Mulch Ado About Mulch

Mulch is a valuable gardening tool. It helps control weeds, maintains soil moisture, stabilizes soil temperature, and the organic types promote microbial activity in the soil. Plastic and gravel are inorganic mulches. Organic mulches include various chipped or shredded wood products, hay, straw, grass clippings, pine needles, shredded leaves, paper, and compost.

Plastic is easy to use but it doesn't break down in the soil and it has to be anchored in place. It does have one distinct advantage over other mulches--it warms the soil. Using black plastic can increase the soil temperature by as much as 10 or 20 degrees.  This speeds germination of seeds and the initial growth of warm-season crops such as tomatoes and peppers. Once plastic mulch has warmed the soil sufficiently, it can be covered with organic mulch such as straw.  This keeps the soil from getting too warm and looks better.

Regular black plastic won’t allow water or air to reach the soil. The black or red garden plastic mulch sold in most garden stores has very small perforations in it. Some people recommend the red kind for growing tomatoes, as the light reflected back to the plants is supposed to encourage growth and fruiting.  Don’t use clear plastic as mulch because weeds can grow under it.

Gravel and small stones are attractive mulching materials, but leaves, twigs and other debris can get down into the gravel and can be hard to get rid of, even with a blower. If the gravel used for a path is too deep, it can be like walking on marbles. You also have to use edging to keep gravel in place.

Hay or straw will contain weed seeds.  Straw will contain less than hay.  You can leave it out for a year so that heat and cold have a chance to destroy most weed seeds, or you can open the bales and let birds pick through it.  Perhaps the best course of action is to put the hay or straw on a compost pile, making sure the pile heats up to at least 160 degrees, a temperature that destroys nearly all weed seeds.

Grass clippings make good mulch, but take care not to apply them more than an inch thick. Grass clippings can form a dense mat that water and air can't penetrate, so you should keep them fluffed up. Make sure they don’t come from a lawn that has been treated with herbicides.

Most mulch that you can buy is made from wood and bark.  Be careful not to pile it too thickly though. Mulch piled on top of emerging perennials in early spring can cause the plants to rot. If placed too close to woody plants, it provides a refuge for mice and voles which can girdle the bark, killing the plant. If it is piled around the base of trees, it can encourage rot, even in mature trees. Applying too much mulch, more than two to three inches, can prevent water from penetrating through the mulch. Too much mulch can prevent the soil from warming up properly in early spring, slowing plant growth. That's why it's best to wait to apply fresh mulch until late in the spring, and then again in the late fall to serve as an insulator.

Freshly chipped wood used as mulch will steal nutrients, mainly nitrogen, from the soil as it decomposes. Either compost the chips for several months first or apply a high nitrogen fertilizer such as blood meal over the mulch. A source of chipped aspen mulch is Bessemer Plywood where a pickup truck full can be had for thirty dollars.  Do not use cocoa bark mulch if you have pets which might eat it. Cocoa bark contains theobromine, which is toxic to dogs.

I have started using the scrap wool left over from sheep shearing as mulch around the base of fruit trees.  It allows water to penetrate even when compacted, and the nitrogen in the wool is released very slowly.  I use a plastic trunk protector to make sure the wool doesn’t come in contact with the trunk of the tree and to discourage mice, voles, and rabbits from chewing on the tree bark. Elsewhere, I use the bedding material that I clean out of the sheep or llama barns which consists of spilled hay and manure.