Drought and Drought Stress on South Texas Landscape Plants

Drought and Drought Stress on South Texas Landscape Plants
By: David Rodriguez

In nature, water is usually the most limiting factor for plant growth. This is also the case in home or commercial landscapes. If plants do not receive adequate rainfall or irrigation, the resulting drought stress can reduce growth more than all other environmental stresses combined.

Drought can be defined as the absence of rainfall or supplemental irrigation for a period of time sufficient to deplete soil moisture and injure plants. Drought stress results when water loss from the plant exceeds the ability of the plant's roots to absorb water and when the plant's water content is reduced enough to interfere with normal plant processes. In South Texas, plants may frequently encounter drought stress. Rainfall is very seasonal and periodic drought occurs. During drought, local governments may place restrictions on landscape irrigation in order to conserve water, and landscape plants may become subject to drought stress. The use of drought tolerant plants in the landscape can reduce the likelihood of plant injury due to drought stress.

How Does Drought Stress Affect Plants?
A plant responds to a lack of water by halting growth and reducing photosynthesis and other plant processes in order to reduce water use. As water loss progresses, leaves of some species may appear to change color -- usually to blue-green. Foliage begins to wilt and, if the plant is not irrigated, leaves will fall off and the plant will eventually die.

How Long Before Drought Stress Develops?
The time required for drought injury to occur depends on the water-holding capacity of the soil, environmental conditions, stage of plant growth, and plant species. Plants growing in sandy soils with low water-holding capacity are more susceptible to drought stress than plants growing in clay soils. A limited root system will accelerate the rate at which drought stress develops. A root system may be limited by the presence of competing root systems, by site conditions such as compacted soils, or by container size (if growing in a container). A plant with a large mass of leaves in relation to the root system is prone to drought stress because the leaves may lose water faster than the roots can supply it. Newly installed plants and poorly established plants may be especially susceptible to drought stress because of the limited root system or the large mass of stems and leaves in comparison to roots. Always look at a container plants root system before planting. Loosening or cutting the root system at initial planting stage will aide in establishment.

How Does Environment Affect Drought Stress?
Aside from the moisture content of the soil, environmental conditions of high light intensity, high temperature, low relative humidity and high wind speed will significantly increase plant water loss. The prior environment of a plant also can influence the development of drought stress. A plant that has been drought stressed previously and has recovered may become more drought resistant. Also, a plant that was well-watered prior to drought will usually survive drought better than a continuously drought-stressed plant.

What Changes Can Be Made to Reduce Effects of Drought in the Landscape?
The landscape environment can be modified to reduce or prevent drought stress by irrigation, mulching, and providing shade. Reducing the overall water requirements of the landscape is best achieved by initially designing the landscapes for water conservation, including efficient irrigation systems, proper watering and the use of drought tolerant plants where appropriate.

What are the Characteristics of Drought Tolerant Plants?
Some species have an inherent tolerance of drought because they have evolved in arid areas, regions with frequent drought, or regions with soils of low water-holding capacity. Some species have anatomical or physiological characteristics that allow them to withstand drought or to acclimate to drought. All plants have a waxy coating on their leaves called "cuticle," but some species have developed exceptionally thick cuticles that reduce the amount of water lost by evaporation from the leaf surface. Leaf hairs, which reduce air movement at the leaf surface, are another means of reducing evaporation from the leaf. Since the amount of surface area exposed to the atmosphere affects evaporation, leaf size and thickness are other adaptations, with thicker leaves and smaller leaves being more resistant to water loss. Some species have evolved large surface root systems to quickly absorb rainfall, while other species grow deep root systems to tap deep water tables. Some plants avoid drought by dropping their leaves during droughts and quickly regrowing new leaves when environmental conditions improve.

Lists of Drought Tolerant Plants
The plants listed tolerate drought stress better than most landscape plants. Although these plants are considered drought tolerant, new plantings will require regular irrigation for 6 weeks to 6 months or more before they become established well enough to be effectively drought tolerant. Trees larger than two inches caliper will take longer to establish.

Plants are listed by common and scientific names (alphabetized by scientific name) and are divided into categories such as trees, shrubs, groundcovers and vines. Those marked with **** are considered to be Deer Resistant. Also, trees not so marked are vulnerable until they reach a size sufficient to withstand the rubbing of the buck deer.


COMMON NAME/SCIENTIFIC NAME

Drought Tolerant Trees
Cedar Cedrus spp.
Texas Redbud Cercis canadensis 'Texensis'
Citrus Citrus spp.
Loquat Eriobotrya japonica
Yaupon Holly Ilex vomitoria
Crape myrtle Lagerstroemia indica,
Wax myrtle Myrica cerifera
Japanese black pine Pinus thunbergiana
Shumard oak Quercus shumardii
Live oak Quercus virginiana
Mountain Laurel Sophora secundiflora
Bald Cypress Taxodium distichum
Jujube Ziziphus spp.

