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Supporting Healthy Soil Through the Cool Season with Mulches and Cover Crops

It’s tempting to clean up the entire garden, clear all debris and leave a clean slate. But leaving soil bare also makes it susceptible to compaction, nutrient loss and opportunistic weeds in our maritime winter. As rainwater flows unobstructed through bare ground, it carries small soil particles, minerals and microbes into groundwater systems where they are lost to the garden. Here are a few simple ways to prevent loss of valuable topsoil and nutrients that can feed the garden for seasons to come.

Cover Crops Serve Multiple Functions

Growing cover crops over winter is trendy in organic gardening for good reasons.

  • Cover crops deflect rain water with their leaves and absorb it through roots.
  • Legume cover crops cooperate with beneficial microorganisms to store nitrogen in the soil, making this essential nutrient available for the next season’s plants.
  • Flowering cover crops like crimson clover, which blossoms early in spring, provide food and habitat for beneficial insects.
  • All cover crops increase diversity, making the garden more resilient to disease.

Cover crop seeds can be sown under existing crops or broadcast throughout a garden bed in July-October. Fava beans are the most likely to sprout after a late (October or November) planting. Their vertical growing pattern allows them to fit in smaller spaces, like between overwintering crops. Check out the Maritime Northwest Garden Guide pages 117-118 for a full list of cover crop options.

Mulches Feed the Soil

Mulch is a layer of organic material such as wood chips, straw, leaves, grass clippings, garden debris, or compost placed on the surface of the soil. Mulch has several helpful impacts:

  • Absorbs water, slows the flow
  • Prevents weeds from sprouting
  • Regulates soil temperature by buffering it from the elements
  • Increases nutrient levels in the soil as it breaks down over time
  • Provides habitat for a variety of beneficial organisms
  • Prevents compaction by minimizing impact of seasonal rains
  • Protects the soil, prevents nutrient leaching

Different mulch materials decompose at different rates. Nitrogen rich materials such as veggie garden debris or grass clippings will decompose much faster than carbon rich materials such as wood chips or tree leaves. In order to be effective all winter long, fall mulches require a higher ratio of carbon rich materials. Fall leaves are the perfect addition and easy to access.

Burlap, Remay, Plastic Row Covers

If you’re using burlap to tidily cover the garden, be sure to place organic material such as leaves or garden debris between the soil and burlap since the burlap alone cannot feed the soil ecosystem nor soften the blow of heavy rain. Make sure there is no plastic twine in the burlap that might break down in the soil, creating microplastics. Cardboard can be used the same way, with any tape removed.

Remay, or a floating row cover, can be purchased at hardware or gardening stores and is used the same way as burlap. It’s important to stake or weigh down floating row cover so that it won’t blow away.

Plastic row covers can help protect garden beds from the rain, but they should be suspended on a cloche, or hoop house, instead of lying directly on the soil, to prevent anaerobic conditions.