Severe Drought Reveals Importance of Planting the Right "Native" Plants
by: Forrest S. Smith, South Texas Natives Coordinator(forrest.smith@tamuk.edu)
August 31, 2009, Kingsville, Texas: Conditions of the last year have reiterated the importance of using truly “native” plants in restoration plantings and gardens in south Texas. Droughts, like the current one, clearly demonstrate what restorationists and plant scientists have long harped on when it comes to choosing ecotypic native plant material for a garden or restoration project. Unfortunately, this lesson is being learned the hard way for many, with sickly “native” plants a common sight in some area gardens, and complete death loss of others becoming more and more common. Drought conditions stress plants, and make disease, pest, and poor adaptation issues much more apparent. There are several things to consider when selecting plants for your garden or restoration project.
Not all plants of a given species are appropriate for your planting site. Within a plant species, different ecotypes exist (think races or populations). These different ecotypes have distinct genetic differences, resulting in the expression of traits and growth behaviors that allow them to persist at a location under a specific set of environmental conditions. Tolerance to disease or extreme drought is naturally selected over eons and is genetically programmed into the makeup of a native plant. Soil properties are also an important thing to consider when selecting plants for landscaping. Soil variables such as pH, permeability, and texture all affect a plant’s ability to thrive on a site. Some plant species are well adapted to broad areas and conditions, while others are specialists, adapted to a specific set of conditions. A general rule to follow for the native plant gardener or restorationist is to attempt to use plant material originating from populations native to the same eco-region as the planting site, and in some cases from no more than a hundred miles from it.
An obvious example of different ecotypes of the same plant species can be found in prairie grasses such as big bluestem and yellow Indiangrass. These plants are sold by most native plant nurseries and seed dealers in Texas, but the seed or rootstock of their plants originates from ecotypes from more northern climates. In “good” (wet) years in south Texas these commercially available plants can perform fine in a backyard garden. But exceptionally hot, dry years like 2009 show that the commercially available material of these species is a poor long-term choice for the south Texas gardener. A big problem with these non-locally adapted ecotypes is their attempt to reproduce at the wrong time of the year. They originate from areas with environmental conditions that favor seed production earlier in the growing season. This adaptation results in a flush of growth and seed stalk production during a time when conditions in south Texas are too extreme for the plant to successfully grow in. This attempted growth and energy utilization results in a starved, stressed plant that subsequently dies, or is unable to express its maximum growth potential. Big bluestem and yellow Indiangrass plants grown from seed produced by south Texas populations initiate seed stalk production and rapid growth much later in the fall, a favorable adaptation to avoid our severe summer droughts, and take advantage of fall rains and the later onset of freezing temperatures.
Another lesson learned in native plant gardens this summer is the importance of using the right species of plant for your area. Many folks (including nurserymen unfortunately) think all cenizos are the same, but there are actually several plant species commonly often referred to as cenizo. Two of the common cultivars marketed in south Texas nurseries are Silver Cloud and Green Cloud. While generally similar in appearance, these two plants are completely different in terms of adaptation, origin, and botanical classification. Silver Cloud is a cultivar of violet silverleaf (Leucophyllum candidum), a species found in the Trans-Pecos Region of Texas. Green Cloud is a cultivar of Texas sage (Leucophyllum frutescens) originating from a population in Cameron County of south Texas, and is the species found throughout our region. Recent drought conditions have indicated that Silver Cloud isn’t well adapted to our area, not surprising since the species does not naturally grow in south Texas. Sudden die-offs of these plants have been observed in area gardens this summer. Cotton root rot is the likely culprit. Green Cloud is an ecotypic native to south Texas, and although occasionally affected by cotton root rot, most plants are thriving this summer.
These backyard lessons on native plant selection can easily be extrapolated to landscape scale restoration efforts. The choice of plant species and the source of propagules is one of the most important considerations when attempting restoration, whether the project is in your yard or thousand acre pasture of range land. Through our work, we hope that ecotypic native plants for the large scale restorationists, as well as native plant gardeners in south Texas will become more readily available, resulting in greater success in planting efforts. Let’s hope our learning experiences through the drought of 2009 are almost over, and the rain starts falling again soon!
