Cover Crops in the Garden
Cover crops can be an excellent way to build soil organic matter, recycle nutrients and control weeds. However, they must be carefully considered before planting to ensure they help, rather than hinder, the main garden crops.
Types of Covers
When deciding which cover crop to plant, gardeners should consider goals for the cover, cost, and control strategies. Start small with leftover brassica seeds such as kale and radish. This has little cost investment and will either winter kill or can be easily controlled with tillage or pulling in the spring.
Grass-like covers are best for building organic matter and soil tilth because they have such an abundant root system. Oats are inexpensive and will winter kill. Brassicas fight compaction, especially the larger radish varieties. Legumes can add nitrogen to the soil for next year’s crop. Most covers will take up excess nutrients the garden crops did not use and release them over time as they breakdown the following season.
Most covers will offer weed control simply by outcompeting weeds. Most covers are planted after the vegetable crop has finished producing for the season so the weed control is most helpful with winter annuals. If covers are allowed to grow into spring, they will continue to provide weed suppression.
Although it requires a higher level of management, cereal rye is a great option because it can be seeded late into the fall. It will also continue to grow in the spring, providing additional benefit. That also means it must be controlled. It is killed easily with a glyphosate application, tillage, can be smothered, or can also be crimped (details below). The earlier the crop is killed, the less weed control it will offer. Despite how abundant the foliage may look, if the stem has not elongated it will breakdown rapidly once killed. It is important to note that cereal rye does inhibit germination of small seeds. This adds to its benefit in weed control but can prevent small seeded vegetables such as lettuces and carrots from germinating. This effect lasts a few weeks after termination.
Crimping Cereal Rye
Crimping cereal rye to kill it must be timed exactly right to successfully kill the plant and prevent it from going to seed. It must be crimped several times up and down the stem, after stem elongation. The best time to do this is when the rye is in full flower/anthesis. Do not allow it to go much past this stage or it could reseed. Crimping can be accomplished with a sharp-edged tool such as a shovel. Farmers use roller/crimpers pulled behind a tractor for large scale crimping. To start out, try this in a small area with a light seeding rate ( 3 oz/100 sq ft) and have a back up plan such as glyphosate, smothering or pulling if the crimping does not work. However, once it is accomplished successfully, the straw cover offers weed suppression and moisture retention throughout the growing season.
|Cereal rye in full anthesis. Note the anthers (or flowers) up and down the head.|
Most covers can be planted anytime after vegetables are harvested until the end of September. The few that can be planted through mid to late October are: Winter barley, oats, wheat and cereal rye and rapeseed or kale. The later planting gets into October, the greater risk for frost damage. Two cover crops gardeners should avoid are annual ryegrass and vetch. These can be difficult to control in Ohio.
Planting can easily be accomplished by planting into rows made by a hoe or with broadcast seeding by hand or spreader across the soil. If the soil is hard, raking to create better seed to soil contact will result in greater germination.
|Cereal rye after green-up in spring.|
Starting with a cover crop that is likely to winter kill may be the least intimidating way to introduce the practice into the garden. Note that even some covers that typically winter kill may survive if planted in mid-summer and/or the winter is mild. To view how different cover crops fair through the winter, check out the Cover Crops at Farm Science Review videos at http://go.osu.edu/agcropsyoutube.
Remember that the longer cover crops are able to grow, the more benefit they provide. Also, allowing the residue of dead plants to breakdown in the garden will build organic matter. The caveat is, this can use nitrogen in the soil so additional nitrogen may be needed in the first few years of using cover crops.
Glyphosate application: This allows covers to remain on the surface to provide a weed and moisture barrier and also controls any exiting weeds. It is also the least labor intensive. Always follow label directions.
Pulling: For small areas, or as a last resort, pulling can be used to control covers. If plant material is completely removed from the garden, the organic matter benefit will be reduced. This is also the most labor intensive and time-consuming method.
Smothering: Covers can be killed like other plants by placing a barrier over top such as cardboard. This offers an herbicide free option for no-till gardens.
Tilling: This is an herbicide free way to control cover. Ensure the tiller can handle the amount of cover it will go through. This will take care of any existing weeds but will not help with weed control and moisture retention later into the season.
|Top of picture: Cereal rye sprayed and planted into. Bottom of picture: not sprayed.|
|Same bed as above. Cereal rye killed with glyphosate versus allowing to grow. Rye was sprayed 4 weeks prior to this picture, in early April.|
While there are a lot of considerations to using cover crops in the garden, there can also be many benefits. Starting small is a great way to learn what works for each garden and gardener. The Midwest Cover Crop Council selection tool is designed for row crop farmers but can offer insight to gardeners as well: https://mccc.msu.edu/covercroptool/.