A Xeriscape Harvest

For most people, harvest time brings to mind a cornucopia of veggies and fruits. For me, the end of this 2009 growing season has been a fruition of over 20 years of cultivating a xeriscape where most of the trees and shrubs have been watered 5 times a year or less. These self-imposed watering restrictions have demonstrated which plants can survive and thrive under serious water shortages. I have done this both to encourage water conservation in Colorado and to demonstrate that a dry western landscape can be beautiful.

         The reason why 2009 feels like a harvest year is because many of my woody plants are now mature and because with all the rain we’ve been getting, my xeriscape has never looked better at the end of summer.

So I would like to brag about not only my personal success but about the success of some really great Colorado-adapted woody plants.

         Because most of these photos were not taken in flowering season, they are not about color. They are about enduring structure in a landscape, health and attractive vitality, diversity and a Colorado style. In some cases, these plants have more than a description; they have a story too. Here are a few of the best.

         Golden Rain Tree, Koelreuteria paniculata, came to me as a seedling from another gardener and, in fact, I would consider this seeding habit to be one of the few disadvantages of this 20’-35’ flowering tree. Its panicles of golden yellow flowers decorate the tree in July when they are most welcome in a xeriscape, and the pods that follow turn reddish, then tan and are shaped like little Chinese lanterns. The other major disadvantage is the tendency for the tree to make weak branching that can split. My tree was weak from the beginning, but proves that proper pruning can prevent damage. Golden Rain Tree is very heat and drought tolerant.

         Dwarf Blue Rabbitbrush, Chrysothamnus nauseosus nauseosus, seeded itself into my yard from native ones in the neighborhood. The photo is of two plants that I let grow together and which have thrived with no irrigation for the last 15 years. Usually it grows to 2’x2’ or 2’x3’, blooming from late summer into fall a cheerful yellow, which is welcome at the end of the season. It is easier to use in an urban landscape than the big rabbitbrush, because it is tidy and with one shearing a year after bloom, even elegant. The bluish foliage contrast nicely with the greens of other plants.

         Cercocarpus ledifolius, the Curlleaf Mt. Mahogany, is one of my favorite plants. It is a large shrub that grows to 12’-18’ high and 8’ wide, and is generally slow-growing the first 4 or 5 years and then grows moderately fast even with 5 waterings a year. My 23 year old specimen has been through drought, heat, wind, heavy wet snow and it’s evergreen beauty remains unscathed. I sheared it gently for the first 10 years to keep the long growth more compact, then did little or no pruning for the last 13 years. Although the flowers are inconspicuous, the feathery seeds can be showy and the light grey bark with the dark green foliage are beautiful 12 months of the year.

         One of our gardens is an unwatered “native shrub bed” where the  only non-native woody plant is Russian Hawthorn, Crataegus ambigua. It performs like a native, yet is not invasive and the birds love it. The tendency to horizontal branching can make it broader than tall, 15’ tall and 20’ wide at maturity; and it lends itself to a macro-bonsai or character-tree style. In spring the white blossoms can cover the tree and the ½” cherry.red fruits are abundant and very showy. Two other hawthorns, Washington Hawthorn and Toba Hawthorn, have also performed well for me in my dry landscape.

         I have the native Chokecherry, Prunus virginiana melanocarpa, growing in the hot southwest corner of our north Boulder property, in the “Wildlife Garden”. It can grow 10’-20’ tall and individually 8’-10’ wide, but it suckers a lot so it can make colonies. It is usually said to require moderate water, but mine has not had that luxury. For the last 20 years my Chokecherry has provided me with flowers, the birds with fruit and butterfly larvae with leaves, with only 4 or 5 waterings since it was established. For that, I have been willing to put up with a little wilting, a few unwanted seedlings and a little removal of dead wood due to drought.

