How to Mulch for the Healthiest Yard and Garden

What's the Purpose of Mulch?

Mulch is a protective layer of organic or inorganic material that’s applied to soil to conserve moisture, suppress weeds and enhance soil fertility.

Here are several ways mulch works in your landscaping:

• Keeps the weeds down and makes them easier to remove
• Slows evaporation of water, saving time on watering your plants and money, too
• Insulates the soil, protecting plants from extreme temperatures
• Gives beds a finished, polished look

Organic vs. Inorganic Mulch and When to Use Each

Derived from natural materials, organic mulch decomposes over time, enriching the soil. Common examples include bark, straw and grass clippings. Bark mulch, often sourced from shredded tree bark, not only can enhance the natural beauty of your garden, but also retain moisture and suppresses weeds. Straw is ideal for vegetable gardens, providing insulation and preventing erosion. Grass clippings, readily available after mowing, offer a quick and effective means to recycle yard waste while enriching soil fertility.

Here's a tip from The Morton Arboretum in Illinois: Organic mulch should be composted or otherwise treated before use. The step kills insects, weed seeds and disease microorganisms. The texture of composted mulch generally is more uniform, which also means better curb appeal.

Inorganic mulch consists of durable, non-biodegradable materials like stones and landscape fabric. Stones such as gravel or river rock provide long-lasting coverage that's often used for decorative purposes. Landscape fabric is often used underneath stones or shredded hardwood bark to extend its lifespan.

When to Apply Mulch

In spring, mulch retains moisture and suppresses weeds as temperatures rise and plants begin to grow. Summer mulching protects plants from extreme heat, stabilizing soil temperatures and preventing evaporation.

Fall mulching prepares your garden for winter, safeguarding plant roots and enriching the soil as organic matter breaks down. Wait until after a hard frost in the fall to apply winter mulch. You don't want to apply it too early in the fall because mulch can delay the soil freezing process by retaining heat in the soil, according to experts with The Morton Arboretum.

Reasons to Practice Fall Mulching

• Mulch in fall to skip that job come spring. Every gardener knows spring is a busy time, and late fall typically offers a leaner to-do list of garden chores. Fall mulching frees up time next spring.
• Cut back perennials for winter, and you create a clean bed surface that makes mulching a snap. There's no dodging emerging bulbs, perennial shoots or seedlings. The bonus is that cutting perennial stems down in fall takes that chore off your spring to-do list.

Reasons to Skip Fall Mulching

• For best mulching results, you need to cut back perennial stems to 6- to 12-inch stubs so you can apply mulch evenly around them. Fall mulching isn't for you if you like to leave perennial stems to provide winter interest and insect or bird shelter.
• If self-sowers play a large role in your plantings, skip fall mulching. That fresh layer could interfere with seed germination in spring.
• In regions where the snow starts flying early, you run the risk of having a snow-covered mulch pile if you don't get it all put out before winter arrives.

How to Apply Mulch: Step-by-Step Guide

1. Target the Mulching Areas

Spread mulch under trees, shrubs and throughout planting beds, as seen at this home by OakBridge Timber Framing on 5 acres on Lake Erie, Ohio.

2. Prepare the Garden Bed

Remove debris, weeds and old mulch. Use a garden fork or hoe to loosen the soil and consider adding compost to boost the soil fertility.

3. Figure out How Much Mulch You Need

If you're wondering, “how much mulch do I need?”, calculate the area you wish to cover and the desired depth. Typically, a cubic yard of mulch covers about 100 square feet at a 3-inch depth.

4. Apply Your Chosen Mulch

Thickness

Spread the mulch across the soil surface. The recommended mulch depth is 3 to 4 inches for medium- to coarse-textured materials, say experts with The Morton Arboretum. If you’re gardening in slow-draining soil, use a thinner layer (1 to 2 inches); for fast-draining soils like sand, aim for 4 inches. A too-thick layer can lead to plant rot, diseases, pests and rodents.

