Irrigation Basics - The how's, why's and when's of watering

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I asked my GardenLine Facebook family what I should write about this week - other than sod webworms -- and several suggested the rules of watering lawns in the summertime.

How much and how often should you water your grass? Sounds like a pretty basic question, but the answer isn't simple.

Irrigation needs depend on many factors - the kind of grass you have, your soil profile, mowing height, and the kind of watering system you have. Plus, of course, what Mother Nature doles out, so my basic irrigation schedule takes temperatures and rainfall into consideration.

Normally, turf and landscapes in the Houston area do fine with 1-1½ inches of water every seven days when daytime temperatures are in the 70s and 80s. As daytime highs hit 88-92, you can probably up that to 1-1½ inches every four to five days. And when thermometer readings exceed 93 degrees consistently (normally July-August), you should probably water every two to three days.

However, I've learned over the past 15 years that the more compost you use as top dressing, the more drought-tolerant your lawns and landscapes can become. In other words, the more organically-enriched the soil is, the less water you need. Several colleagues I know in the soil business have not even run their irrigation in summers that included mini-droughts.

The kind of grass you have is also very important. St. Augustine needs the most water, Bermuda a little less, and Zoysia far less. However, your soil is the most critical factor. Clay or sandy soils not very well enriched with organic matter definitely need more water because they dry out quicker. So, add more organic matter like, compost.

As for when to water, I always say early in the morning. That's when water pressure is at its best, there's less wind to evaporate the moisture, and the turf will be able to store up water for the warm day ahead. If you have automatic sprinklers, schedule them to run between 3 and 8 a.m. Start manual sprinklers when you first get up. If you water at night, you run the risk of suffering fungal diseases like brownpatch.

And how long does it take for your system to put out an inch of water? Place an empty tuna or cat food can at the farthest point the spray pattern reaches. When it fills up, that's how long it takes. Depending on the system, that range from 15 to 45 minutes.

If it seems your neighbors don't run their sprinklers as much as you, they just may have more organic matter in their soil. And remember, rich, organic soil doesn't happen overnight. Compost, enriched topsoil, or soil activators need to be added consistently each year.

Finally, if you aren't mowing as tall as your lawnmower will allow, make the change today — unless you have a Bermuda or thin-blade Zoysia lawn. Tall grass in good soil develops deeper roots which draw a larger volume of deep moisture, requiring less supplemental irrigation. Plus, lawns mowed tall provide shade that can reduce unwanted vegetation. Bermuda for example, is a low-profile grass, and if shaded by St. Augustine, it won't proliferate.

There is one caveat to all this, however. Newly sodded lawns need to be watered on a daily basis during the heat of summer. Keep the "mud" wet under the root zone so it will break down and allow roots to establish in the soil below. Don't drown the new sod ... just keep it moist enough to soften the soil and help the roots grow down.

If you need any more clarification on this subject, or you want to take issue with any of my rules, please give me a call this weekend on The GardenLine. The number is 713-212-KTRH (5874).

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