What does xerophytic mean anyway? Its root word, xeros, is the Greek word for “dry.” Botanists have long used this term to denote plants that use little or no water but you are probably more familiar with a similar word of more recent coinage, xeriscape. This concept of landscaping with xerophytes has gained popularity in Texas and throughout the West as a logical response to the threatened depletion of aquifers, high water costs, salty well water, cranky pumps and/or the desire to stay in the shade through August. Yet for all its simplicity, there is more to xeriscape gardening than planting from the recommended list in your native plant book and then throwing away the water hose. Why some of these plants make it while others do not is the subject addressed in this article.
When you buy a 4-inch nursery pot of drought-tolerant, golden-flowered calylophus you cannot just tuck it into the edge of your rock walkway, brush the dirt off your hands and leave on vacation… especially if its summer vacation! In nature, the roots of this plant can grow to a depth of 5 feet in search of moisture but your plant’s little 3-inch root system is going to need some water to get established. If you plant in the cooler weather of fall, this hardy evergreen bloomer will begin to establish its roots with winter moisture so that by its first summer it should be able to survive with only a few well-timed artificial cloudbursts each month.
The size of the root system and the time of the year in which you plant – that is, rainy season as opposed to dry season, cool temperatures versus heat have a lot to do with whether your drought-tolerant plants will need supplemental water. The texture of your soil (and sometimes its acidity or alkalinity) is a big factor in determining your xerophyte’s life span. And finally, individual flowers, shrubs and trees vary in their specific water requirements. The ubiquitous yaupon holly, like most native trees, can take periods of flood and periods of drought, once established.
Gardeners have found that many smaller xeric plants like butterfly bush, mealy blue sage and gaura, when put into traditional flower beds alongside daylilies and roses, seem to outdo themselves in compost and water. But, should the overconfident experimenter try adding purple-flowering culinary sage, cheerful blackfoot daisies, or Silver Mound artemisia to the combination, he or she will get their first lesson in real life xeric gardening.
The xeriscape “failure stories” that I hear most often fall into two categories: “I never watered it but it died” and “I watered it but it died.” Wading into these contradictory statements is a little like untangling a mess of barbed wire: there are a lot of catches and it takes some time.
All plants need moisture. The first thing a windblown, tumbled, scarified or excreted little seed requires is water to soften its outer coating so it can put forth a tiny hair-like root. If you have ever planted native seeds in a seed pan, I am sure you have been struck by the length of the tenacious root compared to the tiny green sprout which shows above the potting soil. In nature, natives survive drought by developing root systems that find water, but as tiny seedlings destined for your flower bed, they need some gardener-supplied moisture to develop those roots.
When you scatter California poppy, scarlet flax, or Drummond phlox late in the fall, you will get a better return from your seed if you imitate nature’s optimum conditions – thoroughly moistening the planting area and then sprinkling it lightly when the seedlings appear. Later, if the weather has not cooled down, water as needed. Once you get a good stand of wildflowers reseeding each year, you will not have to water because each plant puts out so many seeds that some portion will sprout and bloom. However, if you really depend on a spring showing of annuals in a prominent bed, watch out for warm, dry Decembers and perhaps water some to ensure a good germination of your seed.
In most parts of Texas our moisture comes in the winter. Many of our native plants, like the natives of the regions surrounding the Mediterranean, are suited to cool, wet winters and long, dry summers. Mediterranean herbs such as rosemary, thyme, oregano, curry plant, santolina, germander and sage are some of our best xeric plants. Greek oregano can take some summer watering and makes a nice evergreen border for any garden situation but the others will not appreciate a regularly watered bed.
These evergreen herbs and cool season bloomers like violets often have a summer dormancy period in which they, in effect, “hole up,” conserving their energy until the heat begins to ease and moisture returns. This is why an August “norther” combined with a good rain will momentarily fool an oxeye daisy for an out-of-season bloom or two. The fall-blooming aster stays on hold through the heat, having a slightly waxy leaf like the desert shrub, creosote bush; then, with cooler weather and the first hint of rain, becomes a solid mass of lavender blooms. All of these plants can survive without additional watering but they will bloom more and look better with a simulated summer shower now and then.
BULBS & RHIZOMES
Old fashioned “cemetery iris” (Iris alba) and spuria iris are not usually thought of as xerophytic plants but anyone who drives the back roads of Central Texas knows that nobody waters these bar-ditch irises. Plants which grow from bulbs, corms, tubers and rhizomes (as in rain lilies, liatris, fringed-leaf pacoon, and iris) handle drought in their own unique ways. What is more refreshing during the summer heat than a good rain followed by a yard full of fragrant rain lilies? Within a few days the white or yellow flowers put out their seed and die back, then the little bulb begins again to store its energy up for the next cloud burst. Liatris waits for the first break in the August weather – there is always a day, you can feel it even though the temperature is in the 90s, when there is a fall-like quality in the air – to send up its magenta flower stalk in the dry pastures. Coral colored spider lilies and deep red oxblood lilies hold off for still cooler weather and a little bit of fall moisture before blooming and then retreat to their snug storehouses beneath the ground until next year. All these plants need water to bloom and their moisture requirements are suited to our winter rainfall patterns… but be careful about watering bulb beds during the summer when hot, wet soil can cause rotting.
Next to judicious supplemental watering, soil texture plays a major part in the success of a low maintenance xeriscape. Many hardy drought-tolerant plants can adapt to sharing a bed with water lovers if your soil is well drained, which can be defined as anything from loam to gravel to sand that is deep enough that your xeric plant’s roots never have to stand in water. The “I watered it but it died,” failure stories usually come from people who have heavy clay soil, a difficult situation for Salvia greggii, damianita, cenizo, madrone, blackfoot daisies, yuccas, cactus, agaves, red-hot poker (Kniphofia), lamb’s ears, Jerusalem sage, wooley stemoidia and lavender to name a few. By raising your beds and creating a looser soil, as Stephen F. Austin University has done in their West Texas (in East Texas!) Garden, you can incorporate xerophytes into your landscape even in parts of the state with higher annual rainfall.
Clay soil is not necessarily the death knell of all xerophyic plants. Where moisture is seasonal (winter), Maximilian sunflower, rudbeckias, liatris, prairie phlox, meadow rue, Lindheimer’s muhley grass, inland sea oats, milkweeds, wax myrtle, nandina, Cassia corymbosa and goldenrod do not even seem to notice the foot-deep cracks in the summer clay nor the gumbo of winter. In fact, unwary gardeners who plant Maximilian sunflowers or liatris in their deep beds will be disappointed with the gangly, over-large results of these plants outside of their natural habitat.
A LITTLE STRESS
The last “catch in the tangle” is hinted at in this Maximilian sunflower/liatris syndrome. In addition to being able to survive with less water, xeric plants usually do not need the rich organic matter of traditional flower beds. A little stress brings out the best in them, keeping them compact and ready to bloom.
As a xeric gardener, you can take care in preparing your soil, end a drought if need be, and settle territorial disputes once in a while, but the real joy of xeriscaping is sitting back and discovering through the seasons the little everyday surprises and beauty of plants as they were meant to be.