Primetime Newspapers
By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist
Week of March 13, 2006
 “To Water or Not To Water”  

            There is an interesting debate going on among horticulturists.  The basic question is whether it is more important to water our plants because of the drought or is it more important to reduce water use on landscapes in order to reduce the drop in the aquifer that will eventually lead to drought restrictions.  It is hard sometimes to have a rational discussion on the issue because some of the voices are a bit strident.  I think the best way to proceed is with moderation.  Irrigate enough to protect your plants, but do not waste water and end up contributing to a quicker entry into drought restrictions. 

 

            The drought over the last ten months has been significant, but not as devastating to our landscapes as some sources contend.

 

·      We only had about 16 inches of rain in 2005, half our average of the last ten years, but we had four wet years before it.  The trees and shrubs that are well adapted or native to the area are capable of surviving long periods of drought. 

 

·      Further, last year (2005) was relatively cool and the rains we had were well timed.  Per capita water use was only 130 gallons/person/day because of the cool weather and rains in July and other key times over the summer.

 

·      There are some obvious results of the drought, evergreen plants such as ligustrum, primrose jasmine, Asiatic jasmine, and even oleander are showing leaf drop and burn, but there is no real evidence of tree, shrub or lawn kill.  Anecdotal evidence cited by some sources is a weak replacement for any real measurement of plant die-off.  Every month some plants die in the San Antonio area whether we have a drought or soggy period.  Most, however, can tolerate more severe drought periods than we have experienced.

 

·      Some sources have stated that the dormancy of our lawns is due to drought rather than cold.  We have had five freezes in many neighborhoods, which is certainly enough to make our hot weather grasses go dormant, but I am not sure it matters.  In the case of Bermuda grass, buffalo, and zoysia, dormancy due to cold and dry weather is basically the same.  The grasses emerge from both when the combination of warm weather and moisture is adequate. 

·      St. Augustine is a different story.  It has limited capability to go dormant from either stress.  The argument is that if the dormancy we see in our St. Augustine lawns is drought induced, it portends terrible damage as we move into warm weather.  It is true that to keep St. Augustine healthy through the winter, it does require a watering every three – four weeks.  It is a problem, however, if we go overboard and begin watering every week too early in the year. 

 

·      The normal pattern of heavy watering of lawns usually begins inlate June or early July.  That increase in landscape water use coincides with the decrease of water use by agricultural producers.  The corn crop irrigation ends by July 4.  If San Antonians irrigate our lawns at the same time as the farmers irrigate their corn, the aquifer will drop quickly to levels that require drought restrictions.

 

My recommendation is that we stay very conservative about our landscape watering so we can postpone drought restrictions.  Your St. Augustine lawn and newly planted trees or shrubs only need water every three – four weeks until June, unless we have exceptionally hot weather. 

Established, well adapted trees and shrubs can survive long periods of drought without supplemental irrigation.  When you do water, use drip irrigation and handheld hoses and other efficient methods when possible.  The plants will survive fine and we will postpone drought restrictions.