Garden basics: the differences between mulch and compost

A look at two soil conditioners.

Dean Fosdick/AP
Brown Gold: This homemade compost was made fromkitchen scraps, yard litter, and garden waste. It's a nutrient-rich soil amendment.

Compost and mulch. Both are great soil conditioners, but how do they differ?

Each serves as a time-release fertilizer and insulator.

When augmented with livestock and poultry manure, nutrient-rich compost leaches into the earth and feeds countless microorganisms, earthworms and fungi.

With time, watering and mixing, discarded green kitchen scraps, yard litter and garden wastes decay into crumb-textured "brown gold" — a greatly enhanced growing medium.

Mulch, meanwhile, is a protective cover that also works its way into the topsoil. It's made up of natural or synthetic substances — everything from crushed rock and plastic sheeting to wood chips, discarded newspapers, and straw.

Mulch minimizes gardening chores by smothering weeds, conserving moisture, eliminating erosion, and aerating packed soils. It also protects tender plants from frost and cold in winter, and from evaporation and heat stress in summer.

Compost generally is applied as a soil amendment in late fall or early spring in layers one to two inches deep. Coarse mulch then can be layered over the enriching compost to protect young plants from the elements.

Both are available for little or no cost, but there are some cautions about their use.

Regarding compost:
— Beware nitrogen burn. I planted a shoulder-high blue spruce on a hillside several years ago and covered its root ball with a new batch of manure-rich compost. It was too new and too rich. The tree soon took on the look of a discarded Christmas tree by dropping its needles and turning copper in color. It was dead, the victim of a too-hot compost and an overeager gardener. The moral of the story? Allow compost to mature before using it.

— Don't introduce weeds into your garden by way of the compost bin. Inspect plant and garden debris before adding it to the pile.

— Place composting sites well away from the house. Decomposition often produces unwelcome odors. Decaying mixtures frequently attract insects and snakes. The operation also might be unsightly. Consider screening it.

— Leaves decay more quickly when shredded. Grass breaks down faster when turned. Adding such things as seaweed, livestock and poultry manures loads the blend with nutrients. Wood stove ashes contain potassium and sweeten acidic soil. Coffee grounds perk up acid-loving plants like blueberries, azaleas and rhododendrons and help loosen compacted ground.

— Don't spread compost over edible garden crops if any of its components were sprayed with a pesticide.

Regarding mulch:
— More is not necessarily better. Mulch can over-winter bark-gnawing voles and other plant-killing critters.

— Don't pile mulch directly against tree trunks or shrubs. It can smother them. Rake it instead into a doughnut-like pocket where water can collect.

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