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Organic Soil Amendment 101

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What is soil amendment, and do you need it? Soil amendment is when material is added to soil to enhance its properties, such as retaining water or improving aeration, drainage function, or structure. Don’t get this confused with fertilizer: the purpose of fertilizer is to provide plants with the elements they need so they can grow faster/more productively. Instead, a soil amendment will improve your soil’s quality when mixed in, which can be used in conjunction with fertilizer. Some amendments may also have fertilizer value.

There are all sorts of soil amendments. Here’s a listing of some of the more popular organic types and their benefits. Find out what your soil needs through testing and compensate accordingly.

What’s your favorite soil amendment? Did we miss anything? Leave a comment.

Sphagnum peat – This will help soil retain more moisture and will also provide acidity.

Wood chips – Decomposing wood chips will provide carbon to soil. Too many will suck up nitrogen, which means that you might have to add more nitrogen rich fertilizers to help with decomposition.

Grass clippings and leaves – Contain some nitrogen and trace amounts of potassium and phosphorus. Grass clippings can also increase soil water holding capacity. Fresh grass clippings are nitrogen rich, but dried out grass clippings are carbon rich. Dried leaves are carbon rich. Apply during the fall to ensure adequate decomposition time. Shredded dried leaves make an excellent mulch that will improve the soil over time.

Bone meal – Bone meal will add phosphorus and calcium to soil.

Compost – Adding compost is probably the single best thing that you can do to improve your soil. For sandy soils, it helps hold water. For clay soils, it helps loosen the soil. And for sterile soils, it adds microbial life. Making your own compost is best. If you buy compost, be careful of too much one ingredient compost, like composted cow manure or composted mushrooms. Buy bags of several different types of compost if you are doing it that way.

Manure – Use only aged or composted manure, as fresh manure has high nitrogen levels that can burn plants.

Biosolids (treated sewage sludge) – We suggest not applying to vegetable gardens. Can be okay for flowerbeds or lawn soil.

Sawdust – Very high in carbon as it decomposes. Be careful, as it may add too much carbon and suck up all available nitrogen from surrounding soil, so use sparingly.

Wood ash – Wood ash will help raise soil’s alkalinity and provide nitrogen and potassium. Use only in small amounts.

Humus – Humus will increase soil’s fertility, hold moisture, and provide aeration.

Organic limestone – This additive can help lower soil acidity.

Blood meal – A slow-release source of nitrogen for your soil.

Straw – Straw can be used to loosen soil for drainage purposes, but contains high amounts of carbon. For best results, apply in the fall or two months prior to planting.

Cottonseed meal – If your soil needs slow-release nitrogen, potash, and phosphorus, cottonseed meal is a great choice.

Paper/cardboard/newspaper – High in carbon, along with paper mill waste. Use sparingly, so as to not lower nitrogen levels too much.

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