How to Protect St. Augustine Grass Before a Freeze in Houston

How often Houston actually freezes

St. Augustine is one of the least cold-tolerant warm-season grasses grown in Texas, according to Texas A&M AgriLife. That's the trade-off for how well it handles our heat and shade. The good news is that most Houston winters only test it lightly.

Using NOAA's 1991 to 2020 climate normals for Bush Intercontinental, the middle date for Houston's first 32 °F night is about December 9, and the middle date for the first hard freeze (28 °F or colder) is about January 2. About one year in ten, the first freeze comes before November 17. So a November cold snap isn't unusual, and that early one is often the one that catches people off guard. Get the fall winterizer down in the first week or two of November, while the grass is still growing, so that job is finished before a cold snap. See when to apply winterizer.

Frost vs. freeze: why it matters

AgriLife separates two kinds of cold events, and they call for slightly different thinking:

• Radiative frost: clear sky, little wind. Heat escapes from the ground at night and frost forms on the grass, even when the official low stays above 32 °F. Low spots in the yard get it first.
• Advective freeze: a windy cold front (a blue norther) that drops temperatures fast and can last a day or more. These are the ones that do the most damage, because the cold and the drying wind go on for hours.

A frost usually just browns the tips and speeds up dormancy. A long, hard freeze is what kills runners, especially in exposed spots and on lawns that were stressed going into winter.

The day before: what to do

1. Check the soil moisture. Push a soil probe into the lawn in a few spots. If it slides in easily and comes out damp, you're fine. If it's hard going and dry, water.
2. Water if it's dry, a day or so ahead. AgriLife's frost guide recommends watering the soil the day before a frost night. Wet soil captures heat during the day and releases it at night, and water gives off heat as it freezes. The grass also holds up better when it isn't drought stressed on top of the cold. Aim for a normal watering, not a flood.
3. Get it done while it's above freezing. Water early enough that the lawn isn't sitting in puddles when the temperature drops. Once it's already freezing, don't run the sprinklers. Water can't be taken up by the roots then, and ice on sidewalks and driveways becomes a safety problem.
4. Clear off leaves and debris. A mat of wet leaves isn't a blanket. It holds moisture against the grass and invites disease. See leaves on St. Augustine.

Should you cover the lawn?

For an established lawn, no. Covering a whole yard isn't realistic, and a healthy dormant lawn doesn't need it for a normal Houston freeze.

It can be worth it in two cases: new sod laid this fall, and small thin or exposed patches you're worried about. If you cover:

• Use a breathable frost cloth (row cover), old sheets, or burlap.
• Anchor the edges to the ground so it traps heat coming up from the soil.
• Skip clear plastic sheeting. AgriLife notes that it cools quickly at night and can damage what it touches.
• Take it off once temperatures climb back above freezing the next day.

Caring for sod that went down this year? See new sod care.

Protect the sprinkler system and hoses

The lawn usually comes through a freeze better than the plumbing does.

• Turn the irrigation controller off (or to rain mode) so it doesn't run in the middle of the freeze.
• Wrap the backflow preventer and any exposed pipes with foam pipe insulation or an insulated cover. It's a cheap step that can save a costly repair.
• Disconnect hoses from the spigots. A hose left attached can trap water in the faucet. With a quick connect kit on the spigot, pulling the hose takes a second. I drain mine and roll it up on a Hoselink reel.
• Turn it back on afterward. If it's been warm and dry for a couple of weeks after the freeze, a dormant lawn still needs an occasional watering.

During and right after the freeze

• Stay off frosted grass. Frozen blades break when you walk on them, and the footprints can show up as brown tracks.
• Don't mow short to clean it up. Scalping a cold-stressed lawn makes recovery harder. When it's time to mow again, keep it at 3.5 to 4 inches. See mowing height.
• Don't fertilize to green it up. AgriLife's Galveston County office is blunt about this: feeding a lawn after a freeze does more harm than waiting for spring. Your fall winterizer should already be down before the cold arrives. See winterizer for St. Augustine.
• Skip weed and feed. Spot treat or pull winter weeds instead.

Warm spells make freezes worse

Houston winters swing. A week in the 70s can wake the lawn back up, and AgriLife notes that plants that de-acclimate during warm stretches are more vulnerable when the next cold front hits. You can't control the weather, but you can avoid adding to the problem: no heavy nitrogen late in the year, no scalping, and a lawn that isn't bone dry when the cold arrives.

If it turns brown

Brown after a freeze usually means dormant, not dead. Don't judge it in January. Wait for spring green-up, then repair only what didn't come back. Here's how to tell dormant from dead.

Common questions

Should I water my St. Augustine before a freeze?

Yes, if the soil is dry. Water a day or so ahead, while it's still above freezing. Moist soil holds and releases more heat than dry soil, and the grass handles cold better when it isn't also drought stressed. Don't run sprinklers once temperatures are already at or below freezing.

Should I cover my St. Augustine grass during a freeze?

For an established lawn, no. It isn't practical and it's usually not needed. For a small area of new sod or a thin patch, a breathable frost cloth anchored at the edges can help. Avoid plain plastic sheeting, which can do more harm than good.

What temperature kills St. Augustine grass?

There isn't one number. Damage depends on how cold it gets, for how long, whether the grass was dormant or still green, and the variety. A typical Houston frost won't kill a healthy lawn. Long, hard freezes like the February 2021 storm are what cause real winter kill.

Can I walk on frosted St. Augustine?

Try not to. Frozen blades break when you step on them, and footprints can show up as brown tracks later. Wait until the frost melts off.