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Garden Soil Amendments and How to Use Them

Here’s some information on the many possible amendments you can add to the soil in your organic garden, and how best to make use of them.

Manure

Fresh manure should not be placed on areas where crops are currently growing because it can actually burn the crops. The sole exception to this rule is rabbit manure. Manure needs to be composted first, or spread on fields that haven’t been planted yet. When you buy bags of manure, it is usually composted manure. The manure hasn’t completely degraded, but it should have lost enough nitrogen to the atmosphere that it will help rather than harm your plants.

Certified organic farmers don’t use manure in quite the same way as conventional farmers. They don’t use sewage sludge, and they don’t use fresh manure on crops less than 120 days from human consumption in crops where the edible portion touches the ground, and 90 days where it does not. While most gardeners aren’t worrying about becoming organically certified, it is worth being careful with manure because fresh manure can contain E. coli. If you have a source of fresh manure that you want to use in your garden, simply compost it before use and you’ll be fine.

Green Manures

Green manures are when you grow a crop and then turn it under to increase soil fertility. Legumes are popular green manures as they add nitrogen to the soil. Legumes used for green manures include Vetch, Crimson Clover, Fava Bean, and Field Pea. Non-leguminous green manures include Cereal Rye, Winter Wheat, Buckwheat, Typhon and Corn Salad. You can grow a mix of legume and non-legumes sown together as a green manure. Some of the non-legumes, such as cereal rye and winter wheat, add larger amounts of organic matter to the soil than legumes do, even though they don’t fix Nitrogen.

The plants should be turned under when they start flowering, as they get woodier and take longer to compost after this. Of course, this means you don’t get a harvest, but you aren’t growing them for human eating, you are growing them for improving the soil.

Compost

Compost adds nutrients to the soil as well as improving soil texture and water retention. If you have a garden, you should compost your garden and kitchen waste. This prevents your garden losing fertility every time you mow the lawn or get rid of weeds. Using kitchen waste actually adds nutrients and allows you to improve your soil over time.

Composting is a subject unto itself. At its simplest, you pile a bunch of organic matter into a heap and leave it to rot for a year or two. This looks ugly, and takes up a lot of space and time, so people in cities typically use various types of composters. Some are pretty, some are bear-resistant, some are home-made.

Lime

Unlike the other soil amendments described here, lime is not aimed at improving soil texture, organic matter content, or nutrient content. Lime increases pH, which reduces soil acidity and improves the availability of nutrients already present in the soil. Note: before adding lime, check your soil pH. If it’s already neutral (7) or higher you should not add lime as too-high a pH can also be bad for plants. The ideal pH for most plants is between pH 6 and 7.