This article has been updated from its original text.
Long before the word “mulch” entered the common gardening lexicon, American gardener Ruth Stout was praising its benefits, saying, “The unmulched garden looks to me like some naked thing, which for one reason or another would be better off with a few clothes on.”
Famous for such books as How to Have a Green Thumb Without an Aching Back and Gardening Without Work, Stout advocated a no-till, no-weed, low-water method of gardening, which she sustained for more than 45 years using mulch, and lots of it.
Today most gardeners understand that mulch benefits the vegetable patch in the following ways:
- Helps reduce water loss. When placed directly on the soil surface, mulch keeps the top few inches, where most root activity occurs, moist and cool for plants otherwise stressed by hot temperatures.
- Protects crop during heat waves. If you need to protect your garden during a heat wave, mulching will help cool soil temperatures by conserving and keeping plant roots moist.
- Hinders weeds. If applied thickly enough, mulch can eliminate weeds completely. Mulch both smothers seeds that would otherwise germinate and prevents new seeds from reaching exposed soil.
- Fertilizes your garden. Mulch adds nutrient-rich organic matter to the soil over time, creating a well-structured loam perfect for growing vegetables.
Despite the many benefits of mulching, many gardeners don’t use enough. Read on to find out how much of different types of mulch will do your garden the most good.
Best mulching materials
Straw is the golden yellow stalk of cereal grains cut from the fields after crops like barley, wheat and oats have been harvested. Most often used for animal bedding, straw is light in weight, fluffy in texture, hollow-stemmed and highly insulating, making it an excellent winter mulch for crops that stay in the ground past the last frost date.
Because it is primarily a waste material with the seeds removed, straw is also less likely to sprout when used in the garden as mulch. Despite this claim to fame, however, some straw invariably comes alive after a few rainy days. Mulching with a thick layer (4-6 inches or more) usually means the sprouting is short-lived. Another way to eliminate sprouting is to first use the straw as animal bedding for waterfowl (primarily ducks) who like nothing better than to pick out all the seeds (and bugs) for breakfast.
If you live in a moist climate where slugs proliferate, beware of adding straw mulch too early in the season, when rainy weather turns straw into a perfect slug habitat. Mulching after the weather warms and the soil begins to dry out usually addresses this problem.
Unlike straw, hay is a crop in its own right, grown for feeding animals through the winter. Cut green and dried before bailing, hay refers to any number of cultivated grasses and legumes, and may include clover and other flowers. Many gardeners avoid mulching with hay because its seed content is often high. However, this depends on your source—when was the hay cut and what plants did it contain? Is it pure alfalfa or a blend of grasses?
Hay is worth using as mulch for several reasons. Hay has a higher nutrient content than straw and will rot more quickly, adding nitrogen and other essential nutrients to your garden. Mulches that rot quickly also have a matting effect that inhibit weed growth from below. Additionally, composted hay builds optimal soil structure, creating a spongy, loamy texture favored by vegetables—and Ruth Stout, who used a mix of spoiled hay and dried leaves for decades in her Connecticut garden, with excellent results.
To safeguard against sprouting, mulch with hay when the bail has been spoiled or is too old to use for feed purposes. This means the seeds are usually no longer viable and will sprout at a much lower rate, if at all. You can also add hay to the bottom of your mulch layer, topping with straw or another material if you are concerned.
Two more practices can eliminate problems associated with hay seeds taking over your garden. First, add a thick enough layer of hay mulch (eight inches or more) to smother weed seeds and prevent them from taking hold when they do sprout. Second, don’t till or turn the soil, which disturbs your mulch layer and exposes weed seeds to the air.
If you’re like many people and have a lawn to mow, you probably have a pile of grass clippings moldering unused in your yard. Like hay, grass clippings may contain weed seeds if harvested after flowering. However, if you mow your lawn regularly and don’t treat with chemical herbicides, fungicides or fertilizers, grass clippings are an excellent source of mulch. Not only do they add important nutrients to garden soil as they break down, grass clippings also rot quickly, warming the soil as they decompose. This is a boon in the springtime when the soil is cold, but something to watch for in mid-summer when your broccoli plants prefer cool soil temperatures.
When using grass clipping for mulch on plants in mid-season, the nitrogen boost from fresh clippings can trigger a growth spurt that results in delayed flowering and fruiting for some crops like tomatoes. To reduce this possibility, let the clippings dry out and go brown before raking them up for use as mulch.
Grass clippings form a dense mat during decomposition that can choke weeds and germinating seedlings. For this reason, be careful not to cover emerging shoots with grass clippings. (They will even inhibit potatoes.) The main drawback of mulching with grass clippings is finding large enough quantities. If you have a large lawn or neighbors who want to donate to your pile, you have free mulch at your disposal.
