A Guide to Soil Amendments

There are lots of different materials on the market that claim to be great for your soil. It can be confusing at times trying to decide what to use. Some of the most common soil amendment materials and what they’re used for are included below.  The numbers in parenthesis after the material are the approximate nitrogen – phosphorus – potassium percentages:

Alfalfa meal: (3-1-2) Pellets or ground meal from the alfalfa plant.  Good organic soil additive that contains hormones that stimulate growth. Incorporate into the soil or use as a tea.

Ammonium sulfate: (20-0-0) Fast acting, concentrated source of nitrogen with 24% sulfur; increases acidity. 

Blood meal:  (~15-1.3-0.7) Collected blood of slaughtered animals, dried and ground and containing not less than 12% nitrogen in organic forms.  Contains iron and many other trace elements. When purchasing this material, ensure that it has been steam sterilized to remove any concern regarding transmission of blood borne diseases.

Bone meal:  (~12-2-0)  Bones, hoofs, and antlers of vertebrates, which have been softened by steam and ground.  High in phosphorus and slow release.

Chelated iron: A chemically modified form of iron that makes it available to the plant; can be added to the soil or as a foliar spray for fast acting results.

Coffee grounds: (~2-0.3-0.3) The grounds from your coffee maker are acidic; use if you want to lower the pH or combine with more alkaline materials like wood ashes or limestone.

Compost: Decomposed organic matter derived from vegetative sources.  The nutrient value varies depending on materials that are composted.  Adds macro and micronutrients.

Dolomite: Carbonates of magnesium and calcium in equal proportions.  Useful for neutralizing acid soils in the same manner as limestone; supplies magnesium.

Earth worm castings: (0.5-0.5-0.3)Superb soil conditioner with no risk of burning plants; very high in organic matter.

Epsom salts:  Magnesium sulfate – 10% magnesium and 13% sulfur; magnesium is essential for good leaf growth.

Fresh grass clippings:  (0.5-0.2-0.5) Breaks down quickly; incorporate into soil or add thin layers to compost piles.

Fish emulsion:  (~4-1-1) Partly decomposed blend of finely pulverized fish.  Source of nitrogen and other trace elements.   

Greensand: 18% iron oxide and 30 other trace elements that are released slowly; loosens soil.

Gypsum:  33% calcium oxide.  Reacts with sodium or potassium carbonate to form corresponding sulfates and insoluble calcium carbonate increasing soil permeability. 

Humus:  Well-decomposed organic matter constituting from one-fifth to one-half organic matter in peat, compost, leaf mold and rotted matures.  High buffering capacity prevents soil from becoming too acid or alkaline.

Kelp meal: (~1.5-0.5-2.5)  Dried seaweed used as slow acting fertilizer with micronutrients.

Lime or Limestone:  Generic term for a wide range of agricultural materials defined as having a calcium and magnesium content.

By Nanette Londeree, Master Rosarian

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