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Ground covers offer gardeners exciting alternatives to turf. Increasingly, garden-savvy homeowners are digging up traditional bluegrass and replacing it with a stunning array of sprawling, low-growing plants.
Ground covers are gaining popularity for a number of reasons. Many homeowners have been unsuccessful in maintaining lawns in boggy or shady areas while others are tired of risking life and limb mowing steep slopes. Some empty nesters, whose children no longer need a play area, feel that they've outgrown the usefulness of their lawns. Xeriscape gardeners want to replace thirsty bluegrass with more drought tolerant plants, and plant-lovers are looking forward to exhibiting a variety of distinctive ground covers in their landscapes. Finally, people suffering from spring fever are sick of looking at the brown mat of their winter turf. They can hardly wait to plant groundcovers that feature enchanting winter color and texture.
Spring is an excellent time to establish a ground cover. The cooler and slightly wetter weather of the season can help young plants get off to a great start, and local nurseries are fully stocked with a tempting variety of suitable plants in economical, small-sized pots.
However, before going shopping it is wise to do some preparation and planning. First, control the weeds in the proposed planting area. Many ground covers are advertised as plants that "keep out" weeds, but this typically only means that once the plant is mature its foliage becomes thick enough to compete with weed seeds. It does not mean that the newly planted ground cover can magically eradicate robust, existing weeds. After dealing with any weeds, prepare the planting site. Take the time to improve your soil and notice how much light and water your site receives.
Then, think about the qualities that you require from a ground cover. How tall would you like the plant to be, and how much area would you like to cover? Ground covers range in height from half an inch or so to twelve inches tall and their widths can vary enormously. In fact, some groundcover plants can be quite monstrous, spreading so aggressively that they become invasive. Even if you are covering a lot of ground, you might want to avoid bullies like Bishop's weed Aegopodium podagraria, Sweet woodruff Galium odoratum, or Creeping buttercup Ranunculus repens.
Does the plant need to withstand foot traffic? If so, consider Irish or Scotch moss, Sagina subulata, or the many varieties of creeping thyme. Deep green Irish moss and bright chartreuse Scotch moss stay evergreen in winter and feature small white flowers in late spring. In our sunny climate, Sagina subulata requires some shade and water to thrive. In contrast, thyme is great for those hot, sunny areas and boasts marvelous fragrance. Woolly thyme, Thymus pseudoanuginosus, has tiny fuzzy gray leaves that smell of Thanksgiving dinner while many other varieties of creeping thyme have greener leaves with a lemony aroma. Thyme flowers are pink or lavender in summer.
Do you want your groundcover to be evergreen or provide other winter interest? Creeping junipers, Juniperus horizontalis, are exceptionally valuable for the color that they provide to the winter landscape. Blue varieties often keep better color if they are planted in shadier sites. The spiny leaves of Creeping Oregon grape, Mahonia repens, take on a deep burgundy color in wintertime while the succulent foliage of sun-loving Yellow ice plant, Delosperma nubigenum turns a delicious, glowing raspberry.
Are flowers important to you, or would you like a certain color of foliage? Many ground covers, like most perennial plants, only flower for a month or two in spring or summer. Almost nothing can compare to the beautiful blooms of creeping phlox, Phlox subulata, in early spring, but will you enjoy the needle-like leaves for the summer months that follow? If not, maybe you should consider one of the more prostrate varieties of dianthus. Dianthus deltoides ‘Brilliant' and ‘Zing Rose' feature rosy red flowers in May and June followed by deep green mat-like foliage. While Dianthus grantianopolitanus "Firewitch" is a happy combination of neon pink flowers and short, powdery blue foliage. If you love true blue flowers, plant one of the many varieties of creeping veronica. Turkish veronica, veronica liwanensis, has tiny, shiny green leaves, and Woolly veronica, Veronica pectinata, which keeps its leaves most winters, resembles a miniature prostrate juniper. For exciting fuschia-colored blooms, plant Poppy mallow, Callirhoe involucrata. If you are looking for gray foliage, consider the finely cut leaves of Snow-in-summer, cerastium tomentosum or Silver mound sage, Artemisia schmidtiana. Plant some Sedum x ‘Vera Jameson' in sun or one of the Heucheras like ‘Palace Purple' or ‘Chocolate Ruffles' in shade, if burgundy or chocolate foliage is more to your taste.
