichlorophenoxyacetic acid) and mecoprop or MCPP [2-(2-methly-4-chlorophenoxy) propionic acid]. Products containing 2,4-DP can also provide adequate control. All of the products listed above can be used for treating lawns, but cannot be used in vegetable or flower gardens as many common vegetables and ornamentals are broadleaf plants that are very susceptible to these herbicides. In areas of a lawn with an extensive creeping Charlie infestation, it may be easier to use a broad-spectrum herbicide (e.g., glyphosate) to kill all of the vegetation in the area and then reseed the lawn.

When using an herbicide for

Creeping Charlie rapidly invades lawns, crowding out and replacing turf.
Creeping Charlie rapidly invades lawns, crowding out and replacing turf.

creeping Charlie control, be sure to read and follow all label instructions of the product that you select to ensure that you use the product in the safest and most effective manner possible. A general rule of thumb is to make applications when temperatures are in the mid 60s to low 80s, there is no rain expected for 24 hours following application, and there is little or no wind. DO NOT mow the treated area for several days before and after an herbicide application. Dicamba, triclopyr, MCPP, 2,4-D or 2,4-DP applications for creeping Charlie control should be made when plants are actively growing. A mid to late autumn herbicide application (after the first frost) is often particularly effective. During this period, plants are drawing nutrients from their leaves and into their roots for storage over the winter, and herbicides are more effectively moved into the roots as well, resulting in better control. A second application can be made in the fall if needed. Herbicide applications can also be made in the spring, but should be timed to correspond to creeping Charlie’s blooming period (typically April to June). Plants are more sensitive to herbicides during this time. Again, a second application may be necessary to obtain adequate control. Note that any herbicide containing dicamba should not be used in a given area more than twice per year. Finally, borax has been touted as an organic control for creeping Charlie. However, research at both the University of Wisconsin and Iowa State University has shown that borax does not provide long-term control of creeping Charlie, and can injure turf and other plants, causing stunting and yellowing. Thus borax is not recommended for creeping Charlie (or other broadleaf weed) control.

For more information on creeping Charlie: Contact your county Extension agent.

Ageratum

What is ageratum?  The genus Ageratum includes approximately 60 species of annual and perennial herbs and shrubs in the aster family (Asteraceae) that are all native to Central and South America.  One species that is commonly used as a bedding plant, Ageratum houstonianum, is from Mexico, and is named after William Houston (1695-1733), a Scottish physician who collected the first ageratum plants.  The name ageratum is derived from the Greek “a geras”, meaning non-aging and refers to the long-lasting nature of ageratum flowers.

Ageratum plants have soft, fuzzy flowers that can be blue, pink, lavendar or white.
Ageratum plants have soft, fuzzy flowers that can be blue, pink, lavendar or white.

Wild species of ageratum can grow to over two feet in height and typically reseed themselves liberally.  Varieties offered by nurseries and garden centers however are almost all hybrids that are more compact and better behaved.  Commercially available ageratum cultivars grow in neat mounds, flowering from late spring through fall.  They are one of the more dependable flowering annuals. Ageratum plants have oval to heart-shaped leaves that are up to two inches long.  Flowers of ageratum are typically some shade of blue, but can be pink, lavender or white.  The soft, fuzzy flowers are dainty and feathery, often delightfully fragrant, and usually cover plants completely.  Each flower cluster consists of five to 15 tubular florets. There are many different cultivars of ageratum, including attractive dwarf, tufted plants as well as tall, upright types that can be used as cut flowers.  Most cultivars are propagated from seed, and are predominantly F1 hybrids (i.e., offspring from crosses of two plants of closely related species or strains of a single species).

  • ‘Blue Blazer’ was the first commercial F1 ageratum hybrid.  This cultivar has better plant uniformity and vigor, and blooms earlier than open-pollinated cultivars.
  • ‘Blue Danube’ has compact six to eight-inch-tall plants covered with mid-blue flowers.  This cultivar is one of the best varieties for uniformity, earliness and general performance.
  • ‘Blue Horizon’ is an F1 hybrid that grows 30 inches tall and produces three-inch clusters of purplish-blue flowers on long stems.  This cultivar is great as a cut flower.
  • ‘Blue Mink’ is an open-pollinated cultivar that grows 12 inches tall and has powder-blue flowers.
  • ‘Hawaii’ is a series of F1 hybrids, each of which is dwarf (up to eight inches tall) and compact, with soft pink, royal blue or pure white flowers.  Members in this series flower earlier and longer than other varieties.
  • ‘Pinky’ produces salmon pink flowers on bushy and compact eight-inch-tall plants.
  • ‘Purple Fields’ is an F1 hybrid that produces compact, mounded plants that spread up to 12 inches across.  This cultivar is covered with unusual, purple flowers.
  • ‘Summer Snow’ is an F1 hybrid with fluffy white flowers;
  • ‘Trinidad’ has a unique, early-blooming blend of white, blue, violet and pink flowers on six-inch-tall plants.

