How Much Mulch Do You Need?

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A guide to using mulch for your garden

When it comes to getting top garden or farm results, mulch makes a difference. Agreement on that score is just about unanimous, particularly among followers of the organic method. The value of a layer of material placed on the soil surface is pretty well recognized today by gardeners of all shapes, sizes and sections of the country. Most of them, for example, are keenly aware that mulching is a boon to the busy or part-time gardener; that it eliminates weeding, hoeing and cultivating, or considerably cuts these chores to a pleasant minimum; and that it holds vital moisture effectively, making irrigation and extra watering necessary far less often. Then, too, most of us know that a natural mulch benefits plants in other ways — helping to maintain an even soil temperature in weather extremes, simplifying the planting and harvesting steps, and contributing an important enrichment of the soil as it decomposes and adds humus and minerals to the topsoil.



The catch — if really there is one — lies in deciding on the amount of mulch to use. Should a good mulch always be the same depth? Must it be measured to slide-rule accuracy to function right? Do any other considerations influence the proper quantity? In other words, how much mulch is enough?

Generally, gardeners mulch crops that are in -the garden for most of the summer. How much? During the growing season, the thickness of the mulch should be sufficient to prevent the growth of weeds. A thin layer of finely shredded plant materials is more effective than unshredded loose material. For example, a 4- to 6-inch layer of sawdust will hold down weeds as well as 8 or more inches of hay, straw or a similar loose, “open” material. So will one or two inches of buckwheat or cocoa bean hulls, or a two- to 4-inch depth of pine needles.

Leaves and corn stalks should W shredded or mixed with a light material like straw to prevent packing into a soggy mass. In a mixture, unshredded leaves can be spread 8 to 12 inches deep for the winter. To offset the nitrogen shortage in sawdust and other low-nitrogen materials, add some compost, soybean or cottonseed meal.

Ground corncobs are a highly recommended mulch. Light and bulky, they help to “fluff up” the soil, thus preventing crust formation. A ground cob mulch helps to prevent blank spot on roses. Peat moss, although it doesn’t contain amy nutrients, improves soil, aeration and drainage, ultimately helping plants absorb nutrients from other materials. An old stand-by, it can be spread an inch or more in vegetable gardens and flower beds, used as a half-inch top-dressing twice a year on establishes lawns. Other good mulches not already mentioned include cotton gin wastes, shredded cotton burs, oat, rice and cottonseed shells, sphagnum moss, a variety of weeds, crop residues, grasses and different types of hay.

Mulching Method Using Hay

Speaking of hay leads us to the nation’s foremost advocate of year-round mulching. She relies almost exclusively on spoiled hay, which is peeled off in convenient layers, or “books,” from bales standing ready for use; or tossed on by the armful to smother a solitary weed or two that may poke through the existing cover.

How much mulch do you need? The answer to that is: more than you would think. You should start with a good 8 inches of it. How can tiny plants survive between 8-inch walls? And the answer to that is: the mulch is trampled on, rained on, and packed down by the time you are ready to plant. It doesn’t stay 8 inches high.

What about specific crops? Such acid-loving plants as strawberries, blueberries, cranberries, raspberries, peanuts, radishes, sweet potatoes, watermelons, azaleas, camellias, mums, rhododendrons, etc., do well with an acid-material mulch —most leaves, pine needles, sawdust, wood shavings, salt hay. A 1 1/2 to two-inch layer of salt hay makes the best mulch for strawberries. Pine needles are another excellent topping for this plant, and have been found effective at a two to 4-inch depth. Tests showed that mulched blueberries yielded more fruit than cultivated plantings, and that sawdust at a rate of 6 to 8 inches gave the most consistent results.

Actually, a mulch program maintained for several years will let you practically forget about acid or alkaline soil problems. Ample organic matter acts as an effective buffer and helps to neutralize extremes of pH in any soil.

Mulch Timing Is Often Important

Some vegetables, like tomatoes and corn, need a thoroughly warmed soil to encourage ideal growth. A mulch applied too early in the spring, before ground temperatures have had a chance to climb a little in frost-zone areas, may slow up such crops. Once plants are well started, though, and the weather levels off, mulch is definitely in order to conserve needed water, stimulate topsoil microorganisms, and generally condition the soil.

Early ripe tomatoes cannot be expected if the spring-thawing ground is cloaked too soon. I have learned this lesson: That if mulch is applied before the earth is thoroughly warmed, it will delay the ripening of tomatoes. I apply mulch now only when the flowers are profuse, or may even wait until the fruit sets before mulching the plants. Then the mulch seals the heat in instead of sealing it out.



For late-ripening tomatoes I mulch my plants heavily when I set them out. For the earliest possible fruit, set out enough to get ripe tomatoes in unmulched soil until the juicier and better-flavored tomatoes are ripened in the mulched rows. By the wise use of mulch you can prevent tomatoes ripening all at one time. Much the same is true of corn, despite a long-continuing difference of opinion about whether it should be mulched at all. Organic gardeners throughout the northern planting zones consistently get improved crops and growth response by mulching when plants are up about a foot high. Other vegetables which do best in well-warmed soils include the melon and cucurbit families.

