Cover Crops

Why Cover Crops?

Cover crops don’t usually provide an edible harvest; but they are worth growing for the benefits they provide to your soil and the garden ecosystem.

Different varieties can provide one or a combination of benefits such as: provide biodiversity to attract and provide food for beneficial insects and soil organisms, mine minerals from deep in the soil, discourage weeds, prevent erosion and leaching, retain moisture, combat diseases and harmful soil organisms, break reproduction cycles of harmful insects, regulate soil temperature, provide living mulch, and supply your soil with organic material. Cover crops are so beneficial to your garden that they are often referred to as green manure.

All cover crops supply essential organic materials to the garden when they are cut to decompose in place. They are usually planted after edible crops are harvested. Cover crops can also be grown instead of or among edible crops. With so many reasons to grow cover crops and so many different ones to choose from, how do you know which ones to select? Your choice depends on the season and what you want to accomplish. There are three basic types of cover crop plants. Mixtures of multiple types are also good and provide a wider range of advantages for each planting.

Types of Cover Crops

Grains/annual grasses like rye, oats, and wheat. These cold-hardy crops are usually planted in fall in our area. They have deep roots which break up compacted soil. They reduce nematode populations and accumulate potassium from the soil which is recycled when cover crops are cut to decompose in the garden.

Legumes like field peas, clover, and vetch. Field peas are planted in summer while clover and vetch are cool season crops. These nitrogen-fixers capture nitrogen from the atmosphere to supply their needs and those of immediately following crops.

Broadleaved crops like buckwheat, mustard, and rapeseed. Buckwheat can be planted in most seasons, but will not survive freezing. Mustard and rapeseed are cool season crops. These plants germinate quickly to shade out weeds, and they easily decompose for a quick release of nutrients.

Site Preparation and Planting:

Lightly cultivate with a rake or a broadfork to prepare a place to plant. Broadcast seed evenly over prepared area and cover with a very light layer of fine mulch, compost, chopped leaves, or garden soil. Alternatively, pat firmly and cover with light row cover until germination to protect seed from birds. Water thoroughly but gently so as not to displace seeds. About one-fourth cup of seed is adequate for an 8' x 4' bed (32 sq ft) to provide weed suppression. Up to one cup can be used for heavier and faster coverage, and to add more organic matter to your soil.

Termination: Cover crops should be cut while in full bloom, but before they set seed. Here’s why:

• Allowing cover crops to grow until flowering maximizes their contribution to soil organic matter and nitrogen (legumes).

• Cover crops that are cut before they flower may regrow and become weeds among your veggies. Allowed to set seed, crops may reseed and appear in subsequent seasons where you don’t want them.

Chop and Drop or Incorporate your cover crop?

The ultimate object of terminating your cover crop is to return the nutrients contained in the cover crop tissue to the soil for use by microorganisms and subsequent crops. This is called nutrient cycling. When the time comes to terminate your cover crop, you have two options:

Chop and Drop:

Cut the plants down to ground level using clippers, hedge shears, a small sickle or a weed eater, and leave them as mulch on the soil surface. DO NOT pull up the plants – leaving the roots to decompose in place reduces disturbance of microorganisms, aerates the soil, and preserves organic matter. You can speed up decomposition by adding a mulch of leaves or pine straw on top of the chopped cover crop and watering.

Chop and drop before transplanted and large-seeded crops (tomatoes, peppers, squash, etc.).

Advantages: Best for soil quality (reduces microorganism disturbance); provides the same advantages as any other mulch—discourages weeds, conserves moisture, etc.; less labor.

Incorporation:

Use a shovel or hoe to chop the plants and work them into the top 3-5 inches of the soil. Grass cover crops can be more persistent and may need this method.

Advantages: Creates better planting space for small‐seeded crops, like carrots or lettuce. Wait several weeks to a month before planting to allow decomposition to get under way. Also best for terminating legumes when planting crops like greens that benefit from nitrogen. Subsequent crops can be planted right away as nitrogen is volatile and will begin to dissipate as soon cover crops are terminated.

Disadvantages: Disturbs microorganisms, less weed control than cut-and-mulch; may activate dormant weed seeds, lots of work!

Regardless of termination method, subsequent crops can be planted by moving aside remaining cover crop residue and planting in the soil (no-till). Plant remnants act as a mulch and continue to provide nutrients through decomposition.