Where do I get ageratum?  Ageratum transplants can be purchased at local garden centers.  However, ageratum can also be grown very easily from seed.  Start ageratum seeds eight to 10 weeks before you would like to transplant them into your garden.  Surface sow the seeds, barely covering them with vermiculite or potting mix.  Be sure that the seeds receive light to stimulate germination.  Germination usually takes seven to 21 days.  Transplant the seedlings into trays or pots when they are large enough to handle.  Move potted plants outside to harden off and transplant them into the garden when all risk of frost has passed.

Blue-flowered ageratum pairs well in the garden with yellow-flowered ornamentals.
Blue-flowered ageratum pairs well in the garden with yellow-flowered ornamentals.

How do I grow ageratum?  Transplant ageratum plants six to eight inches apart in a sunny spot.  Ageratum prefers a moist, well drained soil, but will also tolerate dry conditions.  Ageratum plants generally do not have insect or disease problems, although spider mites can be an issue, especially in hot, dry weather.  On most cultivars, old flowerheads turn brown and remain on the plants.  Deadhead regularly to improve the appearance of plants and prolong blooming.  Some cultivars are self-cleaning (i.e., the flowers fall off naturally).  Ageratum plants are sensitive to cold temperatures, so be sure to cover plants on cold nights in the fall to extend their survival.

How do I use ageratum most effectively in my garden?  Because of their short stature, most varieties of ageratum are best used for edging or borders of flowerbeds, in rock gardens, or in containers.  Blue varieties are particularly attractive when combined in the garden with pink-flowering plants.  Combine soft blue-flowering varieties of ageratum with pink begonias (Begonia spp.) for a low, pastel ground cover, or mass them with short yellow marigolds (Tagetes spp.) or cockscomb (Celosia spp.) for greater contrast.  Taller blue varieties of ageratum go well with yellow cosmos (Cosmos sulphureus).  Also try mixing the powder blue varieties with white petunias (Petunia spp.), lamb’s ear (Stachys spp.) or dark blue lobelia (Lobelia spp.).

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

African Violets

What are African violets? African violets (Saintpaulia spp.) are popular flowering houseplants in the Gesneriad family (Gesneriaceae), native to Tanzania in East Africa. Their compact forms make them ideal for use on tabletops, windowsills, and hanging baskets.

The blossoms of African violets can provide year-round color for your home.
The blossoms of African violets can provide year-round
color for your home.

There are many varieties of African violets, including trailing and miniature varieties. African violets usually form rosettes of rounded, velvety leaves with scalloped edges on short fleshy leaf stems. Leaves are often dark green with red-tinted undersides, and sometimes are variegated. Small clusters of flowers surround the foliage in shades of pink, red, white, violet, purple, blue and bicolor. Flowers can be single, double, semi-double, fringed, star-shaped, and Geneva (edged in white). African violets have a reputation for being difficult to grow, but under suitable conditions they will thrive, producing long blooming flowers throughout much of the year.

How do I care for African violets? African violets prefer locations with bright, indirect light.  In a south or west exposure, plants need to be protected from direct sunlight during peak hours, or foliage will burn.  If African violets do not form flower buds, they are likely not receiving enough light and should be moved to a sunnier location, or placed under artificial light.  In particular, supplemental fluorescent or full spectrum lighting may be necessary in winter months to encourage year-round flowering.  Position lights eight to 12 inches above plants, allowing 14 to 16 hours of light per day.  African violets prefer 70-75°F days and 60-65°F nights.  Place plants in a location with good air circulation, but keep them away from cold windows and cool drafts as sudden changes in temperature can harm the plants. African violets should be watered moderately from spring until fall, allowing soil to dry slightly between waterings.  Reduce water slightly in winter months.  Bottom water plants to avoid water splash on foliage, as cold water can damage leaves causing brown spots.  Fill saucers with warm water, allow plants to soak up water for approximately 30 minutes, and drain off excess water once the soil is sufficiently moist.  African violets are extremely susceptible to crown rots, which can rapidly kill the plants.  To prevent crown rots, avoid overwatering, avoid watering directly into the crown, and avoid watering at night. African violets grow best when potted in a well-drained, soilless potting mix or pre-packaged African violet mix.  Keep plants slightly pot-bound to encourage flowering.  Use a pot that is approximately one half the width of the plant’s spread.  When plants are in flower, apply a specially formulated African violet fertilizer once a month, following the label instructions of whatever fertilizer you select.  Remove older flowers and leaves as they begin to wither to improve the aesthetics of the plant, and to prevent problems with Botrytis cinerea, the gray mold fungus (see University of Wisconsin Garden Facts X1122).

For more information on African violets:  Contact your county Extension agent.