Finally as you shop the wonderful world of ground covers, calculate how much time you want to spend caring for your plants. Although many ground covers are low maintenance, no ground cover is no-maintenance. While evergreens usually don't require too much upkeep, plants that produce flowers or fruit often demand more work to keep them looking good. Still, with a garden of ground covers, the chore of mowing your lawn might become a distant memory.
Q: My lilac bush hasn't flowered in three or four years. What could be wrong?
A: Several things can influence a lilac's bloom. First, lilacs need at least six hours of sunlight a day to bloom with real vigor. Also, if you prune your lilacs, you must prune them right after they are done blooming or you will cut off next year's buds. Finally, if your lilacs are planted next to a lawn that receives a lot of high nitrogen fertilizer, the nitrogen will promote the shrub's leaf growth rather than bloom.
Q: What gardening zone is Fort Collins?
A: Fort Collins is generally considered to be in USDA hardiness zone 5. Plants that are listed as growing in zone 5 or lower should be able to survive our winters. Plants labeled as zone 6 or higher should be considered annuals here. These plants will probably not make it through our winters. Remember, however, that areas protected by structures could be a zone higher and areas subjected to cold drying winds could be a zone lower.
Q: I love the way Aspen trees look in the mountains, but down on the plains many of them seem to look different. Why?
A: Aspen, Populus tremuloides, grow best at elevations above 7,000 feet. Aspen also prefer moist soil that drains well. At lower elevations, aspens are prone to a distressing array of insects and diseases.
Q: Last year I bought a hibiscus at a local nursery that was labeled perennial, but now it just looks like a dead stick in the ground. Is it alive?
A: Perennial hibiscus is very slow to wake up in the spring. Since the plants often get to be quite large, this late dormancy often surprises gardeners who are growing hibiscus for the first time. Have patience; your hibiscus is probably still sleeping but very much alive.
Forsythia can be one of our most spectacular spring shrubs. It was first brought to England from China by Robert Fortune and named for a Scottish Gardener, William Forsyth, who helped found the Royal Horticulture Society of England.
Crabgrass, foxtail, barnyard grass and goosegrass are annual grasses that are weeds when they are growing in your lawn. The seeds of these grasses germinate when the SOIL temperature reaches 55 – 60 degrees. Apply a preemergent herbicide in April – depending on the weather and the soil temperature. This herbicide will not control weedy grasses after the seed has germinated and started to form leaves. Do not apply before seeding a new lawn or laying sod.
Bare root roses can be planted during April. Select a site in full sun with well-drained soil. Before planting, prune any damaged or broken roots and after planting prune the canes 1/4 inch above a bud, leaving 6" – 8" of cane. Cover the entire plant with loose, moist soil to keep the canes from drying out and to protect them from frost damage. The covering can be left on for 2 to 7 weeks – until the danger of frost has past – and will have to be removed carefully to avoid damaging the new tender growth.
Pinyon pine is an excellent tree to add to your low-water landscape plans. It will grow 15 to 25 feet tall and about as wide. It is extremely drought tolerant and grows well with our normal amount of precipitation. Be sure and water regularly for the first few years after planting until the root system gets established. Do not plant Pinyon pine in a turf area that is getting regular irrigation as it does not want supplemental water.
Add spring color to your garden with a perennial other than the usual tulips and daffodils. Try Primula denticulata - the "drumstick Primrose". It's available in pinks and purples and flowers during April and early May – even during our unpredictable spring snow storms.
Cool season vegetables like cabbage, broccoli and kohlrabi, lettuce and spinach, leeks and onions, parsley, peas, radishes and turnips are very hardy and can be seeded into the ground now.
The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.
Fact Sheets are available at the Larimer County Extension Office, 1525 Blue Spruce Drive, Fort Collins, Colorado, telephone (970) 498-6000, or contact us by e-mail at larimer@coop.ext.colostate.edu
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