What are garden soil amendments?
Garden soil amendments are materials which are worked into the soil to enhance the soil’s physical properties. Good soil is the foundation of every successful garden. Unfortunately few gardens come with soil that is ideal for growing plants; nutrient rich, well draining while still holding water long enough for plant roots to access it, a nice, crumbly tilth. Since gardeners cannot count on nature to supply all the essentials, they will have to be added by the gardener.
There are several reasons garden soil amendments might be recommended for your garden or lawn. The 2 most common are to improve the soil’s texture and to correct the soil’s pH.
Improving Soil Texture
Often soil is low in organic matter, necessary for the structure, water retention and life of your soil. Organic matter includes: compost, composted manure, peat moss, coir, leaf mold and any other plant or animal remains or waste products. This may not sound like something that would be good for your garden, but organic matter can quickly change the texture of your soil as well as encourage beneficial organisms to set up home in your garden soil. Here’s a quick test to determine the texture of your soil.
Adjusting Soil pH
You might also add amendments to alter the soil’s pH. The pH of the soil needs to be within a range that will allow plants to access the nutrients in the soil.
Some plants prefer a slightly acidic or alkaline soil and many require a soil in the neutral range of about 6.5 to 6.8. You will need to test your soil to determine what its current pH is. You can buy a kit for this at most garden centers or you can have it tested at your local cooperative extension office for a nominal fee.
Once you know what your soil pH is and what range your plants prefer, you will get instructions on how much lime to add, if your soil is too acidic, or how much sulfur to add, if your soil is too alkaline. Ideally you should test your soil every year.
Garden soil is always in flux. Plants deplete it of nutrients, rain washes nutrients away, and even heavily amended soil will eventually revert to its natural state. You will need to amend your soil on a regular basis. How often will depend on the soil you are starting with. Once you get to know your garden soil, you will have a better sense of what amendments your garden will need.
The best practice you can get into is using organic matter in your garden, whenever possible and the easiest way to do that is to start and use a compost pile. Put those pulled weeds, vegetable peelings and garden debris to good use. You probably won’t be able to make enough compost for all your needs, but it’s a good start and it’s free.
Composted materials won’t necessarily add much in the way of nutrients, but they will encourage a balanced ecosystem that will keep the nutrients and soil pH in check, while they improve the texture and drainage of the soil.
Types of Soil
- Clay soil contains a high percentage of clay and silt. The particles are small and cling together, holding water and nutrients well. However, clay soil is susceptible to compaction, which can make it difficult for the moisture and nutrients to reach plant roots and for roots to penetrate the soil. You can identify clay soil by its sticky, slippery feel and its tendency to cling to garden tools.
- Sandy soil is composed of larger, coarser particles. It drains quickly, but it isn’t effective at holding moisture and nutrients. This type of soil feels rough and doesn’t hold together well.
- Loam has a good balance of clay, silt, sand and organic material. It’s the best type of soil for gardening, providing drainage and retention of moisture and nutrients. Loam holds its shape when you squeeze it lightly and is easier to dig than other types.
The soil in your landscape will likely not be ideal initially, but soil amendments can help you improve it, allowing your plants to thrive.
Common organic soil amendments are listed below:
- Sphagnum peat moss absorbs water, slowly releasing it for use by plant roots. It lightens clay soil, providing aeration, and adds mass to sandy soil, helping prevent the leaching of nutrients. Don’t confuse sphagnum peat moss with decorative sphagnum moss, which is primarily a floral design product.
- Humus consists of decayed organic matter. It improves fertility and aeration and helps soil hold moisture.
- Composted manure is an odorless farm byproduct. In addition to improving aeration and moisture retention, it enriches the soil. Dehydrated manure is a similar product that contains less moisture.
- Mushroom compost is a mixture of straw, peat moss and other organic components, formulated for use in commercial mushroom production. The mixture is used for one round of growing and then packaged as an amendment for the home garden.
- Topsoil is commercially produced compost that’s usually partially decomposed. Because of its rough texture, use topsoil in the yard or mixed with other products, and not as a potting soil.
You can also find inorganic soil amendments:
- Lime raises soil pH, reducing acidity.
- Sulfur lowers soil pH, increasing acidity.
- Gypsum improves aeration of compacted soil, helping it drain more efficiently.
- Perlite improves aeration and drainage.
- Vermiculite improves moisture retention and aeration.
- Builder’s sand is coarse sand that can improve soil drainage.
Many gardeners choose to make their own soil amendment by composting. Read Making Compost for tips on creating this nutrient-rich amendment.