Placement

Keep mulch away from the base of a tree, creating a donut-hole affect, advises The Morton Arboretum. The mulched area should extend to the drip line of the tree branches, or at least cover a 4-5 foot diameter area around the trunk. Avoid volcano mulching, which is created when mulch is piled up around the trunk. When mulch is placed right next to the tree base, you can see the ill effects on the trunk, says Josh Fuder, agriculture and natural resources agent for UGA Extension-Cherokee County. Too much moisture will gather around the base, and the bark can decay.

Water

Water mulch after application. This keeps dry mulch from absorbing soil moisture (and stealing it from plant roots). Second, it helps anchor lightweight mulches easily carried by wind.

5. Maintain the Mulch

Maintain your garden bed by regularly checking the mulch for compaction or decomposition, replenishing as needed to preserve the right depth. During dry spells, monitor soil moisture levels under the mulch.

What to Mulch

Perennials and Annuals

A two-inch layer of mulch can keep perennials and flowering annuals content during the growing season. As it decomposes, you may need to add another inch or so to replenish the bed.

Roses

These beauties need plenty of water, so a thick blanket of mulch – three to four inches – will help retain moisture in the soil. Make sure the mulch is not piled up around the base of the plant.

Bulbs and Tubers

It’s not necessary to mulch bulb beds at planting time. If mulch is used, the depth of the mulch should be figured in to the planting depth of the bulb. Tubers that are planted in a shallow bed, such as bearded irises, should not be covered with heavy mulch.

Vegetables

A layer of pine straw, wheat straw or grass clippings or compost between the rows in your raised or in-ground beds can discourage the unwanted weeds that compete with your produce for water and nutrients.

Trees and Shrubs

When you plant new trees or shrubs, a deep layer of mulch can help get these larger landscape features off to a good start. To mulch a newly-planted tree or shrub, place a two- to four-inch layer of mulch around the tree out to the tree’s drip line, then use a rake to pull the mulch away from the trunk so that you can see the root flare, the point where the tree trunk meets the roots. This creates a “saucer” around the tree that helps direct water to the tree’s roots.

Mulching Do's and Don'ts

1. Do Use Mulch as an Accent

Mulching can help create healthy lawns but also has an aesthetic value. Choose colored mulch that complements the exterior colors of your home in the brick, stone, stucco and siding. For example, brownish/red pine mulch goes well with brick houses, says Jeremy Becker, owner of FireFly Landscapes in Kansas City. Using a dark mulch can contrast with flowers, improving your landscape design. Mulch also can be used to enhance your landscape theme and setting.

2. Do Look at Your Entire Landscape

Some landscapes have big expanses of mulch with a few shrubs poking around, says Susan D. Day, an associate professor in the Department of Forest Resources & Conservation and Department of Horticulture at Virginia Tech. “You want to design your landscapes so your shrubs cover all of the soil and you have complete vegetative cover. Then apply mulch to them, to control moisture,” she says.

3. Don’t Ignore Bare Soil

Researchers are finding mulching has significant environmental benefits. Having bare soil on your property will cause erosion and sediment runoff, Day says. Mulching can help control erosion. Research by Day and Virginia Tech graduate student David Mitchell found that bare soil lost about five times as much sediment as soils covered with mulch.

4. Don’t Assume You Need Something Underneath

Some people may want to use plastic or geotextiles, such as landscape fabric, to separate certain mulches, such as inorganic stone mulch, from the soil, Day says. There’s a belief that black plastic will keep weeds down. But adding a layer of plastic or landscape fabric could cause more water runoff and keep your garden from having a clean, streamlined look.

If you use an organic mulch that will break down, like shredded hardwood bark, avoid landscape fabric because you want the mulch to be in contact with the soil to improve it, Day says. Plastic or landscape fabric could prevent water and rain from reaching the soil, and actually could increase runoff. Weeds also could grow into the landscape fabric, she adds.

If the mulch shifts around or is replaced, the plastic or landscape fabric could show through. “It looks hideous when you have plastic or landscape fabric being exposed under the mulch,” Day says.

5. Don’t Use Bad Mulch

The biggest pitfall is getting your mulch from an unreliable source, Day says. For example, mulch could be delivered with noxious weed seeds in it because it was stockpiled next to a field of weeds. "You could be paying for that for a long time," she says.