Weekly Express-News Article

By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist
Saturday, March 8, 2008
 “Lawn Grass Care”

            It is too early to fertilize the lawn but there are plenty of other important tasks to do. 

            Wait until after April 15 to fertilize the lawn or until you have mowed real grass two times.  St. Augustine, Bermuda, zoysia, and buffalo grass are warm weather grasses.  They do not grow well or pick up nutrients efficiently until the soil and air temperatures are warm. 

            The winter weeds such as rescue grass, bed straw, wild carrot, annual bluegrass, dandelions, thistle, and henbit are working hard to set seed.  The seed, if it matures, will provide next winter’s generation of weeds.  To reduce the amount of seed available, keep the weeds under control by mowing.  In the shrub border, hand-pull the weeds or run through with your string mower to keep the seed head from maturing.  For most winter weeds it is too late to control them with contact herbicides.  They produce their seed and decline as the temperatures warm anyway. 

            The warm season weeds begin to germinate in March and April if the temperatures are mild.  There is still time to apply a pre-emergent herbicide to control most summer weeds, especially crabgrass and sand burs.  There are a number of herbicides that work for the job; Amaze and XL seem to be effective.  If your summer weeds are mostly broadleaf weeds, Portrait is one of many choices.  Check out the label of the available products. 

There are several keys to effective pre-emergent herbicide use.  Timing is number one.  Apply the material before the target weed has germinated.  It is too late if the weed is already growing.  Selecting the right herbicide for the offending weeds is also important.  The good news is that your choice usually only involves determining whether the weed is a grass or a broadleaf.  Another factor is to follow the label instructions closely.  Pre-emergent herbicides act in several ways, but most seem to provide a barrier in a shallow layer of soil on the surface of the lawn.  Apply an incomplete layer of herbicide or disrupt that layer by aeration or excessive traffic and the weed prevention will be ineffective.

Sand burs are especially difficult to control.  The pre-emergent herbicide has to be applied twice per season (March 1^st and May 30^th) over two years to expect effective control.  Refer to www.plantanswers.com for more detail about sand bur control, including interim practices to kill the plant that escape the first year of pre-emergent control. 

Do not aerate and top dress after you apply a pre-emergent herbicide, but otherwise it is not too late to rent an aerator and do the job.  Aeration and top dressing contributes greatly to a healthy attractive lawn. 

Irrigation is an important part of lawn care in our area.  The trick is to apply enough water to keep the lawn healthy without wasting any water.  The easiest way to do that is to follow the watering advice provided each week under the SIP Report in the San Antonio Express-New.  You can also receive a personalized e-mail recommendation if you visit the SAWS website at www.saws.org and click to water conservation.  SIP was developed by SAWS and the AgriLife Extension Service through four years of experimentation relating water needs to weather conditions.  Each year for the last ten years, about 5,000 area residents have taken advantage of the personalized SIP communication.

If you prefer not to enroll in SIP or use the published SIP recommendation, plan on watering your St. Augustine lawn every three weeks in the winter if it does not rain and every week once the lawn begins growing.  You have more flexibility with Bermuda, buffalo, and zoysia grass because they go dormant in the winter time and do not necessarily have to be watered.  In the summertime, zoysia takes as much water as St. Augustine to stay green and buffalo and Bermuda grass require a little less.  For detailed discussions on lawn water needs, visit the SAWS website and/or www.plantanswers.com.