Many of us homesteaders manage large gardens from spring to fall while the weather is perfect for growing most vegetables. However, as day length declines and the climate cools, the options for what we can grow become more and more limited. So, we tend to scale back our bed space during the fall and winter months.
Some gardeners will put their beds to rest by blanketing them with several inches of compost and mulch to prevent erosion and protect soil life all winter long. It can be an effective way to protect your garden in winter. Unfortunately, even well-mulched beds can invite invasive weeds to move into these otherwise unoccupied spaces.
An even better answer to protect soil from winter weather extremes, preserve soil life, discourage weeds and add soil fertility is to grow fall and winter cover crops.
What Are Winter Cover Crops?
Cover crops are like plant-based carpets for your garden beds. They are usually seeded at a high rate to create a dense mat of plants that act as both mulch and green manure. Additionally, cover crops can be used to help address specific problems in your soil over winter.
For example, most organic gardeners apply compost to their gardens to add fertility. Compost is good, but when applied year after year, it can sometimes lead to an excess of inorganic (not plant accessible) phosphorous in the soil.
Certain cover crops, like crimson clover, can specifically extract excess inorganic phosphorous from the soil. The plant matter from the cover crop can then be collected, composted, and reapplied as organic phosphorous that will be accessible to plants later.
Reasons to Use Cover Crops in Your Garden
A fellow master gardener once told me that we could either plant the cover crops we want or deal with the cover crops that nature plants for us. She is so right!
In nature, the soil is continuously planted. Even in winter when many plants go dormant above-ground in response to the cold, the roots below ground are still alive and benefiting the soil. Using cover crops effectively mimics how nature works in our cultivated gardens.
Cover crops can perform the following valuable functions in our gardens when we are not using our garden beds to grow food.
- Prevent erosion
- Protect soil life
- Preserve soil structure
- Prevent nitrogen leaching by rain and snow
- Add nitrogen
- Add organic matter to improve soil tilth and prevent compaction
- Provide pathogen protection
How Cover Crops Work to Protect and Improve your Soil
Now that you have an overview of the main reasons to consider using cover crops, let's take a closer look at how cover crops perform each of these functions.
1-3. Erosion Prevention, Soil Life Preservation, and Soil Structure Maintenance
Cover crop roots hold the soil in place to prevent erosion. They provide habitat for soil life such as fungi, bacteria, protozoa, and critters like worms.
The roots of cover crops also provide structure to the soil to prevent compaction from the weight of snow and beating rains. Additionally, they create spaces in the ground so air and water flow to keep soil from becoming stagnant.
All cover crops perform these services to some extent, though some may work better than others depending on your soil texture type and level of fertility.
Best All-Purpose Winter Cover Crops: Hard Winter Wheat, Annual Rye, White or Red Clover.
4. Nitrogen Preservation
For some heavy feeding crops like corn, lettuce, and cabbage, we often apply extra nitrogen fertilizer to ensure that our plants have what they need to grow quickly during the season. If plants don't use all that nitrogen, it is likely to be washed out of the soil by rain and melting snow and end up in waterways. There it can poison aquatic life.
By planting a heavy feeding cover crop like hard winter wheat, that nitrogen is held in place by the plant roots and then absorbed by the plant as it grows. This process prevents the nitrogen from leaching off and causing pollution as a result of winter weather events.
In spring, the roots and leaf mass of the cover crops can be tilled back into the soil. Biological life in the soil will break down the plant matter and return the nitrogen so the next round of plants can use it.
Best Nitrogen Preservation Cover Crops: Hard Winter Wheat, Triticale, Annual Rye, Barley, Tillage or Daikon Radish, Oats.
5. Nitrogen Fixing
Legumes like Crimson Clover, Austrian Winter Peas, and Hairy Vetch, draw nitrogen directly from the air. They then form a relationship with bacteria in the soil that help those plants store that nitrogen in nodes that form on the plant roots.
When those plants are tilled into the soil or are winter killed, the nitrogen in those nodes decomposes making that stored nitrogen available to the next round of plants in your garden. Planting nitrogen-fixing cover crops before planting heavy feeders like corn, cabbage, or lettuce, can cut down or eliminate the need to add fertilizer to garden beds.
Best Cover Crops for Nitrogen-Fixing: Crimson Clover, Red Clover, Alfalfa, Austrian Winter Peas, Hairy Vetch, Fava Beans.
6. Soil Tilth Addition and Compaction Prevention
Many gardeners till their soil deeply to break up compaction and eradicate weeds before planting their new crops. While there are benefits to deep tilling, particularly in a new garden, doing this on a regular basis destroys soil structure and ultimately leads to greater compaction, loss of soil life, and leaching of nutrients over time.
Adding large amounts of organic matter to the soil over several years effectively does what deep tilling does without the adverse side effects. The organic matter breaks up soil compaction and adds to soil structure. Additionally, organic matter becomes a feedstock for the biological life in the soil that then adds nutrients to the earth.
When you grow cover crops, they become the organic matter you add to your soil. After they are grown, and before they flower, you can either lightly till them (usually by hand) into the top few inches of soil or cut them down and allow them to decay on top of the soil.
Best Soil Tilth/Compaction Prevention Cover Crops: Oats, Barley, Hard Winter Wheat, Tillage or Daikon Radish, Mustard, Rape, Annual Rye.
7. Pathogen Protection
Some winter cover crops can perform all these benefits (except nitrogen fixing) and have the added benefit of helping minimize pathogens in your soil. These winter cover crops are often called biofumigants.
