Whenever I can simplify a chore and maximize the results, I’m on board — especially in the garden. I’ve found that one of the best ways of accomplishing that is to cover the ground with a blanket of mulch. Not only is it one of the easiest and quickest garden chores to take care of, its impact is far-reaching and at times can be the reason a plant thrives.
Simply defined, mulch is a layer of material applied to the soil surface. Mulches are typically organic in nature and often consist of compost, aged manure, grass clippings, bark mulch, wood chips, straw or shredded leaves. Leaves left whole can form a thick mat and inhibit the infiltration of water, air and nutrients. The material doesn’t have to be organic, however, to be utilized as mulch. Inorganic materials like plastic sheeting, geotextiles and landscape fabrics, and rocks and gravel are classic examples.
The main difference is that organic mulch materials will eventually settle and decompose, adding organic matter and nutrients to improve the productivity of the soil. When the soil is more productive, so are the plants whose roots live in it.
Organic materials, though, are temporary and need to be reapplied, whereas inorganic mulch materials are much more permanent in nature. Inorganic materials can be difficult to remove, especially in the case of rocks, gravel or plastic sheeting, which eventually breaks apart. These materials are therefore best suited to certain permanent plantings or the seasonal vegetable bed.
While there is no ideal mulch for every situation, there are desirable attributes to look for in most cases: Quality mulch allows water and air into the soil, resists compaction, is odor-free and attractive, and stays in place. Ultimately, though, the best mulch is one that you can easily and cheaply access and apply to your garden.
You often can find straw, bark dust or wood chips at farming centers, feed stores, home improvement stores, garden centers, or in the ad section of your local paper. Of course you’re already one step ahead if you have a chipper, as you can make your own wood chips and sawdust from tree and shrub trimmings. You also may already have compost, shredded leaves, grass clippings, pine needles, newspapers, ground corn cobs or even coffee grounds, which can even help repel and kill slugs. Materials such as nut or rice hulls, animal manure, aged sawdust or vineyard waste can also be purchased as by-products from a local company or winery.
When choosing a mulch material, keep in mind that some may be less aesthetic and more of a challenge to put in place than others. Big rocks and 75- or 100-pound straw bales are heavy to move, plastic tears and shreds over time, and straw may not beautify your perennial bed. Yet in the right setting, each of these makes excellent mulch.
The benefits of mulch are multifold: It suppresses weeds, moderates soil temperatures, conserves soil moisture, increases the population of earthworms and beneficial soil microbes, and improves soil texture and soil fertility. To reap the most benefits from your wood chips or other material, there are a few things to keep in mind.
For starters, mulch does not prevent all weeds, but it does greatly reduce their numbers. This works by keeping light from reaching seeds or weeds. The more tenacious weed seeds may still germinate, and particularly tough weeds will still push through most any mulch — even landscape fabric. But the weeds are fewer and far between, and those that do appear are usually much easier to pull.
Mulch moderates soil temperatures by acting as a blanket of insulation, which shades the soil to keep it cooler when above-ground temperatures are warm and helps keep it warmer in cold weather. The more moderate underground temperature makes for a more hospitable environment for earthworms and beneficial soil critters. And this blanket of insulation also conserves soil moisture by slowing evaporation by 10 to 25 percent, and perhaps more in some settings. That way you save time and energy by watering less often while your plants are none the wiser.
Whether you rake it, dump it, have it blown in or spread it with your hands, the amount of mulch needed depends on the type of material that you’re using and where you’re using it. The thickness can vary from 1 to 4 inches or more; the finer and denser the mulch, the less you need to apply. Maintain a 1- to 3-inch layer for fine-textured materials — such as sawdust, shredded leaves and compost. Coarse-textured materials — like wood chips, straw, or pine boughs and other evergreen branches — are best kept at around 4-inches thick.
Organic mulch will eventually settle as earthworms and soil microbes decompose the material. Some decompose faster than others, though, so you’ll need to keep an eye out for when additional mulch is required.
When it comes to choosing and using the ideal mulch, timing is everything. Mulch applied at the wrong time in spring may actually slow the growth of certain plants. If it’s applied at the wrong time in winter, mice may overwinter in the mulch and munch on bark or plant roots. Likewise, some materials serve better in one season as opposed to another.
Mulch applied in early spring will prevent many weed seeds from germinating. Mulch applied in late spring will keep soil cool and conserve moisture as the warmer days of summer approach. Keep spring mulch on the lean side, with shallow 1- to 2-inch layers.
Spring mulch is best for pansies and permanent plantings, such as trees and shrubs. But when it comes to the flower garden or vegetable garden, it’s best to wait until after the soil has warmed (late spring or early summer, depending on your area). Otherwise, the cool, wet soil may delay spring growth or slow germination of seeds.
Ideal mulches for spring plantings, beds and borders include seaweeds, spent hops, grass clippings, spent mushroom substrate, compost, or aged manure — all of which improve soil fertility, thereby giving plants a much needed nutrient boost in spring.
