Mulch: A Gardener’s Secret Weapon

  • Difficulty Rating: Beginner


man shoveling mulch into tractor

The gardeners at Olbrich Botanical Gardens in Madison, Wisconsin, have a secret weapon.

It’s mulch, and it comes with an excellent provenance. The rich, organic leaf mulch used on the flower beds and in the luxuriously deep shrub borders at Olbrich Botanical Gardens actually comes from trees all around the city.


leaf mulch in gloved hands


“It’s great stuff,” says Jeff Epping, Olbrich’s director of horticulture. “We use it all over the garden.”  Organic mulch — made of bark or composted leaves — helps preserve moisture in the soil, keeps down weeds, keeps the soil temperature even, and improves the quality of the soil as it breaks down. Mulch makes flower beds look tidy; a ring of mulch around trees also looks neat, and it reduces competition from grass and helps keep lawn mowers from damaging the bark.

Epping is especially committed to leaf mulch, which he prefers over wood-chip mulches; it breaks down more quickly and contributes more nutrients to the soil, he says. But all organic mulches are good for a garden.


olbrich leaf mulch


At Olbrich Gardens, leaves collected by the City of Madison are composted all winter long, shredded thoroughly by big machines, and then loaded in plastic bags for one of the garden’s biggest annual fund-raisers. Bags of composted leaf mulch — each containing enough mulch to cover a 35-square-foot bed 2-3 inches deep — are sold for $6.50 each. The garden sells about 9,000 bags of leaf mulch every year. The annual sale is in the spring, which is a great time to apply mulch. Wait until perennials are up and growing nicely, and then spread mulch throughout your flowerbeds, tucking it in around the crowns of plants (but not too close to stems). Refresh mulch rings around trees in spring, too, and spread mulch around and under shrubs.


mulch with flowers


If you have a tree, you have everything you need to make leaf mulch in your own back yard. Rake autumn leaves and pile them in a corner of the garden, or make an enclosure (three feet by three feet is a good size) to contain the leaves. Mowing over leaves and collecting them in the lawn mower’s bagger before piling them up is even better: moisture penetrates through leaves when they’re not matted down, and smaller-sized particles will not blow away in the wind. Crushed autumn leaves also start to break down more quickly than whole leaves, and this decomposition creates an environment that supports an abundance of beneficial microbes.

In a vegetable garden, mulch cool-season crops (such as broccoli, brussels sprouts, and cabbage) immediately after setting transplants out in the garden. Let the ground warm up before you mulch around tomato transplants, or around the seedlings of squash, cucumbers, and other warm-season crops.


straw with lawnmower


Ben Sharda, director of Kansas City Community Gardens in Kansas City, Missouri, mulches his vegetable garden with shredded straw. He buys bales of straw at a local feed store, spreads the straw on his driveway, and mows over it with the bagger attachment on his lawnmower. The shredded straw is easy to spread in a two-inch layer around the plants, and it breaks down over the course of a single season.


spreading straw mulch over raised bed


“Mulch doesn’t last forever, but that’s the way it needs to be,” Epping says. As it breaks down, organic mulch improves the quality of the soil, which makes plants stronger and healthier. To keep this virtuous cycle going, just add more mulch.