Anything that improves the condition of the soil can be called a soil amendment. Mulches and top-dressings also improve the soil, but it’s easiest to use the word amendment or even soil conditioner to refer to anything that is turned into the soil. If something is left on the surface without being mixed into the soil, it’s either a top dressing or a mulch.
I love soil amendments! While you can grow a garden in our soils without amending it, you will find that your plants will flourish, be more productive and be less prone to pest and disease issues then without amending it. A better producing garden is much more fulfilling and less frustrating, agreed?
Soil amendments improve clay soil aggregation, increase porosity and permeability. They improve aeration, root depth and drainage.
In sandy soils, soil amendments increase the ability to hold water and nutrient holding capacity.
When should soil amendments be used? This will depend on what you are using and how broke down the matter is you are using. If most of the material has already decomposed, as with mature compost or well-aged manure, you can add it just days before planting. If you’re using unfinished compost or material that hasn’t yet broken down, such as newly fallen leaves, clean (chemical free) sawdust, or fresh manure, allow at least four weeks before planting. I prefer to add fresh material in the fall so it has all winter to break down into usable form.
There are so many choices of soil amendments. The softer finer materials are best for soil amending (compost, manure, peat moss). Hard materials take to long to break down (wood chips, sticks).
Here is a list of just a few materials that can be used as soil amendments:
Compost: Of course, top on my list would be compost! Whether you make it or buy bagged compost, it is an excellent source of organic matter. Finished compost can be used anytime. Unfinished compost should be turned under in fall or several weeks before you wish to plant. Finished compost should be dark and smell like clean earth. Work in 2-4” of compost to garden beds.
Leaf Mold: Leaf mold is an excellent source of organic matter; can be used anytime. The microorganisms in the soil love this stuff! It will help retain moisture and add healthy tilth. Generally you will have to make it yourself. But this is easily to do. Here is a link how.
Peat Moss: Peat Moss supplies organic matter and will slightly acidify soil (lower pH), so this is excellent for our soils. Be sure to mix peat moss into the soil, as it could repel water if left on the soil surface. Peat moss can hold a lot of moisture making it helpful in drought conditions. Work in 1” of peat moss to garden beds.
Coconut Coir: Coconut coir is a very nice substitution for peat moss. It comes in a compacted block that needs to hydrated before it can be used. However, it does not lower pH like peat moss does. Be sure your coconut coir you are purchasing is rinsed! If it isn’t you will be introducing salts to your garden, which we don’t need. Work in 1” of coconut coir to your garden.
Manures: Manure is an excellent source of organic matter and it supplies many nutrients, but can contribute to salt build-up, so they’re not good to use if your soil is already salty. Worms love this stuff! Work in 2” of well rotted manure into your garden soil. Fresh manure can harm plants due to the elevated ammonia levels. Avoid this by working into the soil during the fall time and letting it rest through the winter months.
Worm Castings or Worm Compost: Perfectly pH balanced! Worm castings contain minerals and highly active bacteria and enzymes. They protect soil and plants from diseases and help retain moisture. A little goes a long way. Work in up to 1/4” of worm castings or worm compost into your garden soil.
Wood Products: While wood chips and chemical free saw dust are growing in popularity, they can tie up nitrogen in the soil and cause nitrogen deficiency in plants. Microorganisms in the soil use nitrogen to break down the wood. Over several months to years, as microorganisms complete the decomposition process, the nitrogen is released and again becomes available to plants. It’s always best to compost wood products, before using them as soil amendments.
Greensand: Greensand supplies no organic matter, but help loosen clay soils and improves water and nutrient retention in sandy soils. It is rich in slow-release potassium and micronutrients. Personally, I wouldn’t grow without it. Add in the fall or early spring. Work in 2-5 pounds per 100 square foot of garden area.
Gypsum: Gypsum supplies no organic matter. It corrects soil structure problems caused by too much magnesium or sodium. May help loosen clay soils. Supplies plenty of calcium without changing the pH, so don’t use where calcium levels are already high. Not good for acidic soils.
Perlite and Vermiculite: Both of these soil amendments have no nutrient value. Perlite is best for clay soils to help the porosity. Vermiculite will help sandy soils retain moisture.
Shrimp Meal and Crab Meal: Both of these meals not only amend the soil, but they offer many benefits to the plants and soil. Microorganisms in the soil feast on shrimp meal and crab meal, making a more lively soil, in turn stimulating plant growth and health, while adding a slow-release fertilizer as well. These amendments are powerhouses for controlling devastating soil nematodes.
A word on Biosolids and/or composts containing biosolids. Biosolids are byproducts of sewage treatment. They generally contain heavy metals, pathogens, and salts. Biosolids are approved for use in production of agriculture, however, it is advisable to avoid application to vegetable gardens due to the potential for heavy metals. They can be found alone or composted with other organic matter. Compost containing biosolids can be found very cheap by the truck load. But, is cheap worth it?
There are so many choices of soil amendments. You can mix and match to what your soils needs are. So know your soil! But one thing is for sure. You can never go wrong with my favorite, COMPOST!