Groundcovers Project in its 18th Year

In 1993 I sent a survey to 29 local horticulturists to get their suggestions on the best groundcovers for a demonstration project we were planning at Harlequin’s Gardens. I asked them to list 5-10 groundcovers that could be used to replace bluegrass in low traffic areas, that would need a quarter to a half the water of bluegrass, have few pests and diseases, would grow densely to limit weeds, would look good in most seasons and would not be invasive in gardens. The survey was typed on a typewriter and most of the replies were hand-written. People did drive cars back then. But that was a long time ago and I had a lot to learn.

         Recommendations came from Homer Hill, Panayoti Kelaidis, Lauren Springer (Ogden), Barbara Hyde, Marcia Tatroe, Jim Knopf, Alison Peck and others. They were a big help. Harlequin’s was pretty wild back then so I built the 6′ x 106′ demo garden with 4″ thick cement walls, that divided the space into 6’x6′ cells that were quartered. The cement was supposed to keep out the bindweed and each 3’x3′ mini-cell was to be planted with one groundcover.

         We really didn’t have the money to complete the project so it got off to a slow start. By 1997 the beds were made but the irrigation system was not. Paul Lander from the City of Boulder Water Conservation Center, got wind of the project and saw its value and so gave us a grant to buy the Netafim Drip System and two water meters to measure water use. Half of the groundcovers were to be given 50% of normal Kentucky bluegrass irrigation and half were given only 25% of bluegrass irrigation.  The idea was that the garden would show the public low-water alternatives to bluegrass, not necessarily to replace lawns, but to support successful xeriscape gardens and save water.

         Finally, the garden was planted in 2000 and 2001 with 68 different groundcovers. They were just getting established when the big drought of 2002 hit. Some plants that we thought could handle drought died or looked bad. Some plants that were growing very dry in my xeriscape garden, rotted in the  walled cells. Some plants like garden yarrow got too tall to qualify as a groundcover. Some plants really needed more shade. And some have survived drought, heat, hail and rabbits. Over the 18 years, we have removed, added and experimented with many different varieties.

          We did learn a lot about groundcovers. We learned that just because they are perennial does not mean they are eternal. So if a groundcover thrives for 10 years and then dies, it may be worth replanting. Also very shallow-rooted evergreen groundcovers, like thymes, that make great thyme lawns in England, can burn up in our Colorado winter sun and so do better in part shade or with winter watering. And another thing is that groundcover monocultures are really not any better than bluegrass monocultures. Gwen Kelaidis Moore who wrote Hardy Succulents, wrote a great article on the “Persian Carpet Effect” which was her idea of mixing low ground covers with different textures and flowers to create a carpet-like mosaic. This approach is visually more interesting, there is resilience in diversity, and if one species dies or is eaten, it is not a disaster.

         Groundcovers can be used in many ways. A lawn area can be greatly reduced by removing the turf from a 6′-8′ wide border around the lawn, putting in a 6″ deep edging to contain the grass and planting low-water shrubs, perennials and/or groundcovers. Groundcovers can be used around shrubs and larger perennials to provide a living mulch and a longer season of color. Evergreen groundcovers add winter interest and will continue to nourish the symbiotic mycorrhizae during the winter. Groundcovers, especially slow-growing ones make good specimen plants, and look good and often prosper growing among rocks. Groundcovers are also useful along walks and paths where we don’t want large plants hanging over the walkway.

         Groundcover maintenance, of course, varies with the variety. In general, keep well weeded, especially when they are small, remove old flowers and dead material in early spring, and topdress with a ¼” of fine compost in fall and/or spring. A light fertilization with an organic fertilizer may be beneficial. Water needs vary, but water twice as much in July and once a month in dry winters. Even though groundcovers are sometimes called “stepables”, some, like iceplants don’t tolerate being stepped on and if traffic is frequent, stones or pavers may be needed. A fine mulch is often helpful to get groundcovers established.

