Lawns typically go dormant for the winter … but it’s not always clear if the grass has stopped growing or simply slowed down. How should we manage lawn care during the colder months? In this article, we’ll discuss how your grass grows through the winter and how to keep it healthy until warm weather returns.
Grass stops growing in winter once the soil temperature regularly dips below 50ºF (10ºC). Most grass species become dormant when the temperature dips to between 40ºF (5ºC) and 50ºF (10ºC). Warm-season species go more fully dormant than cool-season varieties at the same temperature.
Overview Of Grass Growth In Winter
Grass doesn’t completely stop all living processes in cold weather, but its growth rate can be slow enough to keep the mower in storage until spring. Some grass species tolerate cold temperatures better than others.
Note: Lawns are usually made of perennial varieties – annual grasses die each winter and must be reseeded.
In general, grass growth grinds to a stop once the soil temperature dips below 50ºF (10ºC); dormancy is initiated between 40ºF (5ºC) and 50ºF (10ºC) depending upon the variety.
The last cut of the year should be made just before the first frost. Cutting a lawn too short makes the turf vulnerable to the drying effects of chilly winds; leaving the grass too high causes it to mat down under snow and ice, trapping moisture and exposing it to molds and disease.
Incidentally, grass dies quickly if it lacks moisture, nutrients, or sunlight, but established cool-season turf can survive frigid extremes for months.
The Lawn In Winter
Living grass grows continually, but it slows down or goes dormant in cold winter weather. The plant’s metabolic rate slows during dormancy to save energy and resources. Older blades die as the plant retreats into its roots; but, as long as the crown is alive, the grass remains viable.
The ideal soil temperature for cool-season grass growth is between 50ºF (10ºC) and 65ºF (18ºC); warm-season grass does best at about 15ºF higher. Grass slows production as the soil temperature drops below 65ºF (18ºC) and initiates dormancy when it hits 40ºF (5ºC).
Unless conditions are below freezing, cool-season grass continues to produce new growth at the rate of one blade every five or six weeks. You might need to haul out the mower for a light trim during a mild winter, but you can store it away during a harsh one.
Grass isn’t damaged by its winter hibernation, and resumes growth when the weather warms up. Here are things to know:
- The referenced ranges apply to soil temperature, not to how hot or cold the air is. The ground warms up or cools down slowly: it will take a few days of chilly weather before the soil reflects the air temperature.
- Grass seed is quite resilient to cold, so it can survive a tough winter and germinate in the spring. (The seedlings and young sprouts are very tender, though!)
- A light layer of snow is beneficial for your lawn. It provides insulation for the grass while letting in light.
Factors that Affect Winter Grass Growth
Cold temperatures aren’t the only reason grass slows or goes dormant in winter. Shorter daylight hours and dry soil are other primary triggers.
Grass Variety – Unless the winters are very mild, warm-season grass goes soundly dormant over the cold months. Cool-season grasses go dormant if the temperature drops low enough but generally continue low-level root and cell development through the season.
The species of your grass makes a big difference in its winter growth. Kentucky Bluegrass handles summer but is actually a cool-season species that thrives in winter; both Creeping and Velvet Bentgrass are cold-tolerant. Improved Tall Fescue has been “improved” to better withstand heat but is well-adapted to cold winters, too.
Light – Besides growing more quickly in stronger sunlight, grass reacts to the hours of daylight. Shorter periods indicate cold weather is coming.
Water – Grass is sensitive to soil moisture. Dry soil causes it to slow down or enter dormancy; conversely, giving the lawn a deep watering is the fastest way to revive dormant grass.
Temperature – Obviously temperature is a big factor in winter growth, but your lawn’s exact response depends upon its grass variety. Cool-season grasses grow once the soil reaches 50ºF (10ºC), with an ideal range between 60ºF (16ºC) and 75ºF (24ºC); warm-season lawns thrive best about 15ºF higher.
Fertility – Your grass undergoes significant metabolic changes as winter approaches, and it needs the right nutrients to support the process. A deficiency can put the grass at a disadvantage in its struggle to survive rough weather and recover and thrive once spring arrives.
How Your Lawn Copes With Freezing Weather
Grass begins to prepare for cold weather in late summer as the days shorten and temperatures cool:
- Grass creates a winter reserve by storing carbohydrates in its roots and crown. The plant diverts energy from the leaves, which turn yellow and die as their chlorophyll diminishes.
- Cell membranes harden and increase their resistance to disruptive ice crystal formation.
- Dormant grass reduces its water content as a winterizing precaution. This partial dehydration concentrates minerals in the plant’s tissues to act as antifreeze to keep ice crystals from forming inside the cells.
Potential Wintertime Issues
Dormant grass can survive cold temperatures and still suffer winter damage!
Snow Mold
A light cover of snow shelters your grass from frigid, drying winds, but it also gives mold the moist conditions it needs to grow. These opportunistic fungi grow under snow and can kill the grass, leaving bare patches in the turf to greet you next spring.
Snow mold generally shows up in early spring as a pink- or gray-colored, crusty material on the grass. Some lawn owners resort to a fungicidal pre-treatment, but you can’t do much to stop mold once it appears.
Happily, snow mold dissipates in the strengthening sunlight of spring. You can reseed any bare spots early in the season.
Cold Desiccation
Desiccation is an extreme drying out of the plant. It can happen any time of the year, but it is particularly damaging to grass in cold weather.
