Mulch is complicated.

It can be made of almost anything. Most people think first of chopped-up bark or wood waste that people put on their gardens. It usually comes in plastic bags or is sold by the cubic yard at garden centers. That is middle-ground mulch.

Companies also sell plastic mulch, either long strips of the same plastic used to make trash bags or chips of plastic blobs that look a bit like bark mulch. That type is at the unsustainable edge of the spectrum.

Then there is natural mulch: leaves, pine needles, chopped-up brush and tree limbs, straw, hay and similar items. It probably goes without saying that these are inherently sustainable.

People use mulch as a way to avoid bare soil. Bare soil attracts weeds, both irksome and invasive. Weeds sprout quickly in disturbed soil because buried seeds are brought to the surface and once the light hits them, they come to life, explained Shawn Jalbert, a native-plant grower and consultant who owns Native Haunts nursery in Alfred. Mulch keeps those seeds in the dark.

Mulch also improves the soil.

The benefits of mulch include “maintaining steady soil moisture, averting erosion, preventing evaporation of ammonia, nourishing a beneficial community of microbes and earthworms, and more,” Industry resident Will Bonsall writes in his “Essential Guide to Radical, Self-Reliant Gardening.”

So there’s no question that mulch is useful. But walk or drive around your neighborhood, and you’ll probably notice an awful lot of gardens and commercial landscapes, say the land around a bank or those strips in mall parking lots, that are mostly mulch dotted with just a very few trees or plants. Not good. While mulch helps the soil, it does nothing for wildlife, offering no food – no pollen or nectar – and no shelter. A lot of wildlife has a tough time already as we increasingly encroach on its habitat; do we really want to make it even harder?

In a talk I attended last year, Thomas Rainer, co-author of “Gardening in a Post-Wild World,” said something about American gardeners’ overuse of mulch I liked so much I’m going to repeat it: “Gardeners believe they have to act like a middle-school dance chaperone. Once things start rubbing together, they think they have to step in and pull them apart.”

So how can gardeners use mulch appropriately?

First, a note on what not to do:

“People think they can put down landscape fabric and put mulch on it, and it will prevent weeds. It won’t,” Dan Jaffe, a propagator and stock bed grower at New England Wild Flower Society in Framingham, Massachusetts, said at a talk last month at the Maine Audubon Society in Falmouth. I almost stood up and cheered.

Most of the weeds in a garden come from seeds that land through the air, and they will sprout, Jaffe said. Let me expand: The roots of the weeds that do sprout will go through the landscape fabric and create a huge mess. When you then try to weed, the chore will be five times as hard.

Back to what you should do – Jaffe said that he and the rest of the staff at the Wild Flower Society’s Garden in the Woods use mulch as a tool in new gardens, with the emphasis on “new.”

“If a garden is more than five years old and still has mulch showing, you need more plants,” Jaffe said.

Plants do everything that mulch does for a garden, he said, and they do it better.

To fill a garden quickly, Jaffee suggested plugs, which are tiny perennials that come in about 1-inch-square plastic pots. Plugs adapt more quickly to the garden than larger plants do, and they cost less. Divide the recommended planting distance between each plug by three, so you end up planting three times as many plants. When gardeners use that method, they probably won’t have to add plants after five years.

Traditional garden wisdom says that plants so close together will compete with each other for nutrients. That is true to an extent, Jaffe said, but they also support each other, sharing mycorrhizae, which help provide nutrients.

Another technique is to use low-maintenance plants in place of mulch. Jaffe likes Canada mayflower, a low-growing, clumping species that spreads quickly. My wife Nancy and I have some of this. We never planted it, but it showed up and is spreading nicely in a shady area near our driveway.

Ground phlox also work well, Jaffee said. He particularly likes the divaricata and stolonifera varieties, which grow thickly in shade; phlox subulata needs sun and won’t grow as thickly. Tiarella cordifolia, or running foam flower, also creates a thick ground cover, with long-lasting white flower spikes.

Jalbert recommended hay-scented fern. “It’s a wonderful groundcover that really thickens and has a tendency to out-compete any weed,” he said.

Virginia creeper also covers a lot of ground, he added. It is aggressive, though.

Jaffe said the plants he mentioned are ideal, but even if you nave a non-native like white clover, that’s far better for the ecosystem in your garden than bare mulch or lawn. As for the violets that cover much of our yard? He approved.

To return to types of mulch. Leaves make the best mulch, according to Jalbert in an interview, Jaffe in his talk and Bonsall in his book. Jaffe said Garden in the Woods used to grind up the leaves, but no longer bothers as the whole leaves work fine. Jalbert differentiates between types of leaves: If he wants to add nutrients, he uses maple or basswood. If he wants a more sterile product, he goes with oak leaves or pine needles.

Bark mulch and wood chips are good if you can get them at a decent cost.

But, please avoid plastic.

ABOUT THE WRITER

TOM ATWELL is a freelance writer gardening in Cape Elizabeth. He can be contacted at: tomatwell@me.com