Fall is a more active growth season than most people usually think. It’s the best time to plant trees, cool-season grasses, and winter vegetables, while all the decaying plant material means bioactivity in the topsoil. There is a lot that plants and animals do in preparation for hibernation through the low-temperature months.
For your lawn, this means storing as much energy as possible before winter dormancy. As cold temperatures approach, you may wonder at what temperature you should stop watering grass. Once daytime temperatures reach a consistent 40 degrees and below, it’s getting too close to freezing to continue watering the lawn, and you should stop for the season.
Watering In The Fall
Cool-season grasses that are preparing for a winter dormancy will need lots of water throughout the fall season to store enough energy in their roots to use throughout the cold weather.
50 degrees isn’t too cold to water grass, but as the temperatures drop closer to freezing, you can help guide your grass to a healthy dormant state by paying attention to the weather forecast.
Frost And Grass
As temperatures start to lower at the end of fall, frost in the morning is a sign winter is on its way. The National Weather Service uses 36 degrees Fahrenheit as the threshold for potential frost, a bit higher temperature than freezing.
Wind and darkness can keep an area especially cool at the surface level late at night and early morning, causing grass-level air temperatures to reach freezing without the ground itself freezing. Frost happens when condensation from water vapor in the morning air, or dew, freezes directly on contact with a frozen blade of grass.
Normal, light frosts won’t kill your mature lawn. As long as you don’t water when frost is present, it’s OK to water grass when it’s cold as long as it’s above 40 degrees since it won’t freeze the ground or roots.
Regular frost, however, or watering when frost is present, can damage the cells of the grass blades or roots from the freeze. You should also avoid walking over frosted grass since it is brittle and can easily be damaged from being bent and compressed.
One way to prevent frost in your yard while temperatures are still above 40 is by watering in the evening. Putting the sprinkler out or setting your watering timer for 7 pm will give the soil moisture to:
- Hold heat to radiate – Moist soil holds heat since water is a conductor and stores energy
- Keep the blades warm – When the blades of grass aren’t frozen, water vapor won’t freeze to them
- Raise the air temperature – warm soil will evaporate moisture and raise the surface-level air temperature
Too much frost can damage grass blades when water expands to ice at the cellular level, damaging the structure and preventing the blade from performing photosynthesis.
Newly sprouted grass is very vulnerable to frost and freezing, so if you’re planting new seed this fall, be sure to sow four to six weeks before the first frost for your grass to grow to a mature size and be able to withstand the cooling temperatures.
How Cold Is Too Cold For Sprinklers?
When it’s below 40 degrees and too cold to water the yard, you can put the sprinklers away or turn them off for the year. Running your sprinkler during near-freezing or freezing temperatures can damage your hose and irrigation system, as well as the sprinkler itself since water expands when frozen and may crack the hose or sprinkler material.
Is My Grass Dead Or Dormant?
At the end of the fall season, even if you’ve been watering throughout fall, your green lawn will eventually fade to brown as it goes dormant. Still, you want to be sure that the grass isn’t dying, just entering dormancy.
If you see brown or yellowing patches on the lawn, it’s something you should look into. When grass goes dormant, it does so uniformly across the yard. Another sign that the grass hasn’t died is when it regrows in spring.
Should I Water My Lawn During The Winter Months?
By winter, air and soil temperatures will be too cold for grass and most plants to grow. It’s best to avoid watering the lawn between the end of November and the end of March. When your grass stops growing in late fall, it’s a sign it’s entering dormancy.
Dormant grass doesn’t need much water in the winter, a time when very little water and nutrients are available. Moisture in topsoil will be frozen while air temperatures are consistently below 32, and the roots will stop absorbing as much water.
During the normal growth periods in warmer months, mature grass needs about an inch of water per week. During the winter, grass needs about a half-inch per week and will get most, if not all, of it from groundwater, rain, and snow.
How Soon After A Freeze Should I Water My Grass?
In transitional months, weather can be variable, with some nights freezing and other nights staying above 40. If there was frost this morning and there hasn’t been for a day or two, and the next few days are forecast for 40 or above, watering in the evening or the morning can be fine. Just be sure not to over-water in case the outlook changes, and keep your eye on the report.
When there are days back to back below 40 degrees, you should avoid watering. As it warms in spring, you’ll start watching for back-to-back daily temperatures above 40. When days are consistently above 40 degrees, you can begin watering the ground again to encourage regrowth of the dormant roots.
Warm air and soil moisture temperatures will trigger blade growth in root systems and germination in newly planted seeds, but be sure not to plant until spring frosts end. Freezing temperatures can prevent seeds and sprouts from receiving enough moisture to grow, and planting too late in the fall or too early in the spring takes the risk of a surprise frost.