Drought Tolerant Shrubs

Glossy abelia Abelia x grandiflora
Century plant **** Agave americana
Aloe Aloe
Japanese barberry Berberis thunbergii
Butterfly bush Buddleia spp.
Cactus **** Some Species Cactaceae family
Bottlebrush Callistemon spp.
Dwarf natal plum **** Carissa grandiflora 'Prostrata'
Pampas grass **** Cortaderia selloana
Cotoneaster Cotoneaster spp.
Pineapple guava Feijoa sellowiana
Fig Ficus carica
Kumquat Fortunella japonica
African daisy Gamolepis chrysanthemoides
St. John's-wort Hypericum spp.
Yaupon, yaupon holly **** Ilex vomitoria
Juniper **** Juniperus spp.
Lantana **** Lantana spp.
English lavender Lavandula angustifolia
Texas sage **** Leucophyllum frutescens
Wax myrtle Myrica cerifera
Oleander **** Nerium oleander
Prickly pear **** Opuntia ficus-indica
Pittosporum Pittosporum spp.
Plumbago **** Plumbago auriculata
Pomegranate **** Punica granatum
Pyracantha Pyracantha spp.
Indian hawthorn Raphiolepis spp.
Rose Rosa spp.
Rosemary **** Rosemarinus officinalis
Texas Mountain Laurel **** Sophora spp.
Spiraea Spiraea spp.
Yellowbells, Gold Star Esperanza
Cup of Gold (Cupea de Oro) Tecoma stans
Blueberry, Sparkleberry Vaccinium spp.
Viburnum **** Viburnum spp.
Chaste tree,
'Texas Lilac' Vitex**** Vitex agnus-castus
Yucca **** Yucca spp.

Drought Tolerant Groundcovers
Bermudagrass **** Cynodon dactylon
Daylily Hemerocallis spp.
St. John's-wort Hypericum spp.
Morning glory Ipomoea spp.
Juniper **** Juniperus spp.
Lantana **** Lantana spp.
Liriope Liriope spp.
Rosemary **** Rosemarinus officinalis
Purple heart Setcreasea pallida
Cape honeysuckle Tecomaria capensis
Asiatic jasmine Trachelospermum asiaticum
Society garlic **** Tulbaghia violacea
Zoysiagrass **** Zoysia spp.

Drought Tolerant Vines
Crossvine Bignonia capreolata
Bougainvillea Bougainvillea spp.
Trumpet creeper Campsis spp.
Creeping fig **** Ficus pumila
Carolina yellow jasmine**** Gelsemium sempervirens
Morning Glory Ipomoea spp.
Honeysuckle Lonicera sempervirens
Virginia creeper Parthenocissus quinquefolia
Cape honeysuckle Tecomaria capensis
Confederate jasmine Trachelospermum jasminoides
Grape Vitis spp.


Remember, Learn and Have Fun!

David Rodriguez is the County Extension Agent-Horticulture for Bexar County. He represents Texas Cooperative Extension with the Texas A&M University System For any landscape or gardening information, call the Bexar County Master Gardeners AHotline@ at (210) 467-6575, email questions to mg-bexar@tamu.edu, or visit our County Extension website at http:bexar-tx.tamu.edu

Crepe Myrtle Tips

The crepe myrtles are among the most satisfactory of plants for the South: showy summer flowers, attractive bark, and (in many cases) brilliant fall color make them year-round garden performers. Long, cool autumns yield the best leaf display; sudden frosts following warm, humid fall weather often freeze leaves while they're still green, ruining the show.

Most crepe myrtles in gardens are selections of L. indica or hybrids of that species with L. fauriei. The latter species has attracted much notice for its hardiness and exceptionally showy bark. Queen's crepe myrtle, L. speciosa, grows only in the Tropical South.

All crepe myrtles bloom on new wood and should be pruned in winter or early spring. On large shrubs and trees, remove basal suckers, twiggy growth, crossing branches, and branches growing toward the center of the plant. Also gradually remove side branches up to a height of 4-5 ft.; this exposes the handsome bark of the trunks. During the growing season, clip off spent flowers to promote a second, lighter bloom. Also prune dwarf forms periodically throughout the growing season, removing spent blossoms and thinning out small, twiggy growth.

Crepe myrtles are not usually browsed by deer.

