Mulching is a common gardening practice with many benefits. But using mulch incorrectly can have the opposite effect. Here’s how to mulch a garden—and get the most out of mulching.
What is Mulch?
At its simplest, mulch is a material that covers the soil for variety of reasons, usually controlling weeds.
Advantages of Mulching
Mulch has been called the gardener’s friend—and for good reason. It offers three major benefits:
- Suppression of weeds
- Conservation of moisture in the soil
- Moderation of soil temperatures, keeping it warmer on cold nights and cooler on hot days
There are also many other benefits of mulch:
- In winter, protect plants from the cycle of freezing and thawing (which can heave them out of the ground)
- Prevent soil compaction and crusting
- Slow down runoff and erosion, especially on slopes
- Break down and feed the soil (if organic mulch such as grass clippings)
- Warm the soil in spring, allowing the gardener to plant days or weeks before the soil would normally be ready
- Keeping plants off the ground, especially tomatoes and melons, to avoid plant disease
- Keep plants clean, especially lettuce and celery, preventing rain from splashing soil that could carry disease onto plants
- Making gardens “spiffed up” and attractive
Disadvantages of Mulching
Although using mulch has many benefits, it can also be detrimental to the garden in mainly two ways:
- Overmulching can bury and suffocate plants
- Mulch provides a convenient hiding place for pests
- Bake your plans with excess heat if done incorrectly.
With most organic mulches, a layer of 2 to 4 inches is plenty. The finer the material, the thinner the layer needed.
Unfortunately, mulch provides the perfect place for slugs, snails, and other pests to hide. Use shallow cups of beer to attract and drown them, or sprinkle wood ashes or diatomaceous earth around the base of precious plants to keep the slugs and snails at bay.
Impervious mulches, like black plastic, don’t let air or water in. Even matted leaves can have that same effect, so shred or chop them up first.
Light colored, wood-based mulches, like sawdust or fresh woodchips, 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.)
Dry mulches—including sawdust, woodchips, peat moss, and dry straw—can be a fire hazard. Keep them away from buildings to be on the safe side.
Types of Mulch
The ideal mulch should be dense enough to block weed growth but light and open enough to allow water and air to reach the soil. Factors to consider when purchasing mulch are cost, availability, ease of application, and what it looks like in the garden. There are lots of materials of various colors and textures to choose from.
Here are a few of the more popular mulches:
Organic mulches insulate the soil. Mulching crops that prefer a cool soil like lettuce, peas, and spinach can lengthen the harvest period or improve the harvest.
- Shredded or chipped bark. Keep it away from the base of trees and shrubs to prevent wood boring insects and decay from attacking the plants.
- Shredded leaves and leaf mold eventually break down and feed the soil with beneficial materials.
- Straw and salt marsh hay are free of weed seeds.
- Grass clippings should be dried first or spread thinly to keep them from becoming a hot, slimy, stinky mess. Don’t use clippings from grass treated with chemicals.
- Pine needles are slow to break down, so don’t worry about them adding to soil acidity.
- Local byproducts, such as spent hops from a brewery, cocoa hulls, ground corncobs, coffee grounds, newspaper, or cardboard. Get creative!
An example of improper mulching. Don’t be guilty of creating mulch volcanoes like this one around your plants!
- Plastic mulch comes in many colors for different purposes. Black plastic mulch will warm the soil more quickly in the spring and hold the warmth over night. This can make a big difference in short growing seasons. Red mulch increases fruit yield in tomatoes, while blue mulch does the same for potatoes. Silver or white mulch reflects light and heat.
- Crushed stone, gravel, marble, or brick chips provide a permanent mulch around shrubs and trees.
- Landscape fabric smothers weeds while allowing air and water to pass through.
To cut down on weeding in our vegetable garden, we use a permeable landscape fabric on many of the beds.
After a few spring rains, we lay down soaker hoses in each bed and cover them with the fabric.
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 straw, grass clippings, and shredded leaves for crops that like it cooler.
If you have problems with weeds or plant dehydration, follow the above advice and try mulching in your own garden! For more on mulching, read about mulching to control weeds and save water, and check out our guide to composting.