If you are a fan of compost, you may find this method downright sacrosanct, but its results are worth considering. Adding vegetable scraps directly to your garden via a layer of mulch on the surface of the soil may not be pretty, but it is effective.
Vegetable waste adds nutrients to the soil and conserves moisture—just like any other mulch. Because it usually comes in smaller quantities, however, we add our vegetable waste over time, to the lower mulch layer. Simply lift up your hay, straw, or other mulch material and deposit your vegetable scraps directly onto the soil. By next season, the scraps will be composted and your soil will reap the benefits. You will also avoid turning and transporting your compost. Ruth Stout would be proud.
Depending on where you live, you may have ready access to a free source of mulch on nearby beaches or along the shoreline. Deposited on the beach by the tide, seaweed is an excellent source of garden mulch high in micronutrients. Seaweed is also free from weed seeds and, after a few days, it dries to a crispy mat that repels slugs.
Some gardeners may be concerned with the salt content of seaweed, but this has not been an issue in our experience. You can spread your seaweed out and rinse with fresh water, but it’s not usually necessary.
Seaweed mulch dries out within days and shrinks considerably, so you may want to reapply an additional layer to ensure there are no bare spots of soil exposed.
Bark mulch or wood shavings
Although these woody materials don’t break down fast enough for most vegetable garden beds—and can inhibit germination if blocking the soil—they do provide benefits under certain applications.
Shavings or sawdust, before or after they have been used as animal bedding, are good additions to berry beds for both inhibiting weed seeds and conserving moisture. Bark mulch can also be added to garden paths to minimize weeding and establish walkways. Cedar is best used on paths only as it is acidic and inhibits decomposition in the soil.
Be aware that woody mulches are high in carbon and will use soil nitrogen to break down. If using on or near plants that require large amounts of nitrogen, be sure to supplement with an organic nitrogen fertilizer to fully meet your plants’ needs.
If using bark mulch for garden pathways or shrub beds, ask the seller about its origins and if there have been any complaints from customers. We have used some bark mulches that contained invasive horsetail seeds, and we’re still pulling up horsetail years later.
Readily available in the fall when the changing season signals trees to shed their greenery, leaves are hard to come by in high gardening season. For this reason, spread leaves as a winter mulch to insulate your garden, increase organic matter, and prevent emerging weeds in springtime. Some leaves are more acidic than others. Depending on your source and your crop, you may need to lime the soil to compensate.
Each fall we gather and store dried maple leaves for use as a winter garden mulch and for adding to the compost through the winter months when carbon materials are hard to come by. This helps keep our winter compost balanced and less soggy. Maple leaves are low acid and, since they are large, it’s fast and easy to fill our sacks with this valued resource.
When using autumn leaves for mulching your garden beds over winter, you may need to cover them with netting or sheeting to prevent the wind from blowing them out of place.
A variety of plastic and synthetic woven mulches now exist to replicate some of the benefits of organic garden mulches. While comparable benefits include water conservation and weed inhibition, synthetic mulches do not add organic matter to the soil, improve soil structure over time, or feed soil organisms like worms and bugs. They must also be thrown away at some point in their lifespan. Additionally, using synthetic mulches may prevent the natural evolution of gardens and crop rotation if they lock the gardener into a crop-specific design.
Despite these drawbacks, synthetic mulches do have their place in some gardens. Many find that landscape fabric applied to a garden path and covered with bark mulch lessens the workload for several years running. Black plastic mulch used in strawberry or squash patches can also warm the soil early in the season, giving a jumpstart to heat-loving crops. (Be aware that a further layer of organic mulch may be needed as the weather warms to prevent plastic mulch from functioning too well and overheating the soil and your plants later in the season.)
Garden mulching tips
- Use materials you have on hand or those that are readily available from local farms or beaches.
- Apply mulch thickly to the soil surface. Depending on the materials used, this is anywhere from 4-8 inches in depth. When in doubt, add more mulch.
- Apply mulch any time of year. If applying in summer and the ground is dry, irrigate before applying. The mulch will conserve moisture in the soil and guard against evaporation. In early spring, hold off applying mulch until the soil warms and starters are established.
- Pull fresh clippings, seaweed, and other moist mulches back from plant stems during application. As mulch dries, it will shrink and retract even further.
- If you are concerned about your mulch containing weed seeds, apply thickly (at least 8 inches thick). Alternatively, expose your mulch to rain and weather before spreading, allowing any weed seeds to sprout and die before application.
A final word about mulch
Applying mulch to the garden is a simple practice that can lessen your workload and save you money over the long term. In Stout’s own words, “There is peace in the garden. Peace and results.”