Sweet Treats for Soil
27 Mar 2012
Creating a sustainable soil environment is crucial to growing vigorous plants. Here’s a guide to organic fertilizers that will help your soil become healthy.
Text and Photos by David Wann
A Well-Balanced Diet
Generally, conventional fertilizers contain the “big three” nutrients—nitrogen, phosphorus and potassium—but rarely contain dozens of other trace elements that support growth and help prevent disease. Colorado soils are particularly deficient in water-retaining organic matter and available nitrogen. They’re also high on the pH scale, an alkaline condition that many crops don’t like. Soil pH above 7.3 inhibits plant uptake of essential nutrients like phosphorus. Garden staples like lettuce, corn and peppers prefer a pH just below neutral (7 on the pH scale), while tomatoes, strawberries and potatoes prefer an even more acidic soil. The good news is that soils high in organic matter can buffer pH extremes, effectively allowing for good yields, even if soil pH is on the high side. Adding a 2- to 4-inch compost layer to beds every year is a good practice (see mastercomposter.com/pile for complete information on composting). Adding peat moss, leaves, coffee grounds and pine needles can also lower pH levels slightly, but the most effective health food for high pH is elemental sulfur in quantities up to 10 pounds per 100 square feet, which is expensive unless bulk supplies are available.Compost Can’t Do It All
Compost organisms perform a very valuable service by making naturally occurring nutrients available in the soil. But eventually those nutrients become depleted. To offset what is harvested from the garden, return composted garden residue to the soil, along with other composted goodies like food scraps, leaves and manure. If you have space or time constraints, high-quality compost can be purchased at reasonable prices. Eko Compost, for example, performs well, because it has a low ratio of carbon (i.e., not too much sawdust) to nitrogen, which is supplied with materials like alfalfa meal and poultry manure.- Once you know what your soil lacks you can add natural organic fertilizers to enrich it. “Whole-food” fertilizers are expensive, but the quality of crops is much better than those grown with cheaper chemical substitutes, says author David Wann, preparing a bed for his strawberries.
- Most Colorado soils are high on the pH scale, an alkaline condition that some crops don’t like—particularly strawberries, tomatoes and potatoes. High soil pH is best mitigated with elemental sulfur, but peat moss, leaves, coffee grounds and pine needles will slightly lower pH as well.
Alfalfa meal | Supplies organic matter; high in nitrogen and potassium |
Blood meal | High in nitrogen |
Bluegrass hay | Good balance of nitrogen, phosphorus and potassium (NPK) |
Bone meal | High in phosphorus; also good for nitrogen |
Chicken manure | High in nitrogen and phosphorus |
Coffee grounds/black tea leaves | High in nitrogen; lowers pH |
Compost (homemade) | Moderate levels of NPK |
Cottonseed meal | High in NPK |
Cow manure | Good food for the beneficial soil organisms |
Eggshells | High in calcium; good for nitrogen |
Elemental sulfur | Lowers pH |
Epsom salts | High in magnesium and sulfur |
Fescue hay | Good balance of NPK |
Fish meal | High in nitrogen and phosphorus |
Granite meal | High in potassium |
Greensand | High in potassium and trace minerals |
Hairy vetch | Good winter cover crop that supplies nitrogen |
Kelp meal | High in potassium; contains 60 trace elements |
Oak leaves | High in potassium |
Peat moss | Good for organic matter; slightly lowers pH |
Pig manure | High in nitrogen |
Rock phosphate | High in phosphorus |
Sheep manure | High in nitrogen and potassium |
Soybean meal | High in nitrogen |
Worm castings | Contains 11 trace elements |