Green manures are plants that are grown to benefit the soil, usually in organic gardens. There are many to choose from, and many factors to consider when choosing the right plant to grow in your situation.
- Decide how long the green manure will be in place. Green manures are usually planted on soil that would otherwise be bare for several weeks, or which is being newly cultivated. How long the green manure has to grow is a key factor in choosing which green manure to grow. For example, buckwheat and phacelia have short life cycles and would normally be grown for only a few weeks before being dug in. Hungarian grazing rye and winter fares can be left in place over winter, and alfalfa is used for long term coverage -- it can grow for over a year.
- Think about your soil. Like all plants, different green manures have different soil requirements. Buckwheat thrives on poor soils, but clover requires a good loam. Alfalfa doesn't like acid soils, and neither do winter tares. Hungarian grazing rye grows very well on heavy soils.
- Have a wish list. What soil improvement are you hoping for? Green manures can suppress weeds, control soil erosion and nutrient loss, improve the soil structure and even add nitrogen into the soil -- but they don't all do all of those things. Decide which improvements you're looking for.
- Don't forget to factor in the season. In spring and early summer you will have a large number of green manure plants to choose from. As the year goes on, your choice decreases. In the fall there are only a couple of green manures that will thrive.
- Consider the next use of the soil. What the soil will be used for after the green manure is also important. If the soil is in your vegetable garden then you need to consider your crop rotation; many green manures are members of vegetable plant families and need to follow your rotation. Some, including Hungarian grazing rye, inhibit seed germination. This makes them good weed control plants, but means that you shouldn't use the soil they've been growing in as a seedbed -- at least for the next few weeks.
- Short list. When you've taken all these factors into account, you may have a short list of potential candidates or you may only have one choice. If you have a short list then the final choice is just a matter of convenience for you.
Choosing a green manure does not need to be daunting, but for the best results you need to do your homework and find the one that is best for your garden. Once you've done that, it's just a case of sowing the seeds and leaving the plants to grow!