Plant Answers

PRIMETIME NEWSPAPERS WEEKLY COLUMN
Week of March 25 2002

By Calvin Finch, Conservation Division, Manager, Water Resources & Conservation Dept., SAWS, and Horticulturist

THOU SHALT NOT…

This is a “thou shalt not…” article. Thou shalt not apply fertilizer too early, use “weed and feed”, or water inappropriately. Resist the temptation to fertilize the lawn too early. Fertilizer applied before the roots of your St. Augustine grass are active results in wasted nitrogen. The best way to determine if the roots are active is to note the number of times you have mowed real grass, not weeds. The second mowing marks the point when the roots are active. In San Antonio that time is usually around May 1. That’s right, the most efficient time to fertilize our lawns is about May 1.

“Weed and feed” products are not appropriate for the South. The best time to apply herbicides is not the best time to apply fertilizer. You are wasting one or the other of the ingredients. The other thing that happens with “weed and feed” is that we forget that there is herbicide in the fertilizer and it gets applied to the garden or flowers accidentally. This accident is especially likely if part of the bag is stored.

After we have experienced about three weeks of warm weather, the lawn is ready to green-up. Most years the necessary water for green-up is provided by rains. Irrigation only needs to be used in the spring about every two weeks if we do not receive rain. Apply about one-half inch of water with each irrigation. To calculate how much time it takes to apply one-half inch of irrigation, lay out three or four pie plates or other shallow vessels at various places in the yard. Next, run the irrigation for 15 minutes and then use a ruler to measure how much water is in each pan. You will then need to average the amount of water per pan and then calculate what part of one-half inch it is. For many systems about .25-inch of water will be applied in 15 minutes; so, to apply .5-inch the sprinkler should be operated about one-half hour.

Another good way to determine how much water your lawn needs is to follow ET recommendations. ET is a measure of the actual water used by the grass in the last week. Listen to my radio show on KLUP 930AM at noon on Saturdays or 1:00 p.m. on Sundays for the recommended applications. You can also call the ET hotline at 281-1478 for the same recommendation. The rate is the same for zoysia and St. Augustine in the sun, but less for Bermuda grass in the sun or zoysia and St. Augustine in the shade. Buffalo grass in the sun requires the least irrigation of all, about one-half the water required for St. Augustine grass. Homeowners with a control box could set a schedule at .25 inch, one at .5 inch, and one at .75 inch. Based on the ET recommendation, you can pick the right schedule each week or two.

Remember that if you water your lawn with a sprinkler, the law requires that you do so between 8 p.m. and 10 a.m. only. It is also against the law to waste water. One of the definitions of water waste is to have water leave your lawn to run down the street or into the storm drain. Water wasters can be reported to SAWS by calling 227-6143, but the best thing to do is just remind your neighbor what the rules are. If everybody uses water efficiently there will be plenty of water for all of our needs.