April and May can be very dry months averaging only 2.03 inches of potential rain fall. Add to that the higher temperatures, low humidity and wind and you end up with a high evapotranspiration rate. Evapotranspiration (ET) is a process by which water is transferred to the atmosphere from vegetative surfaces. ET consists of two components, evaporation and transpiration. Evaporation is a physical process by which water is changed from a liquid to a gaseous state. Evaporation takes place from free water surfaces such as ponds, streams, wet soils or wet vegetation. Transpiration, the other component of ET, is a plant process of water loss. That is where the term evapotranspiration came from.
Here in South Florida our sandy soils can experience drought conditions after only a few days without rain. This condition is made worse by high temperatures. In order for our lawns to survive with little or no water they must be conditioned before a drought occurs. Supplemental irrigation usually provides adequate water for lawns between rainfalls. But in the past water management districts have enforced severe water restriction schedules, allowing watering only once a week or less. We are under a twice a week restriction now. It is important to prepare your lawn for drought now so it will survive such severe restrictions as you never know when a drought will occur.
Your primary objective is to grow a good healthy lawn that will survive with little or no supplemental irrigation. A properly prepared lawn will have a deep, extensive root system that can withstand the stress of such reduced irrigation. This can be achieved through proper management practices.
Proper irrigation is the first step. Frequent, light watering can cause shallow root systems that are not good for a healthy turf. To develop a deep root system, water only when the lawn shows the first signs of wilt. This means twice a week at most and preferably only once a week. Then apply enough water to wet the soil in the root zone, approximately one inch.
Knowing the amount of water your sprinkler system applies to your lawn is an important step in using water efficiently. Most people irrigate for a given number of minutes without knowing how much water they are really applying. Use this method to determine how long to irrigate to apply one inch to your lawn.
Calibrating or determining the rate of water your sprinkler system applies is an easy job.
- Obtain five to ten coffee cans, tuna fish cans or other straight sided containers to catch the irrigation water. Containers three to six inches in diameter work best.
- Place the containers in one zone at a time. Scatter the cans at random within the zone. Repeat the entire procedure in every zone because there may be differences in the irrigation rates.
- Turn the water on for fifteen minutes.
- Use a ruler to measure the depth of water in each container. The more precise the measurement, the better your calibration will be. Measurements to the nearest eighth of an inch are adequate.
- Find the average depth of water collected in the containers by adding the depths and then divide by the number of containers.
- To determine the irrigation rate in inches per hour multiply the average depth of water times four.
Try to calibrate the system during the same time the system is normally run so that water pressures are similar. Low water pressure can significantly reduce the amount and coverage of water applied by a sprinkler system. Never apply more than one inch of water per irrigation. Avoid mixing sprinkler head types. Mist heads apply more water than stream and rotor heads. Match sprinkler heads for uniform coverage. Check your system frequently. Replace broken heads, clear clogged nozzles and adjust the direction of spray. Now that you know your sprinkler system irrigation rate, you can more efficiently apply water to your lawn.
It may take up to six weeks to condition your turf to survive several days or more without wilting between irrigation or rainfall. During this time the root system is developing and growing deeper into the soil.
Proper mowing practices are also essential for a drought prepared turf. Every time a lawn is mowed the grass is stressed which reduces root growth. Mowing frequency and height of cut should be carefully considered. The majority of lawns on Marco Island are being cut too short. Use the highest setting on the mower as a short cut will stress the turf. By increasing the grass leaf area, more photosynthesis can occur. This means more carbohydrates for plant growth, especially root growth. The higher the height of cut on a lawn the deeper and more extensive the root system will be. Adjust the frequency of mowing to the growth of the turf. At least once a week in summer, while once a month may be enough in the winter. Try not to cut off more than a third of the blade with each cut. Also, keep the mower blades sharp. A clean- cut leaf blade will heal more quickly and thus lose less water than a shredded blade.
Proper fertilization practices can enhance the drought tolerance of grass. All the drought conditioning accomplished by proper irrigation and mowing practices may be eliminated by excessive nitrogen fertilization. Shoot growth is enhanced and root growth reduced by excessive nitrogen. Drought conditioning can only be accomplished by applying just enough nitrogen to obtain a small, but continuous, amount of growth. Lawns should never be fertilized to deepen the green color since St. Augustine grass is naturally more yellow-green. Potassium fertilization promotes increased root growth and thicker cell walls. Drought tolerance is improved by applying potassium. Grass requires potassium in nearly the same amount as nitrogen, especially in sandy soils where both can readily leach out. In times of drought a 15-0-15 lawn fertilizer would be preferable over a 16-0-8 analysis. In addition, the palms in your landscape require more potassium than nitrogen and would also benefit from the higher potassium content in your lawn fertilizer.
Pest control on lawns should be done with great care during the hot, dry spring months because pesticides can add extra stress through phytotoxicity (chemical damage to plants). Pesticides should never be applied on a preventative basis. When a pest problem is diagnosed however, it should be treated appropriately as necessary. Spot treatments can be as effective as treating the whole lawn. Be particularly watchful for insects and diseases which attack the grass root systems such as grubs or root rots.
If you have areas in your lawn which will not survive without extraordinary care consider using mulched beds, shrubs and ground covers which do not require supplemental irrigation.
Even if we begin to have a lot of rain, we should not squander our water. Prepare your lawn for drought and save our valuable water resources every day of the year.