Still another way mulch makes home gardening more rewarding with less work is in growing potatoes.

Large crops of the highest-quality potatoes can be grown by laying the seed (preferably small whole potatoes) on top of the remains of last year’s mulch. Make double rows, 14 inches apart, with the seed the same distance apart in the rows. The idea of this is not only to get a heavy yield, but to make it easy to inspect the vines from both sides occasionally, and take care of a rare potato bug or a bunch of eggs that the Ladybugs have missed. Having laid the seed in straight rows with the aid of a string, cover the rows with 7 or 8 inches of hay, and do nothing more until several weeks later.

After the blossoms fall, begin moving the hay carefully to see how things are progressing. Small potatoes an inch or two in diameter can be separated from their stems without disturbing the parent plants, and the hay then replaced.

As for the soil-type factor, along with curbing weeds, a carpet of mulch performs in a number of less frequently realized directions. Cultivating a hard-packed soil will favor moisture percolation and air penetration, but the dry, bare surface may be completely eroded in a flash storm. Furthermore, continued cultivation may speed up organic matter loss and thus destroy favorable soil structure.

Mulches influence moisture penetration in several ways. Bulky materials such as wood chips, sawdust and straw temporarily hold a considerable volume of water, and thus prevent loss by runoff when the rate of application — natural or artificial — is too rapid for soil penetration. This may be more important with a heavy silt than with a porous sand soil. However, maintaining the soil structure loose and open may be the most important factor involved. Rain beating on an exposed soil compacts it and subsequent baking in the sun almost completely eliminates its capacity to absorb water rapidly. The open soil structure found under a mulch is also favorable to rapid air exchange. Roots require oxygen for the respiration pro¬cess through which energy for growth is released.

Harvest and Winter Protection

At harvest time, vegetables which sprawl on the ground, such as cucumbers, squash, strawberries, unstaked tomatoes, etc., often become moldly or even develop rot. Others may be damaged by falling onto uncovered soil. A mulch prevents such injury by keeping the vegetables clean and dry, and by providing a cushioned layer on which they can rest or drop.

Besides this aid, a late-summer mulch helps to prolong the growing season. By buffering the effects of early frosts, it allows more time for second plantings or late crops to mature. At both ends of the summer, mulched soil and plants derive a noticeable benefit in this guard against weather extremes.

As Indian summer wanes and fall makes its mercury-dropping entrance, the usefulness of a mulch follows the season. There’s a somewhat different prime purpose in the fall and winter mulch, though, and it’s important to keep this in mind. Protection, especially of bulbs, perennial roots, shrubs, etc., is the objective now; protection, that is, from sudden temperature changes, from up-and-down thermometer readings which can harm overwintering plants.

The mulch now should be applied after the first hard frost to prevent alternate thaws and freezes from heaving soil, roots or bulbs. Its purpose once winter sets in is to hold the lower temperature in the soil, avoid a rise and subsequent refreezing which shifts the earth and plants, often exposing enough to cause winter killing. To protect young shrubs, and particularly roses, mound several inches of earth around them early in autumn, then mulch after the first freeze with several more inches of leaves, straw, yard trimmings, etc. Young trees can be protected from rabbit or field mouse damage by wrapping hardware mesh loosely around their base before the circle of mulch is applied. Of course, the winter carpet of organic matter also helps condition the whole garden area for the next spring.

How much mulch? The amount that does the best job for you, your soil and your plants. Working out an ideal mulch program takes some experimenting, some trials with various materials and depths. It’s only common sense to check on the most plentiful free and reasonable sources, to test the effects of different mulches in your climate locale, your own soil type and timing. But the program more than pays — in dividends of better home-grown foods, a finer soil, and happier gardeners.

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{ 6 comments… read them below or add one }

gardengirl February 20, 2012 at 5:34 am

hi there
I already have an established strawberry bed in the place I just moved into. For the winter I put about 6 inches of hay over it. Now that spring is almost here do I need to take away some? This is the first time I’ve had a garden and this is new to me. Will the established plants just grow through all that hay? thanks very much

Reply

steve February 20, 2012 at 7:35 pm

@gardengirl, As spring comes, pull back the hay, trim the dead leaves, etc and you should be good. You can leave the hay, it’s a good moisture barrier.

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Hal March 19, 2012 at 7:40 pm

I read in some gardening magazine some time ago that paper can be used as a mulch. If I fine shred junk mail, can I use it for compost? What about newspapers?

Reply

steve March 23, 2012 at 2:43 pm

@Hal, Yes you can use newspaper, junk mail, etc as mulch. I shred and compost all my paper; it’s a great source of carbon.

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Mario April 9, 2012 at 7:55 pm

So I have 2 part question…. 1) I have just planted new things in my garden (2 PeeGee Hydrangea trees, 5 wintergreen boxwoods, and 4 knockout roses) I laid down pine soil conditioner when planting since I am in clay soil, what would be the best type of mulch for these new plants? Also with the mulch suggested and plants listed what would be proper watering?

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steve April 18, 2012 at 12:58 pm

@Mario, I suggest a cedar mulch and water once a week.

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