Mulch is a gardener’s best friend. Mulch, often shredded bark, straw, or leaves, is important to use in your garden. This organic material keeps moisture in the soil, regulates soil temperature, and suppresses weeds. In the winter, it’s important to protect your plants, even if there is less growing in the garden by putting a layer of mulch around them. We spoke to gardening experts about why mulch is important in the winter in the South, when to apply it, how much to apply, and the benefits of mulch.
Why Mulch Is Important In The Winter
Mulching provides numerous benefits to a garden year-round, including regulating the soil temperature, minimizing evaporation in the soil, and protecting the roots. “Mulch is an essential part of gardening year-round,” says Justin “Jules” Giuliano, Lead Soil Researcher at Rosy Soil. “In the winter, especially, it serves to keep the soil warm and the soil microbiology alive.”
Climates are changing across the globe. Regions that didn’t have extreme weather patterns or cold or harsh winters may now encounter freezing temperatures. “The South can no longer count on the mild winter patterns we once knew,” says Tammy Sons, CEO and Founder of TN Nursery in Altamount, Tennessee and a National Garden Bureau member. “In recent years, we’ve been hit with sudden, extreme cold snaps that resemble the conditions of zones 3–5,” says Sons. The changes can occur in short bursts, but the damage is done to traditional zone-7 plants, he says.
When To Apply Mulch For The Winter
Apply mulch before the cold and icy or snowy weather arrives. Check your geographic hardiness zone for an idea of when the first frost occurs. “We typically start mulching after the first frost has passed,” says Sons. Mulching is done by hand so he chooses a sunny day with mild temperatures. “Homeowners should wait until temperatures drop below 50 degrees at night to mulch, which usually occurs in September-October for most climate zones,” Sons adds.
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Before a big change in weather or a drop in temperature occurs, make sure to put mulch around your plants. “If you’re anticipating a dramatic change in temperature, such as a polar vortex or deep freeze, applying mulch before the freeze sets in can make a major difference in helping your plants weather the cold,” says Jim Putnam, plant expert on behalf of Southern Living® Plant Collection.
How Much Mulch To Apply In Winter
Garden experts tend to apply around two inches of mulch, but each has their preference. “I like to add a mulch layer that’s about 1-2 inches deep in the winter to really insulate the soil,” says Guiliano. “Anytime the mulch falls below that, reapply some more,” Putnam says.
You don’t need deep layers of mulch in the fall and winter. “An inch and a half to two inches is plenty and helps avoid the problems that come with piling it on too thick,” he says. While Sons usually adds 2-3 inches deep of mulch around the plant’s base.
Choose organic mulch, which will add nutrients to the soil as it decomposes.” “Save your old leaves, pine needles, and plants from your fall garden to use as mulch,” says Giuliano. He rarely buys mulch and prefers to use what he has around him. “If you are buying mulch, opt for organic mulch that hasn’t been artificially colored as that will seep into your garden soil,” he adds.
What May Happen Without Mulch
Forgetting or not applying mulch could cause some plants to die or not survive a harsh winter. “You may lose some plants in a frost if the root zone is impacted,” says Guilano. “Some of your root crops like radishes, turnips, and garlic may suffer initially as they’re growing to full maturity.”
Weather is becoming unpredictable and unexpected frosts or sudden changes in temperature can negatively impact your garden without much warning. “In 2023, we lost thousands of nandinas and boxwoods during six days of the coldest temperatures I’ve ever seen here, dropping as low as –9°F,” says Sons. “The areas that weren’t mulched suffered significant losses.”
Applying mulch is key to protecting your plants from unexpected cold fronts or freezing temperatures that may not have been common for your geographically hardiness zone. “The same varieties planted on the north side—where we had applied proper mulch—survived the harsh conditions without issue,” explains Sons. “It was a powerful reminder of how essential winter protection has become in the South.”
Benefits Of Mulch
Mulch provides many benefits for the soil year-round. Here are some reasons why you want to use mulch to protect your plants.
Maintains Soil Temperature
Mulch creates a layer over the soil, providing insulation and regulating the soil temperature. “Mulch is essentially a blanket for the soil,” says Putnam. Having a layer that keeps the heat in is crucial during the winter months when the soil can freeze.
“It traps the residual heat already in the soil and slows the rate at which it can escape into the cold air,” explains Putnam. “This prevents the soil from getting too cold and freezing too deep, which is crucial for the tender feeder roots near the surface.”
Southern temperatures in winter can go from freezing at night to warm and sunny in the afternoon, he says. “This up-and-down causes the soil to expand and contract repeatedly, which can literally push plants right out of the ground,” Sons says. Mulch keeps soil temperatures consistent and can prevent plants from being uprooted.
Protects Roots
Plant and tree roots are insulated and protected with mulch. Soil temperatures are maintained, preventing fluctuations. “The mulch layer will keep the root layer warm, which can help keep a plant alive during colder days or during frost events,” says Guiliano.
Temperature changes can affect the soil so applying mulch provides a barrier as a form of protection. “When the air temperature drops to freezing, the mulch prevents that freezing cold from penetrating the soil and damaging the roots,” says Putnam. Snow that falls over mulch may seem problematic for its freezing temperature, but snow can act as a buffer or another layer of protection for the roots. “Snow itself is an excellent insulator because it’s mostly air, so it just adds to the protection the mulch is already providing for the soil underneath,” says Putnam.
Protects Bare Soil
If you have exposed soil, mulch can serve as a protective layer. “Winter rains can wash away bare soil, taking all that valuable topsoil and nutrients with it,” says Putnam. “Mulch acts like protective armor, holding the soil in place.”
Provides Nutrients for the Soil
Organic mulch, such as shredded bark or pine straw, breaks down slowly, putting back nutrients into the soil. “[Organic mulch] feeds the beneficial microbes and fungi in the soil, giving your plants a head start on a great growing season,” says Putnam.
Reduces Evaporation
Mulch not only helps maintain the soil temperature, it also reduces moisture evaporating from the soil. “Winter winds and dry air can pull moisture right out of the soil,” says Putnam. Mulch serves as a barrier reducing evaporation and maintaining water the roots can use, he adds.
Suppresses Weeds
Mulch also minimizes weeds, or unwanted plants, from cropping up in your garden and competing for the same resources. “Weeds don’t just stop in the winter,” says Putnam. A lot of winter annual weeds will try to come up, especially in milder Southern climates, he adds.
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