PHOTO: Oregon State University
March 22, 2016

By now, you’ve probably heard that mulch is an essential component of a successful farm or garden. Garden mulch is a layer of organic material that is spread on the ground to protect or improve soil. Mulch materials can range from “brown” mulch (carbon)— shredded leaves, newspaper, straw, or wood chips—to “green” mulch (nitrogen)—grass clippings, cut weeds or herbs or manure. It can also contain compost soil and living mulches. While it’s common practice to put mulch down in the garden at the end of the growing season, mulches also help in the spring garden and throughout the growing season.

Here’s what you need to know in order to integrate mulching into your gardening schedule.

Why Mulch?

Mulching is a simple act that can cause big benefits to your growing season. As you’re waiting for your spring seeds to germinate so you can transplant them into the garden, refresh the beds with a layer of mulch to create a welcoming habitat for your new crops.

  • Mulch Insulates and Protects: It insulates soil to protect soil organisms and plant roots from extreme weather, as well as insulate them from sudden fluctuations, such as freezing temperatures, drying sun or compaction from heavy rains.
  • Mulch Improves Diversity and Soil Health: It protects soil organisms, like worms, insects, and soil microbes, which will help protect against pests. These soil critters work double-duty: As the soil organisms break down the mulch, it will enrich the soil. Mulch also helps to prevent soil erosion, allowing you to keep more of your healthy soil right where you want it: in your garden.
  • Mulch Regulates Moisture: Because mulch will reduce evaporation, it helps maintain even moisture level, protecting soil organisms and plant roots from shock and cutting down on the need to water.
  • Mulch Reduces Weeds: This works in two ways: first, reducing the amount of sunlight weed seeds are exposed to so fewer germinate, and second, by preventing weed seeds from settling on soil and germinating. Researchers at Michigan State University discovered that the brown leaf mulch’s suppression of weeds increased when paired with a green mulch source, such as grass clippings.

Mulch According To Climate

In cold, dry climates, deep mulch will help to insulate the soil from fluctuating and extreme temperatures and help to reduce evaporation, while in cool, wet climates, a deep mulch could be detrimental by preventing air circulation and the evaporation of excess moisture. Keep this in mind as you work your garden. If the latter describes your garden conditions, use a light mulch that will allow the soil to breathe while still preventing soil compaction and erosion in heavy rain.

Seasonal Mulching Considerations

mulch and compost
Pippa Buchanan/Flickr

Spring Mulching

If temperatures are already heating up and drying out for you, then a healthy layer of mulch will be beneficial to your spring garden. On the other hand, if spring is typically a cool, wet season, then go light on the mulch this time of year.

Here in my Ohio zone-6a garden, I keep my garden deeply mulched in the early spring to protect against late cold snaps until I’m ready to plant. At the time of planting, I pull back the mulch to direct seed, then cover the seeding with a light layer of shredded leaves or straw. This allows the seeds access to air and sunlight for germination but reduces disruption from birds and squirrels.

Cover crops are typically sown in the fall and turned under in the spring before planting. Ideally, cover crops will be cut at the soil level in the spring, about a month before planting, and then incorporated into the soil either through tilling or by using a digging fork. Breaking up the roots at this time will make planting easier, too.

As the season goes on, adjust the amount of mulch used to reflect the climate—deep mulch for hot, dry climates and light mulch for cool, wet climates. Annual living mulches, such as sweet alyssum or nasturtium, can be seeded in between planting rows. Not only will the flowering plants cover the soil surface, but they will also attract pollinators and repel pests.

Fall Mulching

Fall is an excellent time to feed the soil in the vegetable garden. Apply soil amendments or fertilizers, then top them with green mulch or animal manure, and finish with a brown mulch. This will protect and nourish the soil over the winter. Fall is also a good time to plant a cover crop.

Get Mulching!

Mulch should never touch the stems of plants as it can cause disease. Green layers are typically laid first, and then topped with brown layers. Apply a layer of mulch that is 1 to 4 inches thick—less in wet/warm areas and more in dry/cold areas.

When choosing your mulch materials, watch out for herbicides. Certain mulches, like grass clippings and straw, can be laden with herbicides that will contaminate the soil and reduce plant vigor. If you intend to use either of these materials in your garden, it will be wise to know their source.

Leaves should always be shredded before using as mulch and green plant matter should be chopped into smaller pieces, because both can form a thick mat that will reduce the soil’s ability to breathe. Aeration is good for healthy soil.

If using paper, use black and white (not glossy) shredded newspaper. It won’t look the prettiest, so consider topping it with compost soil if aesthetics are a concern.

Depending on the size of your garden, mulching may take a couple hours to a couple days of heaving lifting. But by taking the time to give some extra care and thought to your soil at the beginning and end of each gardening season, you’ll cultivate soil that will support the growth of healthy fruits and vegetables that you’ll enjoy for years to come.


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