Grass Height: The Long and Short of It

Brad Wier

How often you mow and how short you cut the grass can determine how much water you save — or waste.

We hear it all the time, and I mean all the time: raising the lawnmower blades means the grass needs less water!

It’s not often you hear that mowing your grass can save water. So here’s the long and short of mowing, blade height and watering.

  • Frequency: With warm soil temperatures and recent rains, grass grows quickly in early summer — much more quickly than in winter. As a rule of thumb during the South Texas growing season, keep Bermuda grass one inch high, zoysia a bit longer at two inches and St. Augustine grass at three inches. St. Augustine, always a little thirstier than the others, uses that extra height to support deeper roots. Mowing height doesn’t make that much difference to Bermuda grass beyond appearance, but recent studies suggest that, unlike Bermuda grass and fine-blade zoysia, ‘Emerald’ zoysia’s water requirements actually increased with blade height.
  • Blade height: When the grass is growing quickly — especially after May and June rains — raising the blades is a mechanism to keep it dense without having to increase the mowing frequency. Here’s why: it’s important when mowing not to cut off more than 30 percent of the leaf surface at any one time. Otherwise the turf, having lost so much of its photosynthesizing surface area, will spend more time and effort trying to rebuild its leaves. If your St. Augustine has grown to 5 inches and you cut it down to 2 inches (60 percent), prepare for weeds to begin to penetrate and spread in the newly exposed areas around the soil surface.Remember, though, if you raise the blades too high, the grass can start growing really, really long, reaching for light — alarming your neighbors, and resulting in even more damage and weed penetration the next time it’s cut. Don’t overdo it when raising the blades; one or two notches should be sufficient. Depending on the mower, there’s often no better way to tell than just measuring the grass blade after cutting.
  • Supplemental irrigation: If you’re watering your grass on a weekly basis, you may already have all the humidity you can stand, but many SAWS customers elect to run the sprinklers twice a day in summer. (A few extremely generous ratepayers do this all year long!)Problem is, too much water drives air out of the root system and makes it difficult for grass to take in more water (or nutrients.) As a rule of thumb, it’s best to wait until the surface of the soil is dry to the touch before applying more water.

Instead of running the entire sprinkler system morning and evening, determine which sections seem to require more water and run your system accordingly. As always, SAWS Conservation offers free irrigation consultations to customers interested in the most bang for their water bucks.

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