The primary biofumigants used in home cultivation are arugula and mustard. Although many varieties of these plants can have some benefits, buying cover crop seeds selected explicitly for this purpose is preferred.
When lightly tilled into the soil, the leaves and roots of these plants decompose and release chemical compounds that interrupt the life cycles of some fungal pathogens and nematodes.
Best Cover Crops for Pathogen Protection: Pacific Gold Mustard, Nemat Arugula.
How to Use Cover Crops in Your Home Garden
Now that you have an idea of what cover crops can do for your garden, you have to choose the right cover crops for your needs. There are a lot of different strategies to use.
You may need to do more research and some trials in your garden to find the strategy that works best for your needs. However, here are a few ideas to get you started.
1. The Three Sisters Approach to Cover Crops
Similar to the way people grow corn, squash, and beans together, you can also use the three sisters cover crop plan.
Traditional Three Sisters Plan
In the traditional three sisters, corn is the main crop. It is planted first. Once the corn has achieved some height, beans are planted near the base of the corn so that the corn stalk can become a trellis for the beans. (Since legumes fix their own nitrogen, they don't impact the growth rates of the corn.)
Squash is planted at intervals and allowed to vine on the ground under the corn. It acts as a living much to shade the roots and preserve moisture and minimize the need for irrigation.
Winter Cover Crop Three Sisters Plan
You can apply this logic to winter crops. Hard winter wheat, Austrian winter peas, and tillage radish make good sisters. These plants can be planted simultaneously because the wheat has faster germination and growth rates than the peas or radish. Also, the peas are field peas and don't require tall trellising.
Interplanting, as shown above, spreads the benefits throughout your soil. I plant the wheat and peas at 1 foot by 6-inch intervals. Then I plant the radish in square foot intervals. However, you can also do this in 1-foot rows for simplicity.
In early spring, the peas and wheat can be lightly tilled into the soil. The radish should be winter killed and allowed to rot in the soil to break up compaction. In warm climates, you may need to mow the tops of the radish several times to force root decomposition.
If your soil needs biofumigation, substitute mustard for radish. Plant the wheat and peas first. Start the mustard after those plants are a few inches tall to avoid shading those plants during early development.
2. The Crop Rotation Approach to Cover Crops
Another method of using cover crops is to create a crop rotation similar to what you do with your vegetable garden. Cover crops can be broken down into categories of nitrogen fixers, grasses, and cole crops to establish a rotation system.
For example, you can grow a nitrogen-fixing crop like crimson clover before you plan to grow heavy feeders like corn. Then you can grow rye, hard winter wheat, or oats (all grasses) after corn to scavenge nutrients overwinter. Finally, following your medium feeding plants, you may want to grow cole crops such as a biofumigant like mustard to prevent a build-up of pathogens or a tilth enhancer like daikon radish to revitalize soil structure.
Keep in mind as you are setting up your cover crop rotations that they should mesh with your regular crop rotations. If you are giving your beds a break from corn, then you also want to give them a break from grasses like wheat. Likewise, if you are rotating out cole crops, then don't use biofumigant cole crops during your off-season.
3. The Needs Based Approach to Cover Crops
You can also use cover crops specifically to address problems in your garden. Although I use both of the above methods, I find that a needs-based approach gives me the best results in the garden. It does require some additional study, so you should know the specific purposes of each cover crop and how to identify the needs of your soil.
As an example, if you performed a soil test and found out your soil was nitrogen deficient, then you could plant nitrogen-fixing legumes to generate more nitrogen.
Crimson clover, alfalfa, or hairy vetch would be great options for hard-hitting nitrogen fixing. However, deciding which one is best will depend on the current condition of your soil and how long of a growing season you have before winter frost slows nitrogen production.
If you had significant fungal pathogen problems in a specific bed during the growing season, then you may want to plant a biofumigant to mitigate future risks.
If your beds are organic matter light and need an infusion of green matter, then you might opt for big biomass influx by combining oats with winter peas.
Cover Crops Special Planting Requirements
Winter cover crops have basic soil requirements just like any other plant you put in your garden. They will have plant-by dates based on your most likely frost dates. They will have pH and nutrient needs that will also determine if they are suitable for use in your garden.
One of my first failures as a gardener came when I tried to plant fava beans as a nitrogen fixer in a new garden. The plants barely grew. They rotted in the first rain. Plus, they actually took nutrients out of my garden rather than adding nitrogen.
That's when I learned that nitrogen fixers only fix nitrogen when they are inoculated with the bacteria called rhizobia. Since I planted them in a new garden without the necessary bacteria, those fava bean roots didn't establish the nitrogen storing relationship to fix and save nitrogen. As a result, they used what was already in the soil (which wasn't enough to grow healthy plants).
Before you settle on specific winter cover crops, research its needs and any special instructions for successful planting. Follow applicable planting rates. Also, apply care to instructions such as seed planting depth, fertility needs, watering requirements, inoculants needed, etc. to get the best results.
Final Advice on Winter Cover Crops
Cover crops require less work than most vegetables. However, they are not care-free.
If you want a care-free cover crop, then just let nature take over. As my master gardener friend explained to me, if you allow nature to do the cover cropping for you, you are sure to grow the best possible weeds, suited to your soil quality and needs.
Since that's probably not what you want in your vegetable garden, plant winter cover crops like you mean it to reap the benefits come spring planting next year!