November 2015
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News for Norther Colorado and the world

Saturday, November 28, 2015

Master Gardeners, ground cover and more


By: Dick Christensen
Colorado State University Extension Master Gardener in Larimer County

Turfgrass is arguably Colorado’s best-known ground cover, but it is not ideally suited to all locations. Deep shade, steep slopes, and areas with exposed tree roots may be good places to establish other plants, such as low-growing perennial ground covers.

From a purely practical point of view, ground covers offer alternatives to turf in hard-to-mow sites and reduce the need for watering and other maintenance. Ground covers conserve moisture, maintain even soil temperatures, and stabilize soil in erosion-prone areas. In garden design, ground covers can create visual pathways to help direct foot traffic and can help link ornamental plants or provide transitions among outdoor spaces. Many ground covers spread quickly to form dense plantings, which can help to inhibit weeds.


When selecting ground covers, consider their spread, height, location, function, foliage texture, and color. Since no single species of plant works for every landscape situation, pay attention to soil conditions, light, and moisture requirements. Some plants prefer partial shade, while others thrive in deep shade or full sun; a few tolerate a wide variety of light conditions. The most effective selections are chosen with an eye for how plant sizes relate to the intimacy or expanse of particular landscape sites. When ground cover will be used to prevent soil erosion on a steep slope, it should have an extensive root system and vigorous growth habit. Some ground covers do not withstand excessive foot traffic; before planting anything, create a walkway through areas intended for pedestrians.

Soil Preparation

A key to successfully establishing ground covers is proper soil preparation. Before planting, eliminate weeds and turf from the area. For large areas, use a sod-stripping machine to clear turf. For weed control, consider a glyphosate herbicide or soil solarization. The process of solarizing uses the heat of the summer sun to raise soil temperatures high enough to kill harmful organisms and seeds in the ground. Solarize soil by laying strong transparent plastic over cleared and moistened soil. Seal the edges with soil and leave plastic in place for four to six weeks.

Improve the soil’s tilth (texture and richness) before planting ground covers. Since many ground covers spread by offshoots or runners, they are more apt to fill in quickly when soil has good aeration and drainage. Before planting, incorporate two to four cubic yards of compost or other quality organic materials, such as compost, leaf mold, or well-rotted manure into each 1,000 square-foot area. Work soil to a depth of six to eight inches (a rototiller may be helpful). Fertilizer can be mixed into the soil at the same time that other amendments are incorporated. Choose a fertilizer formulated for your plants. Always carefully follow directions with herbicides and fertilizers, and consider having your soil tested for more specific information.


Before you plant, calculate how many plants are needed. Arranging and spacing depends on a plant’s growth characteristics. Space plants so that the distance between them is about equal to their maximum width. If plants are very slow growing, space them slightly closer. Spaced properly, most ground covers will spread and cover the soil surface by the third growing season. Plant them in staggered rows, not straight lines, to achieve faster coverage and space plants so they will develop a uniformly covered area.

When establishing a ground cover under existing trees, choose shallow-rooted plants. Since the majority of fibrous tree roots are found in the top twelve inches of soil, prepare soil for planting only two or three inches deep to minimize disturbance of roots and possible damage to trees. Most ground covers can be planted any time during the growing season, but spring or fall is preferred.

Water and Mulch

Water plants thoroughly after planting to settle the soil. Spread two to three inches of organic mulch. Pull mulch about six inches away from plant stems. Maintain even soil moisture until plants resume vigorous growth¬—usually in one to two growing seasons. It will take a year or longer for groundcover to fill in. When initially planted, groundcover will require frequent, deep watering to help it develop a healthy root system and to encourage spreading. Gradually reduce how often you water. Some groundcovers are xeric and require little water once established.

Weed Control and Maintenance

Weeding, re-mulching, feeding, and maintenance watering will be the main requirements for new ground-cover plantings. Weeding will need to be done periodically during this time. Weeds may become a problem in a ground cover planting if not managed properly. Pull weeds as they appear and replace mulch as needed. Once groundcover is established, you will need to weed only occasionally. Using a light layer of mulch helps to reduce weeds and retain moisture. Fertilize as needed.

Ground covers for hot, dry, sunny exposures.

