How Do I Water My Landscape Correctly?

Deep and infrequent watering is best for healthy trees.

Published January 28, 2010, By SARAH SOURS

It would be wonderful if there were a simplistic answer to this question. The most uncomplicated answer is to water deeply and infrequently averaging one inch of water a week during the growing season. This watering method allows for more oxygen in the soil, deep and healthy root systems, fewer occurrences of diseases, and lower water bills and responsible use of water.

To accomplish deep and infrequent watering, use one or both of these methods:

• Dig a small hole and feel the soil. If it is moist within the first four inches of soil depth, watering is not needed.
• Calibrate your irrigation system to deter­mine how long and often you need to water. To calibrate your sprinklers, you will need to follow two steps.

Step 1. Measure how much water is emitted from your sprinkler system in 30 minutes. Pick a day when the soil has been dry for several days. Scatter three or four shallow cans (such as tuna cans) through one sprinkler zone. Make sure the cans are identical. The more cans you place the more accurate the measurement will be. Turn on that sprinkler zone and allow it to run for 30 minutes. Once you turn off the system, collect the cans, and pour all of the water into one of the cans. With a ruler, measure how many inches of water are in the can. Divide the total inches of water by the number of collection cans. This will tell you the average amount of water applied to your landscape during the previous 30 minutes.

Example: Four cans were placed in a zone and the sprinklers ran for 30 minutes. The water was poured into one can and the water measured two inches. Two inches of water divided by four cans equals one half inch of water in 30 minutes. (two inches of water/four cans = half an inch) This means you could water twice a week for 30 minutes each time to accomplish the one inch of water a week rule.

Step 2. Use a small shovel or hand trowel to dig a hole or part the soil for gauging how deep the water penetrated into the soil during the 30 minutes. The goal is to wet the top six inches of the soil. If water is not absorbing into the ground, but running off into the sidewalk and street, you may need to water in two cycles to acquire the right depth of moisture. If water is beginning to run off after 15 minutes, do not run the zone for more than 15 minutes at a time. Allow at least 30 minutes to an hour for the soil to dry. Then run the zone again for the last 15 minutes interval to allow the soil to absorb the water to the desired depth of six inches. Follow these same steps for each zone.

When the soil begins to dry and indicator plants, such as grass, begin to lie down and look less green, check the soil for moisture. If it has dried within the first four to six inches, it is time to water again.

Most plants will grow well with one or two waterings a week, adding up to one inch of water during the growing season. Always compensate for any rainfall in your watering schedule. If you have high-water demanding plants such as hydrangeas or impatiens that are drying out more quickly than the rest of your plants, consider hand watering them, or removing them and planting a more drought tolerant plant. Over time, the excessive watering of a 60 year-old Red Oak to keep a flat of flowers alive will result in losing the tree.