June 26, 2011

Maine Gardener: Mulch can mean life or death for your plants

By Tom Atwell tatwell@mainetoday.com
Staff Writer

Mulch can make your garden healthier and easier to maintain. It also can kill your plants.

It all depends on how you use it.

"Mulch" is one of those words that has so many meanings, you have to depend on context to know what is meant. You put mulch on perennial and shrub borders to keep moisture in the soil and slow the germination of weeds. You mulch tender plants in winter to help them survive. You can even put lots of mulch on lawns and fields to kill what is growing there so you can plant something else.

I like mulch. All of our gardens have 2 or 3 inches of mulch in and around the shrubs and perennials. We don't add mulch everywhere every year, but we do check where it is needed and add some.

There are gardeners who prefer to leave their garden soil bare. They consider it more natural. I wonder if they have ever taken a walk in the woods. The forest floor is filled with decomposing twigs and leaves because no one rakes there. Mulch in gardens is simply organic matter to replace the leaves we rake away.

We use a mulch that is mostly shredded bark, although it also has some chopped-up twigs and branches. It is a fairly dark brown. We don't like the looks of red cedar mulch.

The bark mulch is usually aged for a while, letting decomposition begin. If you put down freshly chopped wood chips, they would break down and add organic matter to the soil eventually, but it would take longer. And the decomposition would rob some nitrogen from the soil.

Avoid mulches created with construction or demolition debris -- and some are. They have the same problem as freshly chipped wood, and you don't know what other chemicals you are getting.

Coastal Maine Botanical Gardens uses NutriMulch from New England Organics. That is mulch mixed with decomposed sewer sludge, and the nutrients feed the plants.

I have seen people use pea stone or other small pebbles as mulch. In some specialized formal settings, that can work. But the stones often get dirty, and are difficult to clean. I have read about mulch made from ground-up tires but, thankfully, have never seen it.

It's best to mulch gardens in very early spring, before most perennials are out of the ground. The perennials will simply grow through it. But spring is busy, and too often we end up mulching around plants. If the plants are already up, you don't want lots of mulch touching the plant stalks. Have almost none right next to the plants, and more in the open areas.

This is especially true for trees and shrubs. In parking lots, you often see what landscape professionals call "volcano mulch." You have a tree struggling to grow in a 2-yard square of soil surrounded by a sea of asphalt. Mulch has been stacked a foot high around the trunk of the tree, which eventually kills the tree by smothering the roots. Every tree has a root flare, and the mulch shouldn't go above that flare.

In a summer when there are soggy periods followed by long dry periods -- and that is every summer in Maine -- a crust will form, making it more difficult for rain to penetrate.

When that happens, I work through the garden with a hula hoe, also called a stirrup hoe or scuffle hoe, and fluff the mulch. It is something you will probably have to do only once a year, and it also gets rid of any weeds that have managed to grow through the mulch.

For protecting plants from winter cold, the mulch material of choice is old-fashioned straw, but if you have pine needles on your property, they work well. You'll want to wait until late November, when the ground has just frozen, to put down that mulch.

I mentioned early in the column that mulch can kill plants, and putting volcano mulch on trees and smothering perennials will do that.

But sometimes you DO want to kill plants. Say you want to create a vegetable or flower garden where you now have lawn or a hay field. In the fall, put down layers of newspapers over the area you want to kill. Lots of newspapers. Just another good reason for keeping up your subscription.

On top of the newspapers you put on mulch, mixed with compost, about 3 inches deep. The lawn will not have decomposed completely over that first winter, but you can dig through the mulch and plant. And eventually, all the sod will decompose and enrich the soil for your future garden.

Tom Atwell can be contacted at 791-6362 or at

tatwell@pressherald.com

 

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