Many organic producers swear by rock powders. When you read about the extraordinary results produced by them, you realize that they are among the best of organic fertilizers. Any kind of organic matter is going to improve your soil’s capacity to retain water. They will also keep nitrogen in the soil and make nutrients available to plants.
All about rock fertilizers
- Rock fertilizers provide trace elements to the soil as they break down slowly. You should apply them with organic matter since they do not supply any nitrogen. They last from 5 to 10 years.
- Phosphate rock is a source of phosphorus and trace elements including zinc, boron, iodine, iron oxide, iron sulphide, calcium fluoride, calcium carbonate and manganese dioxide. It’s not soluble in water, but stays put in the soil so it’s always available for use when the roots finally reach it. Superphosphate is treated with sulphuric acid. This makes it more soluble but also more expensive because it uses so much energy in production. It’s easy, of course, and that makes it very tempting. It can cause imbalances in soil microbes and a build-up of salts. I used it with great abandon until I found this out.
- Granite dust is an excellent source of potash. It has trace elements and is a lot cheaper than chemical potash fertilizers. It won’t change the pH and is slow to release. You can use it as a top dressing.
- Potash rock contains potassium plus a wide variety of trace minerals. Apply with organic material straight into the soil or the compost heap
I use composted sheep manure, which has a higher nitrogen content than cow manure – sheep digest more efficiently than cows. Some organic gardeners don’t like the idea of using any kind of animal by-products, though this hasn’t bothered me so far. We now know, however, that the gases produced by cows burping methane are adding to the greenhouse effect.
There is a never-ending supply of animal manure: one cow will produce 27,000 pounds (12,250 kilograms) a year of which only about a third is returned to the soil without being damaged. Manure contains a high content of bacteria.
Cold manure (cow, hog manure) has a high water content and ferments slowly.
Hot manure (sheep, poultry, horse) is richer in nitrogen and more easily fermented. These should all be well rotted. There are now sources for goose, chicken and mushroom manure. Check your source to see how it’s produced.
Worm castings are among the most gorgeous-looking and best stuff to use on your soil. They are richer in calcium, potassium and phosphorus than any other organic product.
Rodale’s Encyclopedia of Organic Gardening stresses that it’s pointless to make comparisons between the NKP of synthetic fertilizers and manure. Manure is far more valuable: it provides trace elements not found in the synthetics, as well as organic matter necessary to the life of the soil. Organic matter turns into humus. Humus makes nutrients available to plants.
Fresh animal manure can burn plant roots. It should be well composted to make it safe and to destroy any weed seeds.