I have heard about using coffee grounds in the garden a long time ago. I was reluctant because I thought the grounds were too acidic and did not add much nutritional value.
But I was wrong.
- Coffee grounds have a near neutral pH once they start decomposing.
- They are rich in nitrogen which is good for most plants (not legumes).
- Worms are attracted to them (worms are great for the garden).
- Coffee filters and teabags break down quickly which is great for composting.
- Make coffee ground “tea.” Add two cups of used coffee grounds to a five-gallon bucket of water. Let the “tea” steep for a few hours or overnight. You can use this concoction as a liquid fertilizer for garden and container plants. It also makes a great foliar feed.
Most coffee shops will be glad to give you their used coffee grounds.
Coffee grounds is considered green part of composting (meaning they contain mostly nitrogen. Brown means it contains mostly carbon.) with about 20:1 of nitrogen to carbon.
If you do add a large quantity, you may want to dig them into the garden as there are reports that they will “go bad” and develop a fungal layer if left exposed to the air. They have a carbon-to-nitrogen ratio of 20:1, roughly the same as grass clippings.
Contrary to popular belief, coffee grounds are not acidic. After brewing, the grounds are close to pH neutral, between 6.5 and 6.8. Neutral pH is 7. The acid in the beans is mostly water-soluble, so it leaches into the coffee we drink.
Coffee grounds take a few months to break down.
Coffee grounds are easily compacted which would prevent water and air from reaching the plant, if the coffee grounds layer is too thick (over 1/2 inch).
Coffee grounds lack phosphorus (the key ingredient in flowering fertilizers) so they cannot be used as a standalone fertilizer for flowering plants. If you could buy coffee grounds in bags at garden centers the 3 numbers on the bag would be 2-0.33-1. (nitrogen – phosphorus – potassium)
Conclusion
Don’t use coffee grounds as an only mulch. Sprinkle up to 1/2 inch around then cover with a few inches of coarse mulch, such as wood chips.
Use 10% to 20% volume in a compost pile.
Work coffee grounds into the soil so they do not mold. It is best to compost coffee grounds before using them.
I put some around some vegetables and roses which I’ll report on at the end of the growing season.
Update
Although empirical, I notice a lot more worms in the garden this year. Could be the coffee grounds…