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Because You Asked: How Can I Use Coffee Grounds as Fertilizer?

Written by Recyclebank .

Coffee grounds definitely should go back in the ground, but what about potted plants?

Dear Recyclebank,

I tried adding used coffee grounds to my house plants and had a mold issue. What did I do wrong? Also, can I use the actual coffee as fertilizer?

-Dawn R., Madison, WI

Coffee grounds are an excellent addition to compost piles and outdoor gardens, but they can be tricky when it comes to indoor container gardening. When mold appears on grounds in a compost pile, it is eventually consumed by bacteria and turned into compost — no big deal. In an indoor setting, mold is unsightly and can pose hazards to human health. Fortunately, there are a few strategies you can take to successfully add grounds to your indoor plants.

  • Reduce the amount and/or frequency of watering. A common reason for mold appearing on potted soil is excessive moisture. You may want to let the soil dry out a bit before adding grounds, especially if the grounds are already damp.
  • If applying to the surface of the soil, layer the grounds thinly. Grounds can be compacted, retaining moisture and preventing aeration. This can result in an ideal environment for mold growth.
  • Try mixing the grounds in with the top layer of soil. The variable particle size helps prevent compaction, thus improving drainage.

As for using the coffee itself as fertilizer, there seems to be little scientific evidence confirming its benefits but plenty of anecdotal evidence in the positive. Coffee is rather acidic, which can be beneficial to plants that thrive in acidic soil. However, it’s probably still a good idea to dilute any coffee you’re adding.

Oregon State University Extension Service
University of Illinois Extension

Do you add coffee grounds to the soil of your houseplants? Tell us if you’ve found success in doing so!

Share this with Your Friends
  • Sue C. 5 months ago
    This is good to know that coffee grounds can be beneficial to plants that thrive on acidic soil as well as being able to be added to a compost pile. Another great way to reduce waste. thank you.
  • Bridget C. 6 months ago
    I always put my coffee grounds in my garden, but not on inside house plants because of the mold. :)
  • Julie M. 6 months ago
    I've been wanting to start a compost pile ( we have the perfect place in the yard ) and this has given me the spark to get on it. We have someone mow our grass, so I can have him leave the clippings, and I use coffee grounds in my knockout roses-they love them!
  • Glenda M. 6 months ago
    We compose everything we can and the garden dirt is so rich and beautiful. It is a great way to enhance the use of the earth's soil.
  • Robert M. 6 months ago
    I collect the coffee grounds from our local donut shop and use them in my compose bin and flower garden.
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