Watering Lawns in Summer

Watering Lawns in Summer

Tom Ingram: Ask A Master Gardener

Tuesday, July 25, 2017

Q: It’s so hot outside. How do I know how much I should be watering my lawn? E.K.

A: If your lawn is Bermuda grass, it needs about 1 inch of water per week this time of year, while fescue needs about double that or 2 inches of water per week. This answer usually leads to another question: How long do I run my sprinkler? The answer to that question necessitates you doing what we call a “simple irrigation audit.”

For a simple irrigation audit, you are going to need nine collection cups, pen, paper and a calculator (at least most of us will need a calculator). Collection cups can typically be purchased from an irrigation supply store or you can use clean metal cans that might previously have contained tuna, cat food or perhaps tomato paste. Using the same type of can for all your collection cups will make your data more reliable.

If you choose cans, you can use a ruler and a fine-tip permanent marker to mark the outside of the cans in ¼-inch increments. Or you can just measure the collected water by sticking a ruler directly into each collection can.

To collect your measurements, locate your nine collection cans about 8 feet apart in something close to a 16-by-16-foot grid.

Next, let your sprinkler run over your collection grid for 20 minutes. After the collection period is over, measure the amount of water in each of your collection cups, add up the total amount collected (calculator time) and divide the total by nine because you were using nine collection cans. This will give you an average amount of water your collection grid area received in 20 minutes.

So let’s assume your average measured amount was ½ inch. This means for every 20 minutes your sprinkler system runs, your turf will be receiving half of an inch of water. If you have Bermuda grass, which needs 1 inch of water per week, you are going to need to water 40 minutes per week. You can split this up into two watering sessions per week of 20 minutes each.

If you have a fescue lawn, which needs 2 inches of water per week, the math says you would need 80 minutes per week, which can be split up into two watering sessions of 40 minutes each.

Garden tips

• Spider mites are a difficult pest to deal with, and they love hot, dry and dusty weather. One of their favorite targets are tomatoes, where they cause a stippling or sandblasted appearance on the leaves. They are small but may be seen if you tap a leaf over a sheet of white paper and look for moving dots. Treat with jets of water to wash them off and use either horticultural soap or oil according to directions. Neem oil is a good choice for a safe organic insecticide. If you use an insecticide of any sort, it is best to spray  early or late in the day, when honeybees are in their hive.
• Tomato growers are aware that fruit production usually stops in the heat of summer. Most tomato pollen becomes infertile and blossoms drop off when night temperatures are above 70 degrees and daytime is above 92 degrees for a few days. This also occurs in peppers, some varieties of beans and other vegetables. As it cools in late summer, fertility returns. If your tomatoes are too tall and gangly, you may cut them back a third. New growth and fertile blossoms will develop when it cools in fall.