Xeriscape? Are you kidding? With all the rain we’ve been getting, isn’t the drought over?
As I understand our current water situation, water restrictions are still in effect for the Denver area, Colorado Springs has had a very dry spring until July and is under water restrictions, the Western Slope has been dry, New Mexico has been dry until July; and Montana and South Dakota are having severe droughts. What this means is that the wonderful moist season we are enjoying in the Denver area depends on ephemeral conditions we cannot count on. In addition, much of our water comes from the Western Slope where weather patterns can be quite different from our own, so even if our gardens are getting watered, it doesn’t mean our reservoirs will be full. We live in a semi-arid environment and water conservation and xeriscaping will be increasingly important as our population grows, especially if global warming increases our temperatures.
Therefore, in spite of the fact that we’ve had a cool, moist July, I’m going to talk about plants that need little water and will provide color in July, usually our hottest, dryest month. Many drought tolerant plants bloom in the spring when there is more moisture and because of this, many xeriscapes look rather colorless in July. This is especially true when gardeners buy blooming plants in the spring and then give up gardening when it gets hot. Here are some suggestions for xeriscape plants to bloom and carry on the color when we need it the most.
One of the most colorful summer-blooming natives is Gaillardia aristata, whose bold red and yellow Indian Blanket flowers bloom generously even with little or no water and care. It grows 12”-24” high and wide and often self-sows. The seedlings can be mostly yellow or strongly red. Cultivated varieties are also excellent: Gaillardia x grandiflora ‘Burgundy’ has entirely wine-red daisy-like flowers, Goblin is a dwarf 10”-15” tall with red and yellow flowers.
Verbena wrightii is another native that blooms all summer. It has clusters of phlox-like flowers ranging from rose to purple. These bloom on stems that sprawl, standing up at the ends. They make very showy, long-blooming plants 10”—20” high and 24” wide. Other verbenas for our area are V. bipinnatifida, also with rose to purple flowers and the non-native “Homestead Purple”, 8” x 24” with bright lavender-purple flowers .
Many dianthus varieties are spring blooming, but there are some notable exceptions. The delicate narrow blades of Dianthus petraeus noeanus (couldn’t we just call this one “petra”?) looks so much like grass in early spring that it often gets accidently weeded out, but in July its elegant, lacy fringed white flowers wave lightly over the grassy dome. Not only are the flowers showy, but their fragrance is exquisite; more like Jasmine than the clovy sweetness characteristic of most dianthus varieties. Dianthus nardiformis is another great summer bloomer, making perfect airy domes of bright pink flowers that bloom for weeks and weeks. Dianthus giganteus has clusters of pink or white flowers atop 2’-3’ tall stalks.
One of the few summer-blooming shrubs is the native Leadplant, Amorpha canescens. It has an open form, 2’-4’ high and wide with ferny gray-green leaves and short spikes of showy violet-purple flowers. This is not a long show, but so lovely that it is becoming popular in center islands and hell strips since it needs little or no supplemental water. Dwarf Leadplant has smaller leaves and makes a slightly smaller plant.
One of the most drought tolerant of all hardy geraniums is Geranium cantebrigiense. It is a cross between G. dalmaticum and G. macrorrhizum, and is a vigorous and spreading groundcover. Its lobed, aromatic leaves turn red in fall and its bright pink flowers bloom abundantly above the foliage for weeks. It is very tolerant of a wide range of soils. ‘Biokovo’ is a blush pink selection that is less vigorous. Both are highly successful in dry shade.
Achillea millefolium ‘Paprika’ is a yarrow with very showy umbrella-like clusters of bright red flowers with yellow centers. The leaves are feathery and attractive and the plant spreads from invasive roots. This aggressiveness can be more pronounced if kept moist, but the plant will rot if kept soggy. If you need to cover a lot of dry ground, this can be a winner; if you have limited space with small or delicate plants, this one can be a weed. Other similar varieties are ‘Cerise Queen’ with cherry red flowers, ‘Heidi’ with bright pink flowers, and ‘White Beauty’ with white flowers. All the yarrows support populations of beneficial insects.
Zauschneria garrettii ‘Orange Carpet’ is a Plant Select winner covered with rich orange, narrow trumpets. It grows 4”-6” high and 15”- 25” wide. It is reported that this variety is less drought tolerant than Zauschneria arizonica. However in our compost-enriched and well-drained xeriscape garden, it is doing well.
Penstemon pinifolius ‘Mersea Yellow’ is a yellow flowered variation of the orange P. pinifolius. It has the same reliable evergreen foliage that looks so fabulous even in the winter, and it blooms profusely and long. The plant gets 12” high and 15” wide and is long lived. It can be used as a single specimen, as an edging, and even as a groundcover. Other summer-blooming penstemons are P. glaber, P. richardsonii, P. mexicali ‘Red Rocks’ and ‘Pikes Peak Purple’ and P. rostriflorus.
Sedum album blooms a refreshing white above its evergreen, nubbly succulent foliage. It is extremely xeric and looks good in the winter as well as at the height of summer. While not a elegant plant, it is very serviceable and good at pioneering rugged and neglected spaces. Most other sedums are summer-blooming as well: Sedum acre, S. hybridum and S. reflexum bloom yellow; Sedum spurium ‘Dragon’s Blood’, ‘Bronze Carpet’ and ‘Elizabeth’ bloom bright pink to near red. Sedums may spread too far, but are easy to remove.
Coreopsis verticillata ‘Zagreb’ has finely dissected foliage and golden yellow flowers. It blooms profusely over a long period and is said to outperform Moonbeam Coreopsis in areas with shorter growing seasons. Other Coreopsis successful in our area are: Coreopsis grandiflora (several selections), C.auriculata ‘Nana’ and C. lanceolata (perhaps the most xeric).
Ceratostigma plumbaginoides, thankfully known as Plumbago, is spectacular in late July, August and September with its striking true blue flowers, and again in the fall when its leaves turn a rich burgundy-red. It is a 6”-10” groundcover that thrives in sun or shade, clay or gravel and needs little water. It is slow to come up in the spring, but is long-lived and very reliable.
These are a few of the water-wise plants that can add color to your garden in the doldrums of summer. Other good choices are: Larkspur, Sempervivums, Sphaeralceas, Acantholimons, Oreganums, Alliums, Lavandulas, Delospermas, Russian Sage, Butterfly Bush, Chocolate Flower; and Scabiosa lucida, Osteosperma “Lavender Mist”, Gazania linearis, Liatris punctata, Scutellaria supina, Monarda fistulosa, Asclepias tuberosa, Papaver croceum, Diascia ‘Coral Canyon, Callirhoe involucrata, Mirabilis multiflora, Blue Elf Delphineum and Nepeta ‘Walker’s Low’.