Arid winter winds suck moisture from exposed turf. A worst-case scenario is when grass is stuck in frozen ground and unable to draw moisture to replace what is lost to dry, frigid winds.
Snow provides protection from wind. Exposed grass is in the most danger of desiccation. This kind of winter damage is a special problem on wide expanses of elevated turf – it’s a huge headache for golf course managers.
Windbreaks and temporary lawn coverings can mitigate the problem. Be especially alert to desiccation damage when the air temperature is 20ºF or higher than the soil temperature.
Crown Freeze
This unfortunate winter lawn disaster happens when the thermometer warms up slightly and then plunges again. It’s not uncommon in late winter as winter is losing its grip.
Increased temperatures trigger activity in dormant or semi-dormant lawns. Melting ice or snow provides plenty of moisture as the grass stirs and begins to rehydrate. But what seems a hopeful sign of spring is a setup for calamity if the weather turns cold again.
A sudden drop in temperature will freeze the newly imported water inside the invigorated grass. The expansion of internal ice disrupts the cells and can cause massive destruction. Grass damaged by crown freeze is typically limp, discolored, and dry.
The misfortune of crown freeze is that it tends to be a widespread event when it happens. The damage can affect large stretches of grass – even your whole lawn.
Crown freeze is especially common in low-lying areas with poor drainage. Improving drainage and avoiding heavy watering in the fall are the best preventatives. Gradually reduce watering as the cold months approach – and water judiciously during a brief warm-up!
Ice Cover
Even though dormant grass respires at a very slow rate, ice can block the renewal of fresh air and eventually destroy it. Grass buried in ice can survive for several weeks before it finally dies.
Like crown freeze, damage from ice cover can damage large expanses of turf. Different grass species have different survival rates for being encased in ice: Bluegrass lives about 45 days; Bentgrass may last up to 150!
Removing ice from turf without causing even more damage is difficult. If you want to go all out to save a patch of turf, insulating covers have been used to rescue small areas from ice encasement. The best prevention is ensuring adequate drainage and properly winterizing your lawn.
Footprint Trauma
Treat your frozen lawn carefully. Walking on frosty grass, especially on young, freshly seeded grass, can severely damage it. The results are brown disruptions in the turf. The full damage may not appear for several days.
Grass uses its internal antifreeze mechanism to minimize the formation of internal ice crystals, but the pressure of exterior ice can puncture and shred its cells, killing plant tissue. Walking on frozen grass can leave patches in the lawn for months.
Winterizing Your Lawn
With proper preparation, your grass can avoid most wintertime problems and emerge healthy and ready for spring.
Yard Clean-up
Fallen leaves and other organic debris can smother grass. Remove excess matter from the lawn before cold weather sets in!
Pre-Winter Mowing
There are two aspects to mowing during the countdown to winter:
Grass Height – Your lawn should enter the cold months with a moderately short cut. This is often a bit shorter than its summer-growing height. Mowing too close will leave the grass exposed to the harsh weather, while grass cut too high tends to flatten and trap moisture that invites mold.
Don’t lower your grass’s height drastically in the final weeks. Gradually bring the turf to the appropriate height starting in early fall.
Timing – The other important factor is timing. Watch the weather reports! The goal is to make your final mow of the year just before cold weather arrives.
A robot mower can be helpful in getting the timing down. It can make frequent cuts until winter sets in, leaving your lawn in the best shape possible.
Lawn Mower Winterization
Two simple tasks can protect your lawn mower over the winter.
Clear the Deck – Remove all grass clippings or other material stuck to the underside of the mower. Organic matter attracts moisture and corrosion. Disconnect the spark plug or battery as a safety precaution before cleaning.
Add Fuel Stabilizer – Fuel left in the mower can attract moisture and contaminants and will degrade during long-term storage. Adding fuel stabilizer to the mower’s tank before putting it away for winter can save you a headache next spring.
Overseeding
Either early or late autumn are great times to overseed your lawn. Don’t do it in the middle of the season because the grass seedlings will still be maturing when cold weather hits. If you miss the first opportunity to sow, wait until just before the first frost.
Late summer/early fall sowing is effective because grass grows so well in the temperate days of autumn. It generally takes only one or two weeks for the grass to germinate. The tender seedlings can mature in the mild days of autumn and be ready for winter.
Late fall/early winter sowing is also called “dormant seeding.” Grass seed is made for surviving cold winters; the seeds nestle into the turf and endure the winter before sprouting with the moisture and warmth of spring.
The ideal preparation for seeding is to first mow and then aerate your lawn. The seeds that fall into the holes left behind by the aerator will be nicely protected for germination.
Final Fertilization
The best time to give your lawn its final fertilization varies from year to year. Let the grass tell you! The ideal time to feed is after the blades have stopped growing but before they turn yellow or brown.
It may be a short window, so watch your lawn carefully as the weather cools.
Winter Lawn Tips
- If your winter is mild and the grass has added some height, it’s fine to give it a trim. Mow when the lawn is dry and the temperature is over 40ºF (5ºC), and only make it a light cut.
- Don’t use salt to de-ice your lawn – it can dehydrate and damage the grass. Use sand or cat litter as a safe alternative.
- Don’t burden the grass with extra snow or ice from shoveling. A heavy cover of snow can kill the grass.