In September we discussed how important soil quality plays in successful gardening and how vital organic matter was. Green Manure cover crops are a major way to provide organic matter to your garden and protect that valuable soil.
We give the name Green Manure to any crop grown only to be turned into the soil to improve it’s quality. Green Manure benefits the soil in many ways:
- It reduces wind and water erosion.
- Cover crops hold nutrients otherwise lost over the winter.
- Green Manure provides organic matter.
- Its roots help break up the soil and keep it loose.
- Cover crops are a good indicator of soil problems.
- Legume cover crops can increase the nitrogen level in the soil.
Cover crops have been used for years to reduce water and soil erosion particularly during the winter months. When the soil freezes, the surface becomes very dry, similar to freeze dried oranges, and is very susceptible to erosion. The plant’s root system locks the soil in place and prevents compaction of the surface.
Green Manure crops take up excess nitrates in the soil that would normally leach out during the cold weather months. When tilled in, the plants release the locked up nitrogen back into the soil.
Cover crops are a good indicator of potential soil problems to the observing eye. By watching how the cover crop grows, we can spot areas that need attention. You can be assured that if the cover crop does not grow well in an area, there is an underlying problem that will adversely effect your garden.
Green Manure crops should be planted, when possible, in late summer or early fall to become established before winter. This will vary from location to location based on your weather pattern. Here, in Southwestern Lower Michigan, in hardiness Zone 5, the crop should be sown before Mid-September. The following are some common cover crops, recommended planting times, and seeding information.
| Cover Crop | Planting | Seeds/100sf |
|---|---|---|
| Annual Rye | September | 5-10 oz. |
| Winter Rye | September | 5-10 oz. |
| Oats | September | 5-10 oz. |
| Winter Wheat | August – October | 5-10 oz. |
| Buckwheat | Summer | 5-10 oz. |
| Clover | Summer | 1-4 oz.. |
| Barley | September | 10-15 oz. |
| Fava Beans | October | 12-14 oz. |
To be useful, your selection should germinate rapidly, produce abundant and succulent tops, and grow well in the site conditions. It is often better to use a legume because of the benefits of the nitrogen fixation and the microbial activity it promotes.
In the spring, you will want to turn the cover in at least two weeks before you plan to work the area. This can be done by rota-tilling, plowing, or using a spading fork if the area is small. It is often helpful to mow the crop before tilling. The nitrogen held in the Green Manure’s tissue will now be available to future crops through decomposition.
Cover crops can be a valuable tool to the home gardener in developing high quality soil when used correctly. Green Manures are an inexpensive way to produce organic matter and protect your soil. Take time this fall to try it.
