How to Mulch Your Garden | Types of Mulch

Mulch has been called the gardener’s friend—and for good reason. 

• In the spring, mulch retains moisture, suppresses weeds, and prevents erosion. 
• In the fall, wait until after the first hard frost and mulch to prepare plants for the winter, protecting bare soil from freeze-thaw patterns and insulating the plant roots.

What Is Mulch?

At its simplest, mulch is any material that covers the soil’s surface. In nature, mulch is simply fallen leaves and plant debris. In the garden, mulch can also include compost, wood chips, rotted manure, cardboard, or even seaweed.

It’s only recently that we’ve come to appreciate mulch’s sustainable and ecological benefits. Done correctly, mulching feeds our soil’s living microorganisms with nutrients, and the waste from these tiny microbes creates a healthier soil structure for plants, limiting compaction.

The Benefits of Mulching: Why Should I Mulch?

1. Reduces weed growth by keeping light from reaching the soil surface.
2. Reduces water loss from the soil surface, which helps maintain soil moisture.
3. Moderates soil temperatures, keeping soil warmer on cold nights and cooler on hot days.
4. Protects bare soil, reducing erosion and soil compaction.
5. Protects plants from the harsh conditions of winter freezes, thaws, and winds.

There are many other benefits of mulch:

• In winter, the soil under the mulch will be warmer than unprotected soil. This protects plants from the cycle of freezing and thawing (which can heave them out of the ground).
• Prevents crusting of the soil surface. Water moves more readily into soil covered with mulch instead of running off.
• Keeps soil from splashing onto leaves; keeping soil off leaves reduces the chance of plants contracting fungal and bacterial diseases.
• Breaks down and feeds the soil (if organic mulch).
• Improves the structure of clay soils and the moisture-holding capacity of sandy soils.
• Slowly increases soil fertility (if organic) and may make micronutrients already in the soil more available.
• Warms the soil in spring, allowing the gardener to plant days or weeks before the soil would normally be ready.
• Keeps plants clean and off the ground, especially tomatoes and melons, to avoid plant disease.
• Limits the chance of damage to tree trunks when mulch is placed around them instead of grass.
• Improves plant health and growth (due to fewer weeds and more consistent moisture and soil temperature).
• Makes gardens “spiffed up” and attractive, giving a uniform appearance and rhythm to garden design.

Disadvantages of Mulching

Although using mulch has many benefits, in some cases, its use can be detrimental to the garden:

• Do not over-mulch. Aim to apply a 2- to 3-inch–thick mulch layer. More than that amount will bury and suffocate plants; water and oxygen can’t reach the roots.
• Don’t layer mulch deeply over perennial plant crowns (the growing points).
• Don’t pile up mulch near the trunks of trees and shrubs. Keep mulch 6 to 12 inches away from the base of woody plants to avoid rot, wood-boring insects, gnawing rodents, and decay. 
• If you have perennial gardens, don’t apply fall mulch too early. Wait until after the first hard freeze after you cut down perennials; be sure to leave some perennial stems for native insects. 
• Light-colored, wood-based mulches, like sawdust or fresh wood chips, can steal nitrogen from the soil as they break down. Counter this effect by adding a nitrogen-rich fertilizer, such as soybean meal, alfalfa, or cottonseed meal, to the mulch. (Learn more about soil amendments.)

How Much Mulch Do I Need?

With most organic mulches, a layer of 2 to 3 inches is plenty. The finer the material, the thinner the layer needed.

Inorganic mulch is often more shallow. For example, a mulch of small stones usually only needs to be an inch deep.

1 cubic yard = 27 cubic feet

Types of Mulch 

The ideal mulch needs to trap air to provide insulation and warmth, similar to down in a winter coat. It needs to be dense enough to block weed growth but light enough to allow water to reach the soil. Both organic and inorganic mulches can be used effectively in the garden. 

Organic Mulches

Organic mulches are natural products from leaves, trees, grass, and other plant material, often from your own yard. They mimic nature, breaking down gradually over time. The advantage is that they are truly adding organic matter to the soil. The disadvantage is that they must be replenished periodically. 