Landscape fabrics used around trees and shrubs or on pathways between beds can be used as base mulch and then topped with a thin layer of more attractive mulch, such as wood chips or nut hulls. The two together will provide more protection against weeds than either one alone. Wet newspapers also can be layered in pathways or around new plantings and then covered with a top mulch.
Mulch applied in early summer is probably the best defense against the season’s heat, for it helps keep soil cool and retain soil moisture. And like in spring, summer mulch also will reduce weeds.
If you haven’t already done so, now is the time to address your vegetable or flowers beds. Use pine needles as mulch for blueberries, hydrangeas and other acid-loving plants. Save your hostas and other slug-prone plants by applying coffee grounds. Or add another layer of compost or aged manure to give growing plants the nutrient boost they need. Straw mulch in the summer kitchen garden will help keep fruit and vegetables from rotting by keeping them off the ground. This is especially important when soil is high in organic matter, since the healthy population of earthworms will eat away at any produce in contact with the soil.
Early summer is the perfect time to put plastic mulches in place. The type will depend on your needs. For example, black plastic suppresses weeds and warms up the soil by a few degrees — a difference that northern gardeners or gardeners in cooler climates need to make warm season vegetables more productive. Clear plastic increases soil temperatures even more — by 8 to 14 degrees — but it is not as good at weed suppression. White plastic keeps soil temperatures cooler — a benefit for southern gardeners or those trying to extend the season for cooler-season crops. If your garden is in the South and subject to high temperatures earlier in the season, spring would be the ideal time to apply plastic mulch since warm season transplants are put out earlier.
Infrared Transmitting (IRT) plastic generally comes in two colors, brown or green — although not all brown and green mulch is IRT — and is a relatively new invention that warms the soil on par with clear plastic yet allows for greater weed suppression as with black. In addition to these properties, green IRT mulch is great for cantaloupes as it encourages earlier ripening and greater yields.
Reflective silver mulch reduces the numbers of certain pests, including aphids, whiteflies and cucumber beetles. Red plastic increases yields and plant size of tomatoes, eggplant, peppers, okra, strawberries and basil by up to 20 percent more than black mulch. And dark blue plastic mulch increases fruit yields in cucumbers, summer squash and cantaloupes.
Even though mulch has served its purpose during the height of the gardening season, it doesn’t end with the arrival of autumn. Mulch applied in the fall helps keep the soil warmer longer, thereby extending the flowering season for some perennials and annuals and the harvest season for certain vegetables and herbs. It also continues to conserve soil moisture and restrain weed growth.
In the fall, mulch annual beds before the first frost settles in. Roses will benefit from a thick layer of mulch applied in mid to late fall. Protect the roots of trees, shrubs and perennials from hard freezes with a thick layer of mulch around the base.
Mulches of shredded leaves, garden debris, grass clippings and compost will also provide food for earthworms, microbes and other beneficial creatures that live in the soil. Even woody organic material, such as straw, pine needles, nut hulls and bark chips, provide food for carbon-eating fungi and microorganisms that break down the material, improving soil structure and delivering valuable nutrients to plants for the gardening season ahead.
The main benefit of winter mulch is to protect plant roots from the onslaught of heavy freezes and temperature extremes. In unmulched soil, temperature fluctuations create movement that can cause many small or shallow-rooted plants to be heaved out of the soil, thereby exposing their crowns and upper root systems to damaging freezes. An insulating blanket of winter mulch, however, provides a protective barrier between the soil and the air. This seasonal mulch is typically removed at the end of winter and composted.
The best mulch materials for winter include straw, hay, pine or evergreen boughs and other fibrous organic materials. Loose materials such as these protect plants and insulate the soil without compacting under the weight of snow or ice.
Shredded leaves and compost provide good winter cover for perennials and bulbs, which can easily push through the mulch come spring. Pine needles function best as winter cover for ornamental beds and shrubs. Straw is an inexpensive, lightweight insulator and winter cover for vegetable and strawberry beds — uncover strawberry plants when growth begins in spring. And bark chips work well around trees and shrubs.
It’s best to wait until after the first hard or killing frost before applying winter mulch. Doing so will deter mice as they will have already secured a warm site elsewhere in which to take cover and overwinter.
Simplify the process of protecting, enriching and maintaining the health of your soil by making mulch the multitasker for your yard and garden. This one-step process can be so simple yet so significant to a beautiful garden and thriving landscape.
• The best time to apply mulch is when the soil is moist, just after you water or it rains.
• Keep organic mulch in place when applying fertilizer since nutrients will travel through the mulch and down to the roots when watered.
• Avoid using sprayed grass clippings and treated wood materials.
• Remove weeds before applying mulch. A thick layer of wet newspapers or landscape fabric topped with mulch is the exception.
• Keep a mulch-free zone around plants, trees and shrubs: Leave about 1 to 2 inches of space for plants; a 4- to 6-inch space around shrubs; and allow for a 12- to 24-inch circle around the base of trees.
Kris Wetherbee lives in Oakland, Oregon, where she mulches her vegetables with compost, straw or wood shavings in late summer and fall.
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