What is a Soil Amendment?
Whether a beginner or expert, many gardeners find that their garden does not always come with the perfect soil. Soil can be too wet or dry, too acidic or alkaline, or not have enough organic material to properly satisfy the needs of particular plants. In these cases, extra material needs to be added in order to have healthy soil and plants.
Soil amendments are materials that are added to the soil to improve its biological, chemical, or physical properties. They can come in many different forms – it depends on what the soil is lacking specifically. To know where to start, it’s important to identify the issue with the soil first.
How to Do a Soil Test
A soil test measures pH levels and identifies any elements that may be missing from the soil. Fortunately, soil tests are relatively easy for anyone to procure. All you must do is contact a local agricultural extension office, and they will send a test kit you can use to collect soil and send back to them. When they receive your samples, they will run tests to make sure the soil has balanced pH and contains healthy amounts of nitrogen, phosphorous, potassium, and calcium.
If there are not any local extension offices available, soil tests can also be done DIY. If you put soil in a bowl and mix it with vinegar and the mixture fizzes, that means the soil is alkaline. If you mix it with baking soda and it fizzes, that means its acidic. Another viable DIY method is the earthworm test: healthy soil should have about 10 earthworms per cubic foot, so if you dig up a nice pile of soil, you should be able to check easily. 
Once you have identified any specific problems with the soil, then you can begin finding the best soil amendment for your garden.
Soil Amendments to Increase Nitrogen and Phosphorous Levels
Compost is a rich source of organic matter and nitrogen. Adding it to the soil can increase nitrogen levels and improve fertility.
Manure helps improve soil structure and is also a great source of nitrogen.
Fish Meal is an excellent source of nitrogen and phosphorous that increases microbial activity in the soil and improves root development in plants.
Rock Phosphate is an excellent nutrient source and helpful for preventing calcium deficiencies.
Soil Amendments to Raise pH
If your soil is too acidic, there are many kinds of soil amendments at your disposal to bring it back to a more a neutral pH. A more alkaline soil is generally advantageous for growing vegetables and greens.
Agricultural Lime is made from ground limestone and contains calcium and magnesium carbonates, which help bring more alkalinity to the soil.
Dolomitic Lime is similar to agricultural lime, but contains more magnesium. It is great for soils that are low in magnesium and have a low pH.
Calcitic Lime is a type of agricultural lime that only contains calcium carbonate. If the soil already has adequate magnesium levels, this may be the better choice.
Soil Amendments to Lower the pH
Plants such as blueberries, raspberries, azaleas, rhododendrons, hydrangeas, and evergreen trees and shrubs all thrive in lower pH soils.
The best soil amendments to use to reduce pH are elemental sulfur, aluminum sulfate, and ferrous sulfate. Sulfur reacts with bacteria in the soil to form sulfuric acid and release hydrogen ions, which lowers the pH of the soil.
How to Amend Soil
- Water the soil around the plants. This helps the soil amendments mix with the soil and reduce the risk of root damage.
- Sprinkle the soil amendments both on top of the soil around the plants, making sure not to get any on the leaves, flowers, or stems of the plants. Use a hoe to work the amendments into the soil surface.
- Water the soil again after applying the amendments. This will help amendments settle into the soil and begin to work.
- Add a new layer of organic mulch. This helps to retain moisture in the soil, suppress weeds, and gradually add organic material to the soil as it breaks down.
- Monitor the plants in the weeks and months afterwards to see if they are healthy or need more help to grow.
The types of soil amendments you need for your garden depend on what plants or crops you would like to grow and the nature and health of the soil. Make sure to identify particular issues with the soil first, and then choose what would be the right amendment. If any questions come up, Monster Gardens is a great resource for information on soil amendments as well as a repository for many of the best organic brands in gardening.
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