1. Shredded bark. Softwood bark mulch is attractive, resists compaction, and breaks down slowly. Hardwood bark is attractive but breaks down quickly and needs to be properly composted to avoid sour mulch and nuisance fungi.
2. Shredded leaves are readily available and, if chopped, eventually break down and feed the soil with beneficial materials. The disadvantage is that leaves can mat if wet, which reduces the oxygen and moisture in the soil. Avoid matted layers of wet leaves.
3. Weed-free straw and salt marsh hay are inexpensive and helpful coverings; however, they decompose more quickly, may harbor rodents, and are easily blown away by the wind.
4. Pine and cypress needles are attractive and stay in place better than most mulches. They are slow to break down and aren’t as acidic as you might expect, so don’t worry about them changing the soil’s pH.
5. Local byproducts, such as spent hops from a brewery, cocoa hulls, ground corncobs, coffee grounds, newspaper, or cardboard can also be mulch. Get creative!

Inorganic Mulches

• Black plastic mulch helps warm the soil in spring, reduces water loss, and is convenient. This can make a big difference in short growing seasons. However, it’s not permeable, so it’s more difficult to water; it also breaks down when exposed to sunlight, and the soil under the plastic becomes very hot in the middle of summer if not shaded by leaves or covered with another mulch.
• Silver plastic mulch excels at warming soil in spring but doesn’t control weeds; the soil becomes even hotter with clear plastic in midsummer, and plants can be damaged if the plastic is not shaded.
• Crushed stone, gravel, marble, or brick chips provide permanent mulch around shrubs and trees. That said, these mulches are expensive, hard to move, and can get into the lawn. Weed seeds and soil can still find their way into the stones; an underlayer of landscape fabric will help prevent this.
• Landscape fabric smothers weeds while allowing air, fertilizer, and water to move through it and into the soil. It is treated to resist decomposition and helps retain soil moisture. It’s important to fasten the fabric down so perennial weeds do not push it up.

How to Apply Mulch

Mulching in Spring

Remove winter mulch in the spring when the danger of a hard frost is past so that the ground can warm and new growth will not be inhibited.

If there are many weeds on the ground where you want to grow, consider installing permeable landscape fabric on many of the beds.

Or, lay down a layer of cardboard before adding your organic matter. Thoroughly wet the cardboard to help it break down. The cardboard will serve as a further barrier to weeds, exhausting and eventually killing most of them. Once the growing season gets underway, you’ll find that any weeds that do manage to make it through will be much easier to remove.

After a few spring rains, when the soil has warmed, we lay down soaker hoses in each bed.

Then, we cover the hoses with a fabric to speed up the change in soil temperatures and warm the soil for earlier planting.

Planting holes are cut at different spacings for different crops. Watering is efficient, and maintenance of a large area is made much easier.

Once the plants get some size on them, the fabric is covered and does not look so bad! We also use organic mulch, including straw, leaf mold, grass clippings, wood chips, and shredded leaves for crops that are cooler.

Regularly mulch with organic matter. Replace old mulch as it rots down or becomes incorporated into the soil so that the ground is constantly fed and gradually built up. 

Mulching in Autumn

Don’t mulch too early in the fall, except for in bare, unplanted garden beds to prevent erosion. The soil will not cool down quickly, and plants may continue to grow. New growth may not harden off and can be damaged by winter cold. Also, mulching in the fall keeps the soil wet, which can lead to root rot and plant death.

But once you’ve had several freezes (often around Thanksgiving or after), mulch! The ground needs to be cold and hard. The mulch will help the soil cool down slowly, preparing plants for winter. It will also save you time in the spring. Shredded mulch, straw, pine needles, or shredded leaves are all good winter mulch. Apply 3 to 4 inches. It’s important to apply enough mulch in winter to keep the frozen ground completely covered so the plant remains dormant until spring no matter what type of warm or cold spells occur.

Apply mulch around the base of any tender perennial plants or new plants. Grafted plants, like hybrid tea roses, benefit from being mulched heavily. Take care NOT to put mulch next to the trunks of trees or crowns of plants, as this invites bark-gnawing rodents.

In bare areas, cover with mulch unless you are planting a winter cover crop (which you’ll till under in the spring). Spread a thick layer of soil-conditioning compost or well-rotted organic matter over the bare soil. You could also use shredded leaves. Lay it at least 4 inches deep. Fast forward a few months, and any grass and weeds below will have rotted down, while earthworms will work to gradually incorporate the organic matter into the soil below.

Protect the branches and buds of evergreen or semi-evergreen shrubs, such as rhododendrons and viburnums, by wrapping them with burlap or using a tree guard filled with shredded leaves for insulation.

Check out our guide to composting!

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