Testing Xeriscape Groundcovers

TESTING XERISCAPE GROUNDCOVERS TO REPLACE LAWN AREAS

Whether this turns out to be a drought year or not, the idea of conserving water is probably as vital to our future as educating our children. As long as the human population grows, the demand on our water reserves will continue to rise, forcing eventual water-rationing even if the supply stays the same. And as we have seen this year, we can’t count on a bountiful supply from the heavens. Ten years ago these ideas, and the fact that my own water source is a very low-producing well, got me to thinking about how much water we use in Colorado to water our lawns. We know that xeriscape plants use less water than bluegrass, so why couldn’t we use large areas of certain low-water plants to replace lawn, which could greatly reduce the demand on our valuable water? In order to test a variety of xeriscape plants that might function as replacements for Kentucky Bluegrass, I built a 104′ x 6′ demonstration garden which will be on the 2002 Xeriscape Garden Tour, taking place in Boulder June 29th and 30th.

No plant tolerates sports and children’s play as well as turf grasses and thankfully there are now better and more xeric turf alternatives to Kentucky Bluegrass. However, many landscapes have large expanses of bluegrass that get only occasional foot traffic, often only when they are mowed. At the same time our American yards are often so big that tearing out the grass and putting in lush gardens would require the care of a full-time gardener, and most of us can’t afford the time or the money for that. But what if we could plant big patches of xeric ground covers that would use half or even a quarter of the water of bluegrass, be less time-consuming to maintain than a perennial garden, and could still give the satisfactions of flowering, winter interest and personal character? I decided to test at least 60 ground covers that might be successful in replacing a lawn.

I knew it might take years of experimenting to find the best ground covers to take the place of turf grass, so I sent a survey to about 25 professionals in our rich community of horticulturists and gardeners. I asked them to name 5 or 10 ground covers using these criteria:

  1. Needs half the water and half the fertilizer of bluegrass.
  2. Has few if any pest problems.
  3. Grows densely so as not to require much weeding once established.
  4. Looks good in most seasons.
  5. Withstands occasional foot traffic.
  6. Is not hard to weed out of perennials. I was very pleased to get excellent suggestions from Jim Knopf, Panayoti and Gwen Kelaidis, Lauren Springer, Bob Howard, Marcia Tatroe, Homer Hill, Barbara Hyde, Alison Peck, Mike Woods and others. This was in 1993.

I realized that even the best plants wouldn’t fare well with the bindweed that invades everything on my land, so I decided to build short concrete walls to make it easier to keep out the bindweed and to separate the varieties of groundcovers. These beds contained sections for 66 different varieties, providing a 3’x3′ area for most of them, to show what a good-sized patch would look like. This was completed in 1996.

The next year, Paul Lander of the Boulder Water Conservation Department came out to see my xeriscape rock garden in July and asked about the empty concrete beds. I explained my project and he suggested that I apply for a city grant. Such a demonstration garden has the potential to save the city of Boulder a lot of water, so I was granted enough money to pay for a good drip irrigation system, an occasional truck-load of water and two water meters which could confirm the water-requirements of the ground covers.

For the next three years circumstances of my personal life denied me the possibility of carrying on, but finally the irrigation system went in and I planted in the fall of 2000 and the spring of 2001. Ten years after it was begun, the project is nearly completed. For the next few years I will replant some, replace a few and keep taking photos and making evaluation reports. Many of these ground covers look very promising. However, the real proof will be when enough people plant them in large areas that we will be able to judge their usefulness in replacing thirsty turf grass.

Here are portraits and reviews of five of the best performers.

Geranium cantebrigiense and Ger.cant.’Biokovo’: the excellent plantsman, Dermod Downs, brought my attention to this plant years ago. What really caught my attention was that I planted it first in the wrong place, in a very sunny, dry and inhospitable location; and even though it suffered through the summers, it wouldn’t die and always bloomed very nicely in the spring. When I moved it to dry shade, it thrived; and it has done well in full sun in my xeriscape demonstration bed. The foliage is light green, very fragrant when rubbed, dense enough to suppress weeds, and it turns red in the fall. It grows 8″ high and can spread 24″ or more in diameter. The flowers are a medium pink, and in the selection ‘Biokovo’ they are a light blush pink. This hardy geranium is a winner.

Delosperma ‘John Proffitt’ (Table Mountain): this variety resembles Delosperma cooperi but is an improvement. The foliage is more substantial, dense, turgid in winter and attractively tinged purple, growing 2—3″ high and 10—20″ in diameter. The flowers are a purple-red to lavender-fuschia with a creamy eye, and they have a very long bloom time. ‘John Proffitt’ is also reported to be more cold hardy than D. cooperi. It is a Plant Select winner for 2002 and though it is supposed to require moderate watering, has done well in my demonstration garden. It is beginning to bloom in May and could be the best performing ice plant I have tried so far.

Achillea serbica: this Serbian creeping yarrow is not like the aggressive rhizomatous Achillea millefolium varieties. Whereas it can spread 18″ in diameter, it is not a thug and can easily be weeded out if necessary. The foliage is very beautiful with narrow, cut-leaf, silver, “evergreen” leaves making a dense mat 4—6″ high. The ½” flowers are pure white with a yellowish eye and are somewhat daisy-like. They are held on 8″ stems and smother the foliage with a blanket of bloom in May/June. The plant is drought tolerant, but may get smaller in desperately dry conditions. Some people think Achillea serbica is a subspecies of Greek Yarrow, Achillea ageratifolia; others believe the two are identical. It makes a fine silver ground cover around red, yellow or blue-flowering upright perennials.

Penstemon pinifolius: Pineleaf Penstemon is quite different from most of the penstemons I know. It is neither a creeping mat-forming type, nor a tall spikey type. Instead P. pinifolius has pine needle-like leaves and has a shrubby habit. The evergreen quality of its winter foliage is outstanding. Often evergreen leaves burn in our scorching Colorado winter sun, but not those of Pineleaf Penstemon. There are several different forms. The most common is 10—15″ tall and 24″ wide; a more compact form is 6—10″ high and 12″ wide. Both have narrow, orange-red tubular flowers that bloom profusely over a long period. In addition it is a long-lived penstemon. There is a yellow-flowered form, ‘Mersea Yellow’ which is similar in size to the compact version, and should be cutting-grown. Penstemon pinifolius enjoys low water conditions with good drainage, but will not tolerate foot traffic.

Woolly Thyme was one of several thymes that performed well in my demonstration garden. It is the well-known gray, ½” high woolly foliage that we see so often. It has a good fragrance, seldom flowers and can get to 3′ in diameter (more often 18″). It works well between flagstones, though it can become too large if the traffic doesn’t wear it down. It’s evergreen foliage looks good in a large area, or planted around perennials. It is known to die out in patches from variously hypothesized causes like lack of water, too much water, not enough aeration in the soil, etc. Its botanical name is Thymus pseudolanguinosus and there is a Thymus languinosus which is, of course, very similar but which is not supposed to rot out as readily. I am also testing this variety.

If you think this article is incomplete, you’re right. A demonstration project must be seen not just heard. However if you go on the 2002 Xeriscape Garden Tour June 29 and 30, I will be giving a guided tour of this demonstration garden at 2 PM both Saturday and Sunday, and you will be able to see all 66 varieties. I’m sure there will be other good gardens to see on the tour as well.

Copyright 2003 by Mikl Brawner