Types of Crepe Myrtle Trees
Japanese Crepe Myrtle. L. fauriei. Native to Japan. Tree to 20-30 ft. tall and wide, with erect habit and outward-arching branches. Light green leaves to 4 in. long and 2 in. wide turn yellow in fall. Especially handsome bark: the smooth gray outer bark flakes away to reveal glossy cinnamon brown bark beneath. Small white flowers are borne in 2- to
4-in.-long clusters in early summer; often blooms again in late summer. Resistant to mildew and best known as a parent of hardy, mildew-resistant hybrids with L. indica, though it is handsome in its own right. 'Fantasy', with even showier bark than the species, has a vase form narrow below, spreading above. 'Kiowa' has outstanding cinnamon-colored bark.

Crepe Myrtle. L. indica. The premier summer-flowering tree of the South. Tolerates heat, humidity, drought; does well in most soils as long as they are well drained. May be frozen to the ground in severe winters in the Upper South, but will resprout. Gardeners there should plant cold-hardy selections such as 'Acoma', 'Centennial Spirit', and 'Hopi'. Variable in size (some forms are dwarf shrubs, others large shrubs or small trees) and habit (spreading or upright). Dark green leaves are 1-2 1/2 in. long and somewhat narrower, usually tinted red when new; they often turn brilliant orange or red in fall. Crinkled, crepe-papery, 1- to 1 1/2-in.-wide flowers in white or shades of pink, red, or purple are carried in dense clusters.

Trained as a tree, it develops an attractive trunk and branch pattern. Smooth gray or light brown bark peels off to reveal smooth, pinkish inner bark; winter trunk and branches seem polished.

Mildew can be a problem. Spray with triforine (Funginex) before plants bloom, or grow mildew-resistant hybrids of L. indica and L. fauriei. Almost all selections with names of Native American tribes, such as 'Hopi', 'Miami', and 'Zuni', are mildew resistant.

Queen's Crepe Myrtle. L. speciosa. Zones TS; 12-9. Tree to 25-30 ft. tall, 15-25 ft. wide. The showiest and most tender of the crepe myrtles, displaying huge clusters of white, pink, lavender, or purple flowers in June and July. Individual blossoms reach 3 in. across. Large leaves (8-12 in. long, 4 in. wide) turn red in fall. Smooth, mottled, exfoliating bark. Rank grower; annual pruning in winter is especially important to control size and form.

Crepe Myrtle Pruning Tips
Don't chop your large crepe myrtles down to ugly stubs each spring just because your neighbors do. This ruins the natural form and encourages the growth of spindly, whiplike branches that are too weak to hold up the flowers. To reduce a crepe myrtle's height, use hand pruners or loppers to shorten the topmost branches by 2-3 ft. in late winter, always cutting back to a side branch or bud. For branches more than 2 in. thick, always cut back to the crotch or trunk. Don't leave big, ugly stubs.

Thanks to Houston Plants & Garden World for the info! www.houstonplantsandgardenworld.com

Butterfly Garden Pathway Bricks have been installed!

Our Community Butterfly garden is looking awesome with the addition of the new pathway bricks! The bricks were recently installed, and set in concrete to ensure their placement. If you purchased a brick, (THANK YOU!!), go by the garden and see your brick! If you were unable to order this time, go check out the garden and see what the bricks look like -- start thinking of what you want your legacy to be. The Garden Club will begin taking orders again in the Fall. Watch the blog and community website for information.

Yard Tour

The CCLGC 2nd Yard Tour was held on May 21st. The tour started at the community butterfly garden and moved thru the yards of Sandra and Kenneth Gilbert and Marcia and Dave Mausolf. Lunch was at Black Horse Country Club. Thanks to Cathy Oland for once again organizing this event, and thanks to those who allowed us to visit their yards!

May 2011 Yard of the Month

Congratulations to Chris and Toni Yargo - our May 2011 Yard of the Month winners! They live at 12111 Cypress Creek Lakes Dr. You have a wonderful yard -- thanks for your hard work!

May 2011 Meeting

The final meeting of the 2010-2011 Garden Club years was held on May 9th. Bonnie and Richard Segura were very gracious in allowing an impromptu tour of their beautiful rose gardens before our meeting began. Thank you so much!!



This meeting was "bitter sweet" for Debbie and I. We are turning over the lead of the club to our newly elected President Sandra Gilbert and Secretary/Treasurer Marcia Mausolf. Debbie and I have had a wonderful two years, have enjoyed watching the club grow, and making many new friends along the way. We are looking forward to the new direction that Sandra and Marcia will lead us in.

Sandra gave us an outlook for the next 2 years, and introduced a few of the leads for our committees:
Programs: Kathy Booth
Yard of the Month: Mike Owens and Bonnie Segura
Tours: Cathy Oland
Social Media: Patti Foucha

Final Meeting of the 2010-2011 Garden Club Year

Our final meeting of the 2010-2011 Garden Club year will be this Monday, May 9th. At this meeting we will review our final projects for the year and install our new officers for the term of 2011-2013. The meeting will be held at 26310 Ridgefield Park Ln, We look forward to seeing you there!