Plant Answers

Weekly Express-News Article
By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist
Saturday, July 14, 2007

“Excess Rain Strategies”

It is hard to remember that one year ago we were in the midst of a two year old drought. Half way through 2007 we have nearly as much rain as our yearly average. The excess moisture is reflected in rain forest like growth of our landscapes and problems due to soggy soil.

The trick to lawn care in such weather is to find an opportunity to mow the grass. Ideally the lawn should be dry when you mow. In conditions like we have faced in the last four weeks it is advisable to use every period when the grass is relatively free of water on the blades, to rev up the mower, and cut a portion of the lawn.

If you have been on vacation and return to find your lawn 8 inches tall and loaded with weeds it can appear that you never will regain control. Take heart, the rains will end; they always do in San Antonio. Here are some tactics to consider to win back your lawn. Do not attempt to cut all the excess grass with one pass through. Mowing off six inches of grass at one time is not good for the mower or your lawn. The lawn mower will stall and the cut off blades will bury the growing points of the grass plants under a layer of hay.

Mulching mowers are especially prone to stall in deep grass. Set the mower at its highest setting and mow the lawn at that level before lowering the blades to the recommended height for the grass variety and mowing a second time to bring the lawn to its normal cutting height. (St. Augustine, 3 inches; zoysia, 2 inches; Bermuda, 1.5inches; buffalo, 5 inches). The grass clippings will be 2-3 inches long instead of 6 inch pieces. The smaller cuttings decompose more quickly than the larger pieces.

We normally do not rake our lawns after mowing, because the cut material decomposes quickly in our climate and recycles nutrients back to the lawn. With current conditions however, a light raking to remove excessive lawn clippings may be desirable. Add the clippings to the compost pile or spread them in the shrub border.

In addition to tall grass, the heavy rains have stimulated and supported an exceptionally heavy growth of weeds. It is always best if the weeds can be pulled by hand to insure that the roots are included, but in the interest of getting control of weeds in shrub borders and fence lines, it is acceptable to cut off the tops with your string mower. Be careful not to girdle shrubs or trees in the process.

Periods of continuous rains make it hard for us to keep up with lawn growth and to control weeds, and root damage can also occur. Roots of susceptible plants can drown in poorly drained soils if the soils stay soggy over a period of days. The root damage translates to leaf yellowing, leaf drop and even plant death. The damage can be visible during the wet period or only show up when the rains end and hot dry weather returns.

There are a few things to do to reduce damage and encourage recovery.

• Enlarge drainage holes on containers where the water is not flowing through the pot.

• Containers can be temporarily turned on their side to encourage drainage and reduce entry of more moisture into the pot during rainy periods.

• The root balls of newly planted trees and shrubs can be temporarily removed from their planting holes to allow them to dry out. If the planting area has a long term drainage problem move the plant to a better drained location.

• Do not add fertilizer to plants with root drainage and showing the excess water symptoms. The fertilizers are salts that add to the damage.

• Repot container plants in a larger container with quality potting soil if the poor drainage is due to the plant being root bound. The root ball can even be trimmed with a butcher knife to make room for new potting mix.

• Remove the mulch from around plants showing the symptom. Mulch is essential to keep the soil cool and reduce evaporation in time of dry weather, but can slow drying of soils during periods of continuous rain.