         Mahonia aquifolium, Oregon Grape Holly, was for me an example of folly leading to insight. I planted it in full sun, because I didn’t know it was supposed to be a shade shrub that needs moderate water. Now 15 years later, it is 5’ high by 10’ wide and thriving even though it was almost never watered after it was established. This is astonishing since it is a broad-leafed evergreen, native to the coastal mountains of Oregon. It bears fragrant yellow flowers in spring and blue berries in summer. It does resemble our native Mahonia repens which stays a groundcover. In winter, the glossy, holly-like evergreen foliage turns purplish. Winter sun, drought and sub-zero weather can cause some leaves to burn, or rarely, to fall off; but it always recovers quickly with fresh leaves covering up the damage the following spring.

         I like saying that plants are like people: we have our pluses and our minuses. The Desert Mahonia, Mahonia fremontii, was only 6” tall, when it came to me 18 years ago from a local grower of native plants. Now it is 8’ tall and 6’ wide. This evergreen shrub has small blue, holly-like leaves that are reddish as they emerge. In spring the yellow, honey-scented blooms that perfume the whole garden, and following the flowers in late summer are dark red fruits that are quite tasty. The “minus” is its habit of dropping 10%-20% of its leaves in the fall which, when dry, can pierce the skin or at least make weeding around it a real pain. Do not follow my example and plant Desert Mahonia amongst perennials; put it instead in a shrub area where it can be mulched. Now I have to use a shop vac to remove the dead, spiny leaves. Although it is quite drought tolerant, I think the leaves look better in winter if it is planted where it is protected from winter sun. All things considered, it is one of my favorite companions.

         I mail-ordered the White Tartarian Mulberry, Morus alba tatarica, in my salad days, when I was green and inexperienced. I planted it without proper preparation, forgot to water it too many times, and it is now 25’ tall and doing fine. It is one zone hardier than either the red or black mulberry and produces white fruits that don’t stain the surrounding are and are supposed to fool the birds so we humans get some to eat, but it doesn’t and we don’t. Birds adore mulberries. The red mulberries that are more common in Colorado are usually prone to twig die-back in the winter, which requires meticulous pruning to look good, but this variety is hardier and does not have that problem. It did take about 15 years to make a decent tree, under very low water conditions, but it has made a fine screen. And even though I don’t get fruit, I have been visited by the colorful Bullock’s Orioles.

         Sweet Mockorange, Philadelphus coronarius, is not offered by any of the local wholesale nurseries that I know of, and Michael Dirr in his classic Manual of Woody Landscape Plants says of this entire genus: “…vigorous, easy to grow plants…in flower they are attractive to some, but the rest of the year (about 50 weeks) are real eyesores.” Of course, Mr. Dirr is not from dry Colorado where any flower that can perfume the air is a treasure.

         I found one in bloom in Boulder by following the sweet fragrance for about 80 feet. It was growing next to an alley, 10’ high and perfuming the entire neighborhood. So I begged cuttings and when it was big enough, planted it with another thug, the gallica rose ‘Complicata’. The rose keeps the bare legs of the Sweet Mockorange covered and the two of them often bloom together, creating a magnificent effect of bloom and intoxicating fragrance, for perhaps only 2-3 weeks a year. It thrives on the west side of my house where the late afternoon sun bakes it and the winter wind sandblasts the paint off the walls behind it. I do water it 5 or 6 times a year and give it a little rose feed and genuine love. And continuing the gardening tradition, I share it with other admirers.

         Perhaps the photos with this article do not have the color necessary to find their way into Fine Gardening Magazine, but they represent a real harvest in the cultivation of Colorado Sustainability. They demonstrate not only drought tolerance, but the capacity to endure years of heat, wind, extreme temperature changes, lean soil with tough-love care and no chemical fertilizers or pesticides. They radiate a vitality that shows that they actually like living in Colorado. And you are welcome to come out to visit them and our other thrivers and survivers at Harlequin’s Gardens nursery, during open hours. Our display gardens are the fruits of our testing plants for their capacity to adapt to Colorado conditions with little fussing and it is our pleasure to share them with our community and fellow-gardeners.