There is a lot of information on the web regarding the use of used coffee grounds and gardening. I am hoping you can answer the questions below:
1. can i put my used coffee grinds in my “cold” garden compost bins? We have about 1/2 cup of used coffee grounds per day.
2. will sprinkling the used coffee grounds around plants that slugs/snails like limit their visits to those plants?
3. are there any garden perennials that absolutely should not have used coffee grounds around them?
4. are the used coffee grounds good or bad for the worms if sprinkled directly on the garden?
Thanks for contacting the Toronto Master Gardeners.
As you note, there is a lot of information on the web about the use of coffee grounds and gardening–sometimes difficult to discern fact from fiction.
- Yes, you can put used coffee grounds into your “cold” garden compost bins; it’s best to mix them into the compost as sometimes the grounds can clump.
- Sprinkling used coffee grounds around plants that slugs/snails like has no effect on them; there have been studies that show that caffeine will kill slugs; however, coffee grounds contain very little, if any caffeine; slugs are not affected by coffee grounds at all.
- There is little evidence that coffee grounds have a negative effect on established garden perennials; some studies have found that soil amended with coffee grounds may affect seedlings in the short term; “in the long run they improve plant growth”. [Robert Pavlis: https://www.gardenmyths.com/coffee-grounds-garden-safe/]
- Used coffee grounds, when sprinkled directly on the garden, seem to have no effect on the worms, as long as the grounds are mixed into the soil. However, it’s best if they are composted first.
Hope that these answers will alleviate any concerns you have about using your coffee grounds in the garden. If you have any other questions about the use of coffee grounds in the garden, please check the references listed below.
The following article is by a leading researcher who writes about garden myths. She goes over the fact and fiction of coffee grounds in this article.