Using grass clippings as a liquid fertilizer | Food Production and Preservation | Forums

any of you tried this method?

Here Comes the Science

Fresh grass clippings have a C:N ratio of around 20:1, depending on the species, growing conditions, life stage and time of year. They have an NPK rating of 4 - 0.5 - 2. Lots of nitrogen in there. Used as a compost ingredient, grass clippings can give a heap a tremendous temperature increase.

At Mother Earth News I found an article: Making Your Own Liquid Fertilizer by W.F. Brinton, PhD, founder of Woods End Laboratories. It's a short article but it offers a wealth of information. According to Dr Brinton, the NPK rating of liquid grass clipping tea is 1-.5-3.1. It is also low in sulfates, salts, and sodium.

In his paper Dr Brinton used a ratio of 10 to 1 water to grass clippings by weight. At 8 pounds per gallon of water, a 5 gallon bucket batch would require 4 pounds of clippings. I weighed some loosely packed clippings to find about 1 pound per gallon. For 4 pounds of clippings, a 5 gallon bucket with grass pushed down to the 2/3 level would be consistent with this study.

Comparing to the fresh material suggests there is still a copious amount of N in the leftover clippings. The compost will do well, but with some on the N leached into solution, I would expect reduced heating. In a vermicomposting bin, the advantage is a food source that does not generate as much heat. The relative amount of Potassium surprised me. With such a strong K showing, this liquid should make an excellent contribution to root vegetables. Used early in the growing season, it would promote development of a robust root system, giving the plants greater access to available soil nutrients, minerals, and increased drought tolerance. Used late in the season, it would offer advantages for root and bulb storage as well as for overwintering plants. P is nothing to write home about, but it's a viable source when other sources are few and far between.

Being most folks don't have a laboratory at home, getting the solution diluted to a level where it will not injure plants must be done with a qualitative method. Look to the color and clarity of the solution. If it is dark, dilute it more. If you can't read a newspaper through 6 inches of liquid, dilute it more. When in doubt, dilute it more.

Commercial all-purpose 10-10-10 fertilizer is typically applied at a rate of 10 pounds/1000 sqft. A pint of water is a pound. An equivalent amount of N in liquid grass clipping fertilizer would require 10 times the weight: 100 pounds (100 pints) per 1000 sqft. This works out to 12.5 gallons/1000 sqft or 80 square feet per gallon. Since 1 pound of grass clippings is used to produce 20 pounds, 2.5 gallons, of liquid grass clipping fertilizer, that 1 pound of grass clippings will treat 200 square feet. These numbers suggest a very light application rate is all that is required. Bear in mind, the liquid grass clipping fertilizer is not analogous to commercial 10-10-10. These figures do not line up with the application rate discussed above. Clearly, further experimentation will be needed to determine standard application rates, and these would then be dependent on each growers local conditions.

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