1 - Coffee grounds is a beneficial source of organic matter for your garden, but like some other fine textured organic materials there is a chance that they will cause a temporary depletion of plant available nitrogen while they are decomposing.

Yard and Garden June 28, 2014

Q.

I have heard that coffee grounds are good fertilizer for my garden, and then I read that they deplete the nutrients in my garden. Is it safe to dispose of my spent coffee grounds in my vegetable garden?

A.

Coffee grounds and other kitchen wastes are useful in your garden, but there are misconceptions about them. I checked the internet to see what you referred to and discovered several articles saying to use coffee grounds as fertilizer because they contain nitrogen and other articles saying that the organisms that decompose the coffee grounds will deplete the nitrogen in the soil, causing nutrient deficiencies in garden plants.

The nitrogen in coffee grounds will be released to the soil after they have decomposed, but the potential problem occurs during the decomposition process. That is when the bacteria and fungi that decompose organic matter will be using nitrogen to reproduce and grow. They can indeed reduce the nitrogen available to plants. Addition of some nitrogen fertilizer when adding coffee grounds to the soil will alleviate this problem. If small quantities of coffee grounds are distributed over a large area of the garden soil, there may be little effect on plants even if you do not add additional nitrogen. Of course, the benefits of the coffee grounds are diluted as well. It is when greater quantities of coffee grounds are used in small areas that nitrogen depletion may become a problem.

A simple solution often mentioned in the internet articles is to add coffee grounds to a compost pile with other kitchen and garden wastes. Then the organisms decomposing the coffee grounds and other organic wastes will use the nitrogen in the compost pile where they are not competing with garden plants. After the organic wastes have decomposed and the organisms that caused the decomposition have died, the nitrogen used by those organisms can now be released to plants in the garden.

Coffee grounds are a useful amendment to garden soils if care is taken to avoid competition with garden plants for nitrogen. Coffee grounds are also beneficial amendments to your compost pile and the finished compost is beneficial in your vegetable garden. The organic matter adds slowly released nutrients, increases water-holding and nutrient-holding capacity of your garden soil. Your plants should respond positively. The organic matter adds slowly released nutrients, increases water-holding and nutrient-holding capacity of your garden soil. Your plants should respond positively.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

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