Cover crops (or "green manure") keep the soil active through the winter months.Plant in vacant beds in late summer-early fall (early enough for the seeds to germinate) and till/cut into the soil with garden hoes and rakes as soon as you can work the ground in early spring. Cover crops have several benefits - they enrich the soil with organic matter, and help improve soil structure, reduce erosion and weed control.
Follow these steps for planting cover crops:
1. Rake the garden area smooth and remove all debris.
2. "Broadcast" or scatter the seed across the surface of the garden bed.
3. Finally, rake lightly again and water with your hose set at a fine mist.
The following cover crops are easy to grow and recommended in youth gardens. They can be purchased in garden centers or farm stores.
Garden Hint. Explore the benefits of cover crops with your students by conducting a before-and-after experiment: test your soil before planting any of these crops, and then again the following season. What changes do you see? How has the use of green manure amended your soil?
Winter Wheat
Although typically grown for the purpose of harvesting and selling, winter wheat provides many benefits as a cover crop. It is a good form of erosion control and enhances cycling of nitrogen, potassium, and phosphorus. It competes well with most weeds and is less likely than barley or rye to become a weed itself. Wheat prefers well-drained soils of medium texture and moderate fertility. If soil is poor, rye may be a better option.
Winter Rye
Rye is the hardiest of cereals, and can be seeded later in fall than other cover crops. It outperforms all other cover crops in infertile, sandy, or acidic soil, but will also grow in heavy clays and poorly drained soils. Rye also attracts significant numbers of beneficials such as ladybugs.
Rye can establish in very cool weather. It will germinate at temperatures as low as 34° F. Rye grows and matures rapidly in the spring, absorbing nitrogen in the process. Plowing under the rye before it reaches 18 inches could reduce the nitrogen uptake and keep the soil from drying out, but gardeners in more humid climates may prefer to wait until after the spring rains.
Crimson Clover
Crimson clover grows rapidly and provides early spring nitrogen for full-season crops. Quick fall growth, or summer growth in cool areas, makes it a good choice for shorter crop rotations as a weed suppressing green manure. Its flowers are eye-catching, which makes it visible even in a mix with other flowering legumes.
Crimson clover will grow well in about any type of well drained soil, especially sandy loam. It often does poorly on heavy clay, waterlogged, extremely acid or alkaline soils. Once established, it thrives in cool, moist conditions. If the pH is low, it is recommend to use lime to ammend your soil. However, it takes about 6 months for soil to be altered - so ammendments should be added in early spring (soon after receiving those soil test results), to be effective by fall.
Seed six to eight weeks before the average date of first frost. A pre-September seeding date is recommended, but in warmer climates the seeding period can be extended until mid-November.