The Right Way to Mulch Your Garden

Author:Terry Baldwin
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Photo by Jens Johnsson on Unsplash

Most gardeners understand that mulch helps plants flourish. But simply dumping bags of bark chips over your petunias might cause more harm than good. This post will tell you how to mulch your landscape beds the right way—depending on the season and type of garden—so your plants will stay happy and growing.

In spring

Because mulch helps maintain soil temperature, let the ground warm up before mulching new transplants and seedlings in the spring—mulch too early and the soil will stay cold longer and that could kill the roots, according to David J. Williams, Department of Natural Resources and Environmental Sciences, University of Illinois Cooperative Extension.

Annual vegetables and flowers

The best mulch for annual vegetable gardens and flower beds is an organic material that breaks down quickly—compost, chopped leaves, herbicide-free grass clippings or straw. In the fall, dig this mulch into the soil to improve it for next year, J.E. Klett, Colorado State University Extension landscape horticulturist and professor, says.

Don't use wood mulches with annuals for a couple reasons. First, wood chips reduce sunlight (which seeds need to germinate) and can be allelopathic, meaning they give off chemicals that can stop seeds from sprouting. 

Second, wood mulches can reduce nitrogen levels at the soil surface, which can inhibit growth of veggies and annual flowers, which are shallow rooted. This is not a problem for deeper-rooted perennial plants, trees, and shrubs, says Dr. Linda Chalker-Scott, an urban horticulturist and associate professor at Washington State University.

Perennial plants

In early spring, remove any mulch covering the tops of these plants after you see new growth. Perennial beds look nicer mulched with wood chips, bark, pine straw, and cocoa bean hulls (use cocoa mulch with caution if you have dogs). According to the University of Massachusetts Center for Agriculture, Food and the Environment, herbaceous perennials only need "2 to 3 inches of mulch." Too much mulch against the stems could make them rot.

If you can't see much of the ground under your perennials, you don't really need a decorative mulch. Save your money and use compost or chopped leaves. 

Mulch piled against woody perennials, shrubs and trees can be a cozy hideaway for rodents. The little stinkers will enjoy snacking on the bark, killing your plant! Keep mulch 6 inches from the base of woody plants, advises J.E. Klett. Learn the right way to mulch trees here

In fall

Autumn is an ideal time to transplant perennials, trees and shrubs. To encourage root growth before winter, J.E. Klett advises mulching fall transplants right away to maintain soil temperature as the weather cools. The roots will continue growing as long as the soil is warm.

In winter

snow covered twigs
Photo from Unsplash

Winter can be tough on fall transplants and less cold-tolerant perennials. To protect them from cold, drying winds and frost heave (when plants are literally shoved out of the ground during thaw-freeze cycles), cover completely with 4-6 inches of mulch after the ground freezes, says the Chicago Botanic Garden.

Tip: recycle your Christmas tree—small evergreen branches work well as winter mulch.

More mulch tips

  • Keep organic mulch loose to allow water and air to move in and out of soil, says J.E. Klett.
  • Don't pile mulch over tough perennial weeds - they'll just laugh and force their way up through it, so remove them first, the University of Massachusetts advises.
  • During dry spells, mulch can cake. Break it up so water won't roll off it, the Michigan State University Extension says.