Issue: September 26
Coffee grounds and tea leaves are good for New Mexico gardens
Q. Can I put my used coffee grounds and tea leaves in my garden? I was told that they will make my soil too acid and I wondered if the caffeine will hurt my plants.
T or C area
A. Yes, you can put both coffee grounds (with paper filters) and tea leaves (and paper tea bags, not polyester bags) into the garden or the compost pile. In most of (or all) New Mexico, you will not be able to make the soil too acidic by adding coffee grounds and tea leaves. They add organic matter to the soil to help hold moisture and nutrients for the plants. Organic matter slowly decomposes releasing even more nutrients at a slow rate so that plants are less likely to be burned or over fertilized as can happen with commercial fertilizers. Organic matter helps optimize the soil structure, increasing drainage and soil oxygen levels (necessary for good root functioning) while also increasing the moisture available to plants.
Coffee grounds and tea leaves can be added directly to the soil or placed on the surface around the plants (bury filters and tea bags since they are unsightly). If they are placed on the surface, they will decompose more slowly. They serve as mulch around the plants, conserving soil moisture, and making it easier to pull weeds around the plants if you are vigilant and do not let the weeds develop deep roots. Organic matter, especially coffee and tea, are attractive to native earthworms that will help release the nutrients from the coffee and tea and, at the same time, increase the soils ability to allow permeation of water and air.
Compost piles can also benefit from coffee and tea. They are good for encouraging the growth of decomposing bacteria and fungi that will also decompose the other waste material in the compost pile. The end result will be better compost which will help improve your garden soil.
You can add coffee and tea to the garden any time of the year which is good because you have supplies of coffee and tea most of the year if you drink coffee and tea daily. During the summer while plants are growing, you can apply these materials as mulch or to the compost pile. When the garden is inactive, they may be mixed directly into the garden soil.
Although I mentioned that nutrients are provided by coffee, tea, and other decomposing organic matter, it is wise to have your soil tested periodically to determine if other nutrients are needed by the plants you will grow. You may still need to add additional nutrients based on the results of the soil test.
Regarding the caffeine in coffee grounds and tea leaves, it is unlikely to harm your plants. The caffeine molecule is probably not absorbed by the roots of plants. It must be decomposed by bacteria and fungi to release the component elements in coffee before they can be absorbed.
For more gardening information, visit the NMSU Extension publications World Wide Web site at http://aces.nmsu.edu/pubs/_h.
Send your gardening questions to:
Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd. SW
Los Lunas, NM 87031
Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.