Mulching the garden for winter

One of the last gardening chores is to spread mulch around your perennials to help them through the winter.

Justin Hancock is a horticulturist with Costa Farms. He says the biggest misconception about mulch is that it’s meant to keep plants warm. The cycle of freezing and thawing is hard on shrubs and perennials, so mulch should be put down after the soil starts to freeze. 

"If you think about the way that water works, when it freezes it expands. And if you think about that around the plant roots, that constant freezing and thawing can push plants up out of the ground and expose them to cold damage," says Hancock. "But, if you wait until the soil freezes and then you lay down your mulch, you’re going to keep it nice and cold during those winter thaws, and you’re not going to see nearly as much cold damage."

How deep you mulch depends on where you live, what you’re growing, and what your pests are. For example, if you have problems with voles and rodents, don’t pile mulch too deep or you’ll be offering them a cozy nest to burrow into. Two-to-three-inches is usually sufficient.

The mulch you use should have good insulative value and air pockets. Shredded wood and pine needles are popular options. Hancock says do not use big, whole leaves.

"What can happen is that when they get wet they stick to each other and you end up with a plastering and you don’t have good aeration. So, you’re not getting a good insulative value, but then they can also eventually form a mat," he explains. "It makes it really hard for air and water to cycle through the soil the way it should, and you can run into rot or disease problems with your plants."

In the spring, remove the mulch just before the plants emerge. If you leave it on too long, the plants can suffocate as they start to grow.

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