Pensacola News Journal

For: Saturday, May 26, 2001

By: Daniel E. Mullins

Extension Horticulture Agent

Santa Rosa County

Fine Tune the Irrigation System Using the Can/Pan Test

It’s time for gardeners to take a close look at current lawn and landscape irrigation practices and make sure that water is being used wisely. We are into our third year of drought along the northern Gulf Coast, and the consequences are beginning to show.

Water levels are dropping in shallow irrigation wells. Salt water intrusion has been found in some coastal wells and the threat of use restrictions by public water systems looms, if the drought continues.

Established lawns and landscapes need not be watered daily. Deep, infrequent irrigation is better than frequent sprinklings. Two irrigations per week are usually sufficient except during extremely hot, windy periods.

The amount of water that is applied at each irrigation is as important as the frequency. Unless the irrigation system is calibrated, I dare say that even an experienced gardener might not know how much water is being applied.

I frequently ask homeowners how much water that they apply during each irrigation. Invariably, the answer is given as the number of minutes that the sprinkler system runs.

The time of sprinkling means nothing, unless there is a correlation between that and the volume of water that is applied. I have seen systems that could deliver the required amount of water within 20 to 30 minutes, while others would take over two hours to deliver the same amount. The amount of water that is delivered by an irrigation system is determined by pipe size, pressure and the number of specific sprinkler heads that are used.

Since no two irrigation systems are the same, each one should be calibrated in order to determine the exact amount of water that is being applied. Established lawns, on sandy sites, should be given ½ surface inch of water, while shrubs require about 3/4 of an inch at each irrigation.

One-half or three fourths of an inch of water is a lot of water given the fact that one inch of rainfall or irrigation amounts to 27,000 gallons of water per acre. Using a one quarter of an acre lot as an example, there would be approximately 7,000 square feet left in lawn and landscape plantings following construction. Over two thousand gallons would be required to deliver one-half inch of water to this sized lawn area.

The Can or Pan Test

Find out how much water your system is delivering and make any necessary adjustments. This can be easily done by placing 5 or 6 straight sided cans or pans at random throughout the area to be irrigated. Run the system a predetermined amount of time and, using a ruler, check the depth within the pans.

Continue to check the pans and keep up with the sprinkling time until an average of one half inch is collected in the pans. A longer, but less frequent cycle will be needed for shrub plantings, which require three fourths of an inch.

Most gardeners who perform this relatively simple test are shocked by the results. In many cases it is determined that only a fraction of what is needed is being delivered. On the other hand, the system is sometimes found to be delivering excessive amounts of water which is wasted.

Question of the Week: No matter how much that I water, certain spots in my lawn seem to wilt soon after irrigation.

Answer: Wilted spots in lawns - those light gray, sickly looking areas are showing up more and more as the drought continues. First, check to see if your sprinkler pattern is overlapping properly and providing uniform coverage. This can be done using pans, as described above.

A second cause could be differing soil textures within the lawn. Sometimes differing textures of soil are used for filling different areas during construction. In other words, the spots that dry out more quickly could be because the soil is more sandy, or porous in those areas. If this is the case, consider watering these areas with spot watering sprinklers between regular irrigation times, instead of watering the entire lawn.