Mulch: the great cover-up

Flower & Garden Magazine, June-July, 1995 by Marianne Binetti

WHEN A LEAF FALLS IN THE woods, it is not likely that anyone would pick it up. Leaves, plant litter and other organic debris cover the forest floor, grass layers build up over the prairie and rocks and gravel top off the sandy soil in desert areas. No matter what the climate or topography, the soil in nature is covered with some kind of mulch. It pays for us to apply this lesson in our home gardens as well, to reap the benefits that nature has enjoyed from the beginning.

FOUR REASONS TO MULCH

Smother out weeds. A mulch on top of your soil reduces weeds in two ways. First, it blocks the weed seeds that blow into the area from above by providing a less hospitable germination bed than bare soil. Second, it blocks many weed seeds already in your soil that may try to sprout up from below. The deeper the mulch, the more weeds you will block.

For more effective weed blocking, lay down a three-page layer of newspaper before applying your mulching material. The newspaper will provide an additional weed barrier and will decay into the soil over time.

Conserve moisture. Water evaporates more quickly from soil that is left naked. A mulch not only shades the soil from the hot sun, but organic mulches soften the earth and improve aeration as they slowly decompose. This softening encourages plant roots to reach down deeper, where they are more likely to find moisture on their own.

Maintain constant soil temperature. Do you ever find your plants uprooted or dislodged after a hard winter? Changes in soil temperatures from alternate freezing and thawing cause plants to be heaved from the ground. A heavy winter mulch will stabilize these winter fluctuations and keep your plants' roots planted firmly in the ground.

Cover up a multitude of sins. Let's face it: a newly mulched bed improves the look of the entire garden. Mulches cover up dips, rises, rocks and plant debris. Spreading a fresh mulch can work a lot like a fresh coat of paint.

COMMON TYPES OF MULCH

Gravel. Gravel is a durable mulch that will not blow away or decompose. However, since it doesn't decompose, it does little to improve soil quality. Gravel is difficult to shovel, spread and transport, and you must rake or blow it regularly to keep it looking tidy, as garden debris stands out against a gravel mulch.

Bark. Tree bark comes. in many sizes, from finely ground or shredded for flower gardens and seed beds to chunky pieces, each an inch or two long. Bark is an attractive mulch that improves the soil as it decays. It can rob the soil of nitrogen, however, so some gardeners fertilize their barkmulched beds with a few handfuls of cottonseed meal or another slow-release form of nitrogen. Finely ground bark can blow around in strong winds, which means you may need to reapply it frequently.

Hay. Hay decomposes rapidly and is a good source of nitrogen for soil. It is also inexpensive if you can find a source of spoiled hay, but looks messy and can add huge amounts of weed seeds to your soil. To avoid this problem, use second- or third-growth hay that has not gone to seed.

Straw. Usually sold in rectangular bales, straw is the stiff stems of wheat, oats or other grain crops. Some grain seeds are often mixed in, but straw tends to be less weedy than hay. Its coarse appearance makes it better suited for vegetable gardens than shrub or perennial borders. Straw resists matting down, even when wet.

YARD AND GARDEN REFUSE AS MULCH

Grass clippings. Grass decomposes rapidly, adding nitrogen to the soil. Its appearance improves once the fresh clippings dry and it can be mixed with peat moss for maximum benefit. Be sure to apply grass in layers less than one inch thick to keep clippings from matting. If layered too thickly, fresh grass clippings may give off an unpleasant odor or heat up the soil enough to damage plants. Wait one week after applying a weed killer to lawns before gathering the clippings for mulch.

Leaves. Fallen leaves add many nutrients to the soil. A 4- to 6-inch layer forms an effective weed barrier, is a good soil insulator in winter and conserves water in summer. Unfortunately, leaves look messy and can blow about unless they are finely chopped. For better appearance, run your leaves through a mower or chipper/shredder or use older leaves that have turned into leaf mold. Chopped leaves may mat together and prevent water from getting to your plants.

Wood chips. Wood chips offer a nice appearance along with good weed control, soil insulation and water conservation. However, they decompose slowly, borrowing nitrogen from the soil in the meantime. Wood chips should not be used near structures since they can attract termites and carpenter ants.

Compost. With its rich, dark appearance, compost is attractive as well as an excellent source of nutrients. It also retains moisture well and is a good insulator. Making your own compost requires time, though, and it decomposes quickly. Furthermore, sources of good, inexpensive packaged compost are scarce.

Pine needles. The flexible needles of white pines make a fine-textured mulch; other pines have more rigid, longer-lasting needles. Fallen needles can be raked up from below pine trees. As a mulch, they stay loose and dry, and have a slight acidifying effect on the soil below.