Cover Crops & Soil Enhancement
What to Do Off-Season in the Edible Garden
Putting the garden to rest
Thanks to Marin's mild winter weather, home gardeners can grow vegetables year-round. But you may choose to give the garden (and yourself) some rest and rejuvenation once you've harvested your last summer-fall crop. Here are two options for putting the edible garden to bed before you kick back in your easy chair and flip through seed catalogs.
Two basic options for your edible beds:
> Grow cover crops
> Straw-covered manure layer
Option one: GROW COVER CROPS
Cover crops are plants grown primarily to improve soil. Planted when traditional garden crops are not present, they enrich soil and provide numerous other benefits. Cover crops are often referred to as a “green manure.”
Advantages
• Build soil fertility
• Increase soil organic matter
• Suppress weeds
• Protect soil from wind and water erosion
• Provide habitat for beneficial insects and earthworms
• Loosen soil without digging, as roots reach down deeper than any shovel
• Fix nitrogen in the soil. Research shows that legume crops, especially vetch, are the best for nitrogen fixing.
• Suppress some harmful soil-dwelling nematodes: Mustard plants do this naturally.
• Provide aesthetic addition to winter gardens.
Disadvantages
• May require watering, at least until fall rains keep soil evenly moist.
• Cutting down the crop and digging it into the garden bed is work.
• Patience is required while the chopped material breaks down in the planting bed. Alternatively, put greens in the compost pile.
TIMING: when to plant and cut down a cover crop
Planting cover crop seed at the right time is important for success.
September or October: Sow cover crop. To enhance the soil for spring edibles, avoid planting cover crops after November.
February or early March: When cover crops are 25-50% in flower, cut them down, chop them up, and dig the greens into the soil 3 to 6 weeks prior to planting. The buried material will decompose and provide nutrients and organic material to the soil while increasing biological activity, water infiltration, and soil tilth. Shredded cover crop may also be added to your compost pile instead of digging it into the bed.
Example: Plant cover crop on October 1, cut down on March 1, plant tomatoes and other spring crops on April1-15.
Any time of year: Plant a cover crop at any time to enhance a tired bed, as long as the crop planting is consistent with the growing season.
HOW TO PLANT a cover crop:
• Inoculant: Some UCCE (University of California Cooperative Extension) Farm Advisors recommend inoculating legume seeds prior to planting to effectively fix nitrogen. Legumes work with bacteria called Rhizobium that live on their roots, and allow the plant to fix nitrogen into the soil. Buy inoculant where you buy cover crop seeds.
• Planting depth is based on seed size. In general, the larger the seed, the more soil cover it requires. Follow instructions on seed package and the suggestions below.
• Rake the soil smooth, removing any significant debris from a previous crop.
• Broadcast the seed at the recommended rate for the plant type.
• Cover the seed with soil to the recommended depth for the plant type.
• Water if necessary and keep moist until rains begin.
WHAT TO PLANT
Choose a cover crop based on your goals:
Improve soil structure
Plant deeply rooted plants and/or plants with large biomass such as barley, rye, and daikon radish.
Build soil microbial biomass
(fungi, bacteria and other microbes): Plant Phacelia.
Protect the soil from erosion
Plant grasses, mustard, and radish.
Suppress weeds
Plant grasses, mustard, and radish.
Attract beneficial insects
Plant mustard and radish.
(These plants may also attract undesirable insects such as cucumber beetles and stink bugs).
Increase nitrogen
Plant vetch and other legumes.
Seeding for the season
Common Cover Crops for California are included in the chart below. Once you’ve identified the desirable crop, check with local nurseries or online seed suppliers for availability.
Option two: LAYER OF MANURE COVERED WITH STRAW
A rice straw-covered layer of manure is another way of boosting soil.
Advantages
• Works slowly over the winter to enrich soil
• Attracts earthworms
• Feeds legion of beneficial microbes needed for healthy spring crops
• One-and-done deal; there is nothing to cut down in spring like there is with a cover crop.
Disadvantages
• Sourcing, transporting, and shoveling manure
• A smelly wait for a couple of days for the barnyard aroma to dissipate
HOW TO LAYER IT UP
• Pile on 2 or more inches of herbivore-generated manure (horse, chicken, cow, goat, llama and rabbit are all equally good (preferably from animals that have not been treated with antibiotics or other pharmaceuticals).
• Top it with a fluffy layer of rice straw (often available inexpensively at horse or farm supply stores) or dry leaves three times as deep as the manure layer. The straw stays neat-looking for months, and thick layers of organic material smother most weeds.
• Winter rains keep the pile moist, attracting earthworms and helpful decomposers.
• Straw and leaves hold in moisture and prevent rain from compacting the soil.
• In spring, turn the composted manure and straw into the top layer of soil before planting.
BACK TO EDIBLES
> What Edible Gardens Need
> Best Choices for Marin
> How to Prepare
> How to Plant
> Edibles in Containers
> Planting Calendar
> Grow & Care Sheets for Vegetables, Herbs & Fruits
> Tips & Techniques
> How to Maintain
> Fruit Trees
> Top 20 Edible Garden Problems
> Cover Crops & Soil Enhancements in the Off-season
> Conserving Water
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