Mulch is any material, synthetic or organic, spread over the ground as a covering. Mulch can be leaves, wood chips, newspaper, pebbles, or even plastic and polyester fabrics—basically, anything that stays in place and protects the soil (more on the types of mulch). The protective layer it provides keeps the soil cool and moist in the summer and insulates tender perennials in the winter.
Mulch is a champion at smothering weeds, which saves time and energy for us hardworking gardeners. In the spring, spread two to four inches of mulch on garden beds to prevent new weeds from growing near vegetables and perennials. For really overgrown areas, use damp cardboard as a barrier and cover it with a generous layer of mulch, which is usually enough to knock out even the worst weeds.
Our favorite mulching superpower is its ability to support a healthy ecosystem under your feet, which benefits your crops and the planet. Natural mulches are high in carbon, which soil organisms like microbes and fungi need to survive. These organisms feed on the mulch, breaking it down, capturing carbon, and releasing essential nutrients that plants absorb as they grow.
Plants also pull carbon out of the air to form sugars used to fuel cellular activity. Any excess sugar is released through roots to support soil organisms in exchange for access to nutrients. The alliance between plants and soil organisms locks carbon underground as humus, the dark soil that every gardener lusts over, thus lowering the amount of carbon in the atmosphere.
Mulch can be applied anytime of the year, but you’ll see the greatest benefits if you do it in mid-spring or fall.
The benefits of spring mulch
Mulching in the spring prevents weeds from growing, adds nutrients, and helps your soil retain moisture.
Garden expert Acadia Tucker’s go-to spring mulch is a 50/50 mix of shredded leaves and grass clippings because she always has a lot of yard waste. Shoveling leaves and grass onto your plant beds feeds the soil with nutrients well into the fall without having to turn over the compost pile. If you don’t have a steady supply of yard waste, consider asking your friends and family to save theirs.
Another option is to find some hay to use—old, slightly decomposed hay makes for a great spring mulch in the absence of yard waste. If all else fails, you can always buy mulch online or at your local home and garden store.
The benefits of fall mulch
Laying down a protective layer of straw before winter can prevent the pounding rain and winds from washing away fertile topsoil. Straw has the added bonus of insulating plants from the freezing cold. Mulching in the fall is like tucking in your plants to keep them safe against winter rain, sleet, and snow.
In the fall, spread a layer of wood chips over your garden paths. Coarse materials like wood chips act as a cushion to protect the soil from being packed down by winter storms. You don’t want compacted, poorly aerated soil because it’s unable to absorb rainwater, hold nutrients, and support healthy microbial activity and root development.
Weed before mulching
Before spreading your first layer of mulch, take the time to thoroughly weed your garden beds. Mulch is effective at discouraging weed growth, but it can’t do much to kill weeds that are already well established. This task might seem daunting but think of it this way—after a few seasons of mulching, there won't be any more weeds to pull.
You can also lay down a black plastic tarp over the ground you want to clear, and secure it with stakes. The dark plastic warms the soil so intensely that it kills living weeds and weed seeds on the soil surface. This method also allows you to avoid disturbing the soil. Before you lay down the plastic, which you can buy from any online farm or garden store, rake compost into the first inch of soil. If you have plants growing in the bed, simply put the compost on top of the plants. If it’s the late fall, winter, or early spring you'll need to wait six to 10 weeks before removing the plastic. If it's warm outside, late spring through early fall, two to six weeks should be enough time to suffocate the weeds.
A third option is to use so-called lasagna gardening or mulching, where you layer cardboard, seaweed, leaves, grass, and repeat. We prefer this option because it not only kills weeds but builds soil.
Prep the soil before mulching
Mix compost into the first few inches of your soil to add nutrients and encourage your plants to grow strong and healthy. Then soak the ground. After the first good soak, the soil stays damp longer, sharply reducing the amount of water you’ll need for the rest of the summer. In arid climates, mulching in the spring is the single best thing you can do for your plants.
Another good reason to soak your soil is because organic mulches absorb a lot of water and end up stealing it from plants if there’s not enough to go around.
Spread the mulch
Load a wheelbarrow or garden cart with your favorite mulch (learn how to choose your mulch here). Scoop mounds of it onto your garden bed every few feet. Use a rake to smooth out the piles. What you want is an even layer of mulch, two to four inches thick. Don’t overdo it! Spreading too much mulch makes it hard for rain to hydrate the soil.
You also don’t want to mulch too closely to the root crowns and stems of your plants, or you may produce rot. Aim for a distance of two inches. For larger perennials and trees, keep mulch at least eight inches from their base. In the spring, push mulch away from the base of perennials to prevent decay and give plants a head start into the new growing season.
One problem with mulch: It can attract pests. Rodents love its insulating powers and burrow into it to stay cozy during cold snaps. Mulch also hides slugs and snails that gnaw on vulnerable leaves in the coolness of night. If you have trouble with pests, avoid putting thick layers of mulch down in the fall.
Consider spreading a layer of coarse wood chips over garden paths each fall; the coarse material acts as a cushion to protect the soil from being packed down.