Optimal time settings for in-ground sprinklers

I have a built-in sprinkler system and just had some service done yesterday. The tech said I should set the zones for 20 minutes each three times a week. But everything I’ve always heard was one deep watering (1" of water) once a week is better than multiple shallow waterings. Twenty minutes for one of those zones is probably 1/4" of water.

Who’s right?

Put a cup or something to measure the amount of water a 20 minute sprinkling puts out. While generally speaking you do want a good soaking what you don’t want is the water pooling. I see you’re in VA but I don’t know what your soil conditions are. You can probably check your county extension office and see what they recommend.

It depends. Are we talking about a grass lawn or some other kind of planted area? Most drought resistant plants don’t need that much water, while others plants may quickly die without it.

If we’re talking about grass, you may need to factor in air temperature and humidity to determine how much water is appropriate in your situation. If you have a neighbor with a similar setup, and they seem to be having good success, you may want to ask them what their watering schedule is.

Most people tend to over water, which wastes water and causes it’s own issues.

FWIW, I water my lawn and planting beds 4 times a week (every other day), for 15-20 mins each, and that seems to work out pretty well for me, however YMMV.

I was also told morning was better than evening, because in cooler conditions soaking wet overnight can encourage mold growth.

May also depend on the current weather (and soil conditions). Letting the ground get bone dry in searing heat for a few days is also probably not healthy.

If you water in the evening, the water will sit on your grass and plants all night, which can lead to mold. It’s better to water in the wee hours of the morning, before it gets hot. That way, it’s cool enough that the water can soak in well, but any residual water left on the grass will evaporate as the sun rises.

Time will depend on your soil. Sandy soil drinks water in quickly, but doesn’t hold on to it very long. Clay-like soil absorbs water slowly, but holds on to it for a long time. Loamy soil is the optimum mix of both. One way to test how your soil absorbs water is with a can; cut out the top and bottom and push it partway into your soil, add an inch of water, and check it in half an hour. If it’s gone, your soil is very sandy; if it’s hardly absorbed at all, your soil is very clay-like. If it’s half gone, you’re in good shape.

Optimally, you want to give your lawn an inch of water a week. It’s best to give the water in two waterings of half an inch each; that gives your lawn plenty of water to live on, but also gives it time to dry out between waterings. Before we were on water restrictions, I would water on Monday and Thursday, which left the lawn and garden dry enough to work on during the weekend. If your soil is very clay-like, you may have to do two short waterings on each day, with some lag-time in between, to get the full amount completely absorbed.

Oh yeah, one more thing: mow high. I know people think short, even grass is prettier, but the grass won’t be as healthy, because it’ll have to put more effort into regrowing its leaves rather than getting richer and denser. Also, long grass means more shade at the ground level, which means it’ll be harder for weed seeds to germinate.