Sedum has succulent leaves and does well in sunny locations. Many varieties exist; two popular selections are Dragon’s Blood and Tricolor. Hen and Chicks is another succulent but grow in tight rosette-type leaves. There are many to choose form in a variety of colors and sizes. Lamb’s Ear has furry, gray leaves that resemble its namesake. Many cultivars exist including white flowering forms, plants with shorter growth habits, and plants that do not bloom as much. Partridge Feather has finely-cut, silvery-white foliage. Ice Plant grows in a dense mat and requires very little maintenance. In winter the foliage turns red.

Ground covers for sun to part shade

Plumbago has attractive green foliage that turns red in fall with cornflower-blue flowers. Thyme and Veronica are popular choices for in between stone walkways. Thyme varieties (not culinary types) include several dense, low-growing plants. They come in many varieties and colors. A few are citrus-scented. Veronica is one of the largest flowering plant groups. Turkish veronica is low growing with dark green leaves.

Selected ground covers for part-to-deep shade.

Ajuga or Carpet Bugle include a range of spreading, mat-like plants, two to three inches high with flowers in assorted colors and forms. Lily-of-the-Valley has nodding, fragrant flowers in late spring. There are dozens of varieties of Hosta, which are primarily grown for their foliage. They range in size from less than four inches across to more than two and a half feet across. Hostas are typically green, although some have variegated leaves with blue, gold, and cream. These plants grow best in moist soil and deep shade. Periwinkle or Vinca is available in several colorful varieties. It has few pests or diseases.

Use with caution. Snow-on-the-Mountain or Bishop’s Goutweed, Sweet Woodruff, Snow-in-Summer, Creeping Jenny or Moneywort, and certain other groundcovers can grow very vigorously. Keep out for the word “aggressive” on plant tags. For these plants, consider “corralling” them in concrete or in a confined location with some type of edging to keep them under control.

Fortunately, there are many ground covers from which to choose. For a complete list of Colorado ground covers refer to CSU Extension Fact Sheets #7.230 and #7.400 available online from

Gardening Tips

By: Anne Wuerslin
Colorado State University Extension Master Gardener in Larimer County

Consider shopping end of summer sales at nurseries and greenhouses for healthy perennials and woody plants. If planted by mid-September, these plants will establish a root system and be advanced come spring. Be sure to water in winter.

Take clippings of geraniums, coleus, begonias and other tender annuals that can be grown indoors as houseplants. Use rooting hormone on the cuttings and plant in a soilless potting mix that includes vermiculite. Wait until plants develop two healthy sets of new leaves before transplanting.

As pumpkin, squash and gourd vines mature, pinch off emerging blossoms and cut back on watering. This will put more energy into set fruit.

Gardening Q&As

By: Trudi Manuel
Colorado State University Extension Master Gardener in Larimer County

Question: “My honeysuckle is covered in aphids! Could I use a horticultural oil to control these insects?”

Answer: Oils affect insects differently, but their main advantage is coating the body of the insect, which results in suffocation since insects “breathe” through their body. Horticultural oils are refined petroleum products and can be found under names such as Sunspray, Scalecide, Trilogy and Volck, among others. Using summer oil treatments on foliage to control aphids, whiteflies and mites is an acceptable practice. Spider mites and young stages of scale can be also be controlled by applying oils during growing season. During the dormant season, horticultural oils can be used to control aphids that cause leaf curl. Oils can also be useful against powdery mildew. A big benefit of using oils is that they have few risks for people and beneficial insects, however, always read the label carefully and only apply as directed. For more information, visit and read CSU Extension Fact Sheet #5.569, “Insect Control: Horticultural Oils.”

The authors have received training through Colorado State University Extension’s Master Gardener program and are a Master Gardener volunteers for Larimer County

Larimer County is a county-based outreach of Colorado State University Extension providing information you can trust to deal with current issues in agriculture, horticulture, nutrition and food safety, 4-H, small acreage, money management and parenting. For more information about CSU Extension, Larimer County, telephone (970) 498-6000 or visit

Visit PlantTalk Colorado ™ for fast answers to your gardening questions! PlantTalk is a cooperation between Colorado State University Extension, GreenCo and Denver Botanic Gardens.

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