Green Thumbs Value a Good Mulch

It is often said that there are no new ideas in gardening. And certainly all the best ones are older than the human race.

Take mulch, for example. For millions of years -- long before anyone scratched a line in the soil with a rock and dropped seeds into it -- plants have been casting their leaves on the ground as a protective covering for their roots and a nursery for their seedlings.

As leaves decompose, they add nutrients to the soil and give it the nice loose structure that plants love. Earthworms pull the leaves into the soil, digest them and excrete them as rich castings. Soil microbes feast on them, turning them into compounds that plants use.

The leaf blanket prevents soil from eroding and rain from running off or evaporating. It moderates the soil temperature, keeping it cooler in summer and warmer in winter. It discourages the weedy annuals that colonize bare soil and compete with the plant's' progeny.

A good organic mulch does all these things for your garden too. If you apply leaves, stems, roots or other parts of decomposing plants, you will have to water much less, and crops that need consistent moisture, such as tomatoes, will have a steadier supply.

A damp, cooler soil will help keep your potatoes free of Colorado beetles. It's true! I've seen an unmulched and a mulched planting side by side -- the first infested, the second, not.

Hardy crops such as kale, leeks, spinach, carrots, parsnips and celery root will usually survive the winter with a good mulch layer.

Ripening fruits that lie on the ground stay cleaner and more disease-free on a layer of mulch. This includes melons, squash, unstaked tomatoes or cukes, and strawberries.

Best of all, a mulch applied to a weed-free ground will keep most new weeds from growing, and those that do come up can be easily pulled in that nice friable soil. This feature is as kind to the gardener as it is to the crops. It is essential for permanent plantings such as raspberries and asparagus where invading grass and weeds might ruin the crop. Fruit trees such as apple have been shown to be more productive with a straw mulch layer. And most annual vegetables benefit from mulching as well.

I prefer mulches that break down readily in the soil and are easy to lay down. I used to buy salt hay, which grows in coastal marshes, because the seeds it contains don't germinate in gardens. But it's less available now, so I use straw or hay. These come off the bale in flakes, like the volumes in an encyclopedia. I lay them in rows on either side of a crop or a seed furrow. If weeds come up in a flake, I just flip it over.

Other good materials include leaf mold, pine needles, shredded bark, grass clippings and wood chips, but you can use just about any plant matter -- chopped cornstalks, pea vines, even dead weeds, as long as they haven't gone to seed.

Not everybody mulches, and few do it with as much fervor as the mother of all mulchers, Ruth Stout, author of "How to Have a Green Thumb Without an Aching Back." She simply applied eight inches of hay to her garden and replenished it without ever tilling the soil. Her books created a mulching revolution.

Maybe it's a coincidence, but most of the mulchers I know are women. Would it be a sexist generalization to say that men like attacking weeds with hoes and watering crops with hoses, and women like tucking things under covers?

Perhaps mulchers are just people too busy to weed.

My husband, Eliot, says he doesn't mulch because his closely spaced rows leave no room for mulch. I think it's because the soil in his garden looks so dark and rich from home-made compost that he can't bear to hide it.

Then again, it does pay to be a cautious mulcher. In a cool spring, I wait for the soil to warm up before putting mulch down. And I always water dry ground, before mulching it. I keep mulch away from plant stems, to avoid rot.

If slugs or voles are a frequent problem in your garden, mulch may not be for you. Once my sister Anne, in a very wet year, put down black plastic sheeting with wood chips on top. "It was like a bad horror movie," she says. "The garden became a swamp. I came home from work one evening to find a slug population of Biblical proportions. They were just draped all over the potato vines, like a weird Dali painting."

Black plastic used alone will warm up the soil for heat-loving crops like peppers and melons, and I've done just that in cold climates. But it's ugly. The only thing worse is the red plastic designed to mulch tomatoes. Supposedly it makes them think they are being crowded by other plants, and this stimulates faster growth.

For myself, I'll stick to what falls from the trees or grows in the ground. It's been working for gardeners ever since Adam delved. And Eve mulched.