         Warning: there are groundcovers that are so invasive that I do not recommend them: Aegopodium podagraria-Snow on the Mountain,  Duchesnia indica-Mock Strawberry, Pink Panda Strawberry (cross between strawberry and Potentilla palustris); Glechoma hederacea-Ground Ivy, Ranunculus repens-Creeping Buttercup

         Here are some of the groundcovers that prospered in our display garden. The complete list can be found at

         Delosperma Lesotho Pink Iceplant: tight, evergreen foliage 1″ high x 16″ wide with magenta pink flowers for a month in midspring. Very durable and cold-hardy. Good for bees. At least 5 years.

         Delosperma Kelaidis Iceplant (Mesa Verde): 2″ lighter green foliage that is winter –hardy, vigorous, compact. The light salmon-pink flowers are long-blooming. It seems more heat-tolerant than other iceplants. Original planting

         Sempervivum arachnoideum- Hen and Chicks: the cobweb forms are shorter and tighter. Most are low-water, sun and shade tolerant, great between rocks, and can even exclude bindweed with some weeding. Original.     Erigeron glaucus ‘Olga’: daisy-like flowers on 6″-12″ stems above 3″-4″dense, dark green rosettes; pale lavender rays and yellow centers bloom June to November. Not a true spreading groundcover, but is dense enough to exclude most weeds. Original Planting-17 years.

         Herniaria glabra-Rupturewort, Green Carpet: bright green 2″-3″ tall foliage that spreads to 18″-24″, has one deep taproot, is more drought tolerant than surface-rooting thyme. The flowers are not showy. Takes foot traffic, better between flagstones in sun than thyme. Original planting.

         Iberis-Candytuft: only the low-growing forms like I. saxatilis, Iberis from Dedal Dag and Little Gem can be considered groundcovers. Tough, evergreen foliage with pure white flowers. Original planting.

         Aubrieta deltoidea-Purple Gem: dense gray-green mat 4″-6″ high and 12+” wide. Blooms purple in spring. Although tough and low-water, it needs dead-heading after bloom and a good watering or it will crash. Original

         Globularia cordifolia-Globe Daisy: tiny, deep green leathery foliage that is evergreen, growing slow but steadily. Great between rocks or for a small area.  It is durable and xeric. After 17 years it needs to be replanted.

         Eriogonum umbellatum ‘Kannah Creek’: a great selection of our native Sulfur Flower. Xeric perennial is 4″-6″ high x 16″ wide with evergreen foliage that turns mahogany in winter. The flowers are yellow pom-poms. Original.

         Phlox subulata ‘Boothman’s’: a more durable Creeping Phlox with vivid lavender blue flowers with a dark purple eye. It spreads 18″-24″ and is 3″ high. The leaves are needle-like and evergreen. Original planting.

         Waldsteinia ternata-Barren Strawberry: attractive, strawberry-like leaves 3″ high and 12″ wide. It blooms a deep yellow in early spring. This plant would be much better in some shade. Still- Original planting

         Geranium cant. ‘Biokovo’: this spreading Hardy Geranium is one of the best. The plants grow densely to 8″ high, 16+” wide, bloom a long time with pale pink flowers. The foliage turns red in fall. Tough. Original planting

         Cerastium candidissimum: a dwarf Snow in Summer with dense, very silvery foliage that looks great all year; beautiful white flowers that do not flop after blooming. Needs more water the first year. Original.

         Dianthus gratianopolitanus: Cheddar Pink Dianthus-the species from which cultivars like Fire Witch were bred. Excellent, tough, dense, durable, evergreen groundcover. Single, pink, very fragrant flowers. Original planting

         Veronica liwanensis-Turkish Veronica: 1″-2″ high evergreen mat to 24″ wide with small glossy green leaves and cobalt blue flowers in spring. It is fairly xeric, but could use winter watering. Excellent. Original planting

         Veronicas: pectinata, oltensis and prostrata are also very good.

         Groundcovers offer many benefits and some advantages over turf. Most of them flower, which provide beauty as well as nectar and pollen for the beneficial insects. Their variety of textures provides interest when they are not flowering. They reduce evaporation, keep soil temperatures cooler in summer and reduce weeding. Some groundcovers are evergreen or have attractive winter color, and quite a few are successful in shade where most turf grass does poorly. Groundcovers are easier to maintain in narrow strips than turf, and do not require regular mowing. And many are more water-conserving than most turf grasses.  The tremendous variety of textures and colors offer rich opportunities for creativity and pairing with other plants.