PLANTS OF ORNAMENTAL VALUE FOR THE RIO GRANDE VALLEY OF TEXAS
W. H. FRIEND
Former Superintendent, Texas Agricultural Experiment Substation No. 15, Weslaco
This publication presents a summarization of the accumulated experience of the Experiment Station Staff and certain cooperators with the ornamental material presented. All plants have been listed by both their common and scientific names in the hope of making the publication of widest use. A short discussion of the more practical phases of growing and protecting ornamental plants has been included for the convenience of home gardeners. The discussions relate only to plant material considered to be useful in the Lower Rio Grande Valley, but all material tested has been listed in tabular form and arranged according to scientific name.
Related Texas Station publications include Bulletin 447, "Trees and Shrubs of Northwest Texas," Bulletin 551, "Valuable Plants Native to Texas," Circular 87, "Rose Diseases" and Circular 90, "Rose Growing for the Home Gardener." The last three, especially, will be found useful to the home gardener in the Lower Rio Grande Valley.
Many thousands of dollars have been wasted in the Lower Rio Grande Valley in an effort to establish plants in this environment that are not adapted to prevailing conditions. Many plants which are not adapted to our soil and climate should give way to more suitable material. For example, the very attractive subtropical species of Casuarina are to be preferred to the Arborvitae, and we should learn to avoid the pest-ridden Hackberry when it is just as easy to grow the beautiful Silk Oak or the Brazilian Pepper Tree. Visiting horticulturists have lamented the use, by amateur gardeners and even by municipalities, of the less attractive deciduous plants when they might have used evergreen species that lend beauty to the landscape throughout the entire year. Why grow Chinaberry trees, Spiraea and Honeysuckle in a land that will produce the lordly palm, beautiful Orchid Tree or the showy Flame Vine?
The Lower Rio Grande Valley is a region of fertile soils and fairly equitable climate, but it should be freely admitted that conditions are not favorable for the growing of many types of plants. It has been said that it is much easier to acclimate a tropical or subtropical subject to the temperate region than to grow plants from northern latitudes in the near tropics. Gardeners who have attempted to establish Dogwood or Maple trees in this region can testify as to the difficulty of using northern materials. Climate may not always be the most important factor affecting adaptability of many plants, as soil and irrigation also handicap the chances of certain exotics.
It is obvious that the appearance of many premises could be greatly improved by the judicious use of a few inexpensive ornamental plants. This aesthetic value is entirely aside from the practical benefits to be derived from a few well placed shade trees, a windbreak planting or a protective hedge of thorny but attractive native shrubs.
When fitting plants into the landscape scheme, it is well to consider that some plants have certain requirements that must be supplied from the environment, while other plants can endure and thrive in positions that would prove fatal to other subjects. By having a working knowledge of available ornamental material it is possible to fit the subject into the environment rather than attempt the costly business of modifying the environment. It is a known fact that some types of plants thrive in shady locations while others must have full sun. Likewise, some plants will endure drought and can be planted in locations where they are likely to be neglected while others must be supplied with an abundance of soil moisture. Plants such as Sea Grape and Australian Pine will thrive in brackish soil, while salt-sensitive plants such as the Loquat and Avocado must be planted only on the best drained soil.
Resistance to cold or the ability to survive expected minimum temperatures is not prerequisite to adaptability as may tender plants such as hibiscus, poinsettia and bauhinia are frequently killed to the ground, but their perennial roots survive and the plant soon attains its original size.
Certain plants do not thrive in the slightly saline, alkaline soils of this region because of deficiency diseases brought about by the high lime content of many Valley soils. Roses are not well adapted to Valley soils, but thousands of healthy, prolific plants are grown in this region, simply by modifying the soil to correct the alkalinity.
Immunity to certain soil borne diseases like root rot and root knot, while highly desirable, is not absolutely essential. It is now known that susceptible plants can be grown on soil that is subject to infection from these two diseases. By planting in sod and through soil sterilization by disease inhibiting chemicals it is possible to grow successfully a wide variety of ornamental plants which are highly susceptible to these soil diseases.
METHODS
The information presented in this publication has, for the most part, been obtained from adaptability tests conducted at the Lower Rio Grande Valley Experiment Station. In cases where no specimens were grown under actual test, and where the data pertaining to plant characteristics and adaptability are based on material grown away from the station, an asterisk (*) has been used to identify this material. Most measurements and observations were based on the performance of plants ranging in age from five to fifteen years. In many cases, plants have been eliminated from the tests after a single year where they have been found to be totally unadapted. Since station experience has been compared with that obtained from larger scale trials by local nurserymen and home gardeners, it is believed that the adaptability ratings are reliable.
In arriving at an adaptability score for any plant, the ability of the plant to become established when given reasonably good care, and the rate of growth and general vigor of the subjects throughout the test, were given due consideration. A score of zero (0) indicates that the subject can be established only with great difficulty (including special care) and that the few specimens which do become established are weak and obviously unadapted to their environment. A score of 10 indicates that the subject is well adapted.
The number of plants used in arriving at the figures presented in the tables ranged from two to 25, or more. Actual measurements were not taken on more than five specimen plants thought to be typical of the variety.
Yearly records of performance were kept, and adaptability ratings, with comments, have been noted in each annual report of the station. The data herein presented represents the period of years summary of these reports. This applies both to the material grown on the farm and to that grown by cooperators.
Material used in these tests were secured in large part from commercial nurseries in California and Florida. Large quantities of new and untried plants were secured through the Office of Plant Exploration and Introduction of the United States Department of Agriculture. Native plants were grown either from seed or from seedlings brought in from the brush country.
Some of the plants used in these studies were grown in locations where they would ordinarily be used in the landscape scheme, but most of the plants were grown in a plant introduction garden where they could be regularly cultivated, irrigated, and cared for like ordinary row crops. No special soil treatments and no regular spray program was used in growing any of the plants, except subjects known to require special soil adjustment for their normal growth.
Ornamentals for the Rio Grande Valley