EFFICIENT IRRIGATION OF TURF

In semi-arid and arid regions, residential lawns should be limited to small areas that provide functional or recreational benefits. Grass is best watered with an automatic sprinkler system adjusted to the seasonal requirements of the turf, and targeted only at the grassy area. However, be aware that even the best sprinkler systems are highly inefficient. Many respected system designers acknowledge that the highest achievable irrigation application rate efficiency for such systems is 60%, i.e., 4 of every 10 drops do not do make it to the root zone.

Determine the output of your sprinklers
Factors such as the number and type of sprinkler heads in your system, their spacing, and water pressure affect the amount of water the system distributes. To test your own system, set out six or more straight-sided cans of the same type between the sprinkler heads. Run the sprinklers for a 20-minute period during the time you normally irrigate, then measure with a ruler the amount of water collected, determine the average amount, and multiply by three to calculate the amount applied in an hour. (Significant variations in the collected amounts will indicate spacing/coverage or blockage problems).

Check with your local Cooperative Extension Office for the monthly recommended amounts for your particular grass type and adjust your watering accordingly. The root zone will generally be replenished by the application of ½ to ¾ of an inch of water.

How much to water
The answer depends on the type of grass, the evapotranspiration rate of the area at the time of watering, the season, and soil type. One way to determine the appropriate amount to water is by checking soil moisture an hour after watering. Insert a long-bladed screwdriver or similar tool into the soil; the depth of water penetration will correspond to the depth the blade can easily reach. Ideally, you should irrigate deeply, and as infrequently as possible, depending on your grass type. A soil moisture depth of 6 inches is recommended for Bermuda grass. Too shallow watering will only wet the top layer of soil and grass roots will not grow deep enough to withstand summer heat and sun. Sandy soils require around half the water required by clay or silty soils to achieve the same moisture depth.

When to water
In arid and semi-arid areas, less water is lost from evapotranspiration during nighttime hours, but evening watering of lawns is not recommended because of the increased possibility of fungal disease infection. Watering between the hours of 3 and 6 a.m. is ideal, as evaporation loss is low and the grass will not remain wet too long. Consequently, an automated sprinkler system is an optimal irrigation method.

Adjust and maintain
If you have dry, discolored patches in your lawn, don't overwater the rest of the lawn to compensate for the problem; adjust the irrigation for that area by adding or moving sprinkler heads. Replace broken or cracked sprinkler heads promptly. Switch to partial heads, where appropriate, to avoid spray and wasteful runoff onto the street, sidewalk, or patio.

HOW TO GET RID OF BERMUDA GRASS TURF

Many people would like to replace some or all of their lawn with more water-efficient landscaping, but don't know how to kill off Bermuda grass or similar turf types. Bermuda grass is very tough, and cannot be killed by simply not irrigating it. You can=t rip it out or dig it up, either, because the roots go deep. Covering it with a tarp or plastic sheets to deny it water and light also is very unlikely to work. In fact, the only practical way to kill these types of grass is by using a herbicide that kills plants on contact.

The most common herbicide for killing grass is glyphosate, sold under various brand names such as Roundup (Monsanto), Kleenup (Ortho), or Doomsday (General Control). Glyphosate will kill any plant it touches, so be careful when applying it. The good news is that glyphosate decomposes rapidly, so you can plant water-efficient trees and shrubs where the grass was.

You cannot kill Bermuda grass when it is dormant in the winter. Best times to kill it are Spring and late summer.

Prior to application, irrigate your grass so that it is green and growing, so that the herbicide will move through the entire plant and kill the roots. Apply the herbicide when the temperature is 80 degrees or above, and there is no forecast of rain. Follow the directions that come with the herbicide. Using more than is recommended will not kill your grass any faster. Two days after applying the herbicide, resume irrigating the grass.

Glyphosate will kill your grass in one to two weeks. If it still shows signs of life, a second application of the herbicide may be necessary. Dead turf can be removed by setting your lawn mower very low and "scalping" it, or using a power rake.

Glyphosate will NOT kill grass and weed seeds, so you may want to apply a pre-emergent herbicide after you have removed the grass. Pre-emergents will not harm growing plants or weeds. Do not use if you plan to grow wildflowers from seed, such as California Poppies or African Daisies.