How to Buy Soil Amendments

Soil amendments are substances that you add to soil to make it more beneficial for growing plants. Unlike mulch, which only sits on the surface, soil amendments are thoroughly mixed into the existing soil. Choose soil amendments with the goal of improving properties like permeability, aeration and water retention. Also consider the soil's nutritional content, with a mind to which plants you wish to grow.

1. Determine what kind of soil amendment you need. Almost all gardeners want loamy soil, which is gritty but moist, nutrient-rich and easy to till. Sandy, silty or clay soil is generally undesirable. Inspect your soil to determine its composition and test it using a soil test kit.

- Soil with less than 3 percent of organic matter should be amended with organic matter like composted manure, straw, grass clippings or wood chips.

- Amend with peat if you have sandy soil. Avoid using mountain peat, because harvesting it is severely disruptive to the environment.

- Biosolids consist of treated sewage mixed with other organic matter such as leaves or clippings. Use only Grade 1 biosolids, which are relatively free of pathogens, and only if you aren't growing root vegetables such as carrots or potatoes. Most gardeners balk at using biosolids to grow any food crops.

- Add bark or perlite to clay soils. Never try to amend clay with sand because the combination will result in a soil that resembles concrete.

2. Bear in mind that each type of amendment will change the chemical composition of the soil -- lowering nitrogen or adding phosphorous, potassium or salt. You may have to use a chemical fertilizer to make an adjustment. Select a low pH amendment if your soil tends to be high pH.

- Choose an amendment that decomposes rapidly if you want to improve the quality of your soil quickly. Use one that decomposes slowly if you want long-lasting improvement. Most gardeners mix amendments to get both quick and long-lasting improvements.

3. Calculate how much soil amendment you will need. Measure the square footage of the area and multiply this number by the desired depth. You may have to do some fairly complex calculations if your garden isn't rectangular. The more accurate your measurements, the less likely you are to buy too much or too little amendment for your needs.

4. Buy soil amendments by the bag or truckload from garden centers, nurseries, compost facilities, landscapers and tree companies, farmers markets or online. You may be able to have large amounts of amendments delivered to your garden by the seller.