There must be hundreds of articles about using coffee grounds in the garden. I even have one! But the more I read and try these ideas I find that some of these ideas don’t work. At least, they don’t work for me.
Here are my top 5 coffee grounds in the garden myths.
Myth #1 Coffee Grounds Deter Flea Beetles.
For the last five years, I have tried to grow eggplant. However, every year, the flea beetles have destroyed the plants.
If your plant doesn’t have leaves, it will die.
Sure, I have tried covering my plants and rotating their location in the garden, but the flea beetles just show up as uninvited guests.
obsessed gardener who has grown alfalfa, amaranth, and buckwheat, you can’t imagine how hard it is for me to face my eggplant gardening failure. I was ready to just give up until I read a forum suggestion to sprinkle used coffee grounds around the plant and the flea beetles will leave (suitcase and all.)
Since I store my coffee grounds, I decided to give it a whirl. Well, guess what? The flea beetles just laughed at me. It started as a small chuckle and became a collectively belly roll type laugh.
I even tried sprinkling coffee grounds on the plants as well as sprinkling the leaves with coffee grounds diluted water. Nada. Nothing. The beetles thrived and sent me a thank you note.
If this method works for you, I am all ears.
Myth #2 Coffee grounds kill slugs.
Well, they don’t kill or deter my slugs. And no, I don’t have zombie slugs.
Years ago, we had the rain summer from h*ll. The slugs just came out of the woodwork. (Read my slug hunting story here if you need a good laugh.) So, I did my research looking into every possible internet solution from spray coffee grounds on them to setting up a coffee ground line of defense.
The study further states that spraying a caffeine solution of .01% on cabbage plants reduced slug consumption.
Given this study, I applied coffee grounds around my seedlings. Perhaps if I would have continuously sprayed a coffee ground solution, it would have deterred them eating my brassica plants.
Honestly, if you want to try this method, it doesn’t hurt the plant since it is just organic matter. I just won’t rely on it to stop the slugs. It may deter some.
Myth #3 coffee grounds stop aphids.
Two years ago, my tropical hibiscus were covered in aphids and whiteflies. These two pests love this plant along with collard greens and kale. Again, I turned to the gardening forum, and found a comment that aphids hate coffee grounds and will leave.
I put a circle of coffee grounds around the plants.
Again, nada. Nothing. The aphids left me a present. More aphids.
Myth #4 coffee grounds are only good for acidic plants
According to Dr.Hepperly of Rodale Institute, when coffee grounds start to break down, their pH becomes neutral. However, simply throwing coffee grounds around your plants isn’t wise either. Read here how much coffee grounds you should use.
Note certain plants aren’t happy when you use coffee grounds. Linda Chalker-Scott, Ph.D., MasterGardener WSU editor Extension Urban Horticulture, states
“Seed germination of alfalfa (Medicago sativa) and white and red clovers (Trifolium repens and T. pratense)
was inhibited by water leached through coffee grounds. Growth of crops such as Chinese mustard (Brassica juncea), komatsuna (Brassica campestris) and Italian ryegrass (Lolium multiflorum) were all inhibited by coffee grounds, as was that of ornamentals including inch plant (Tradescantia albiflora), geranium, and asparagus fern. One investigator speculated that toxic substances released from decomposing coffee grounds were responsible for their inhibitory effect. This effect also reduces weeds, and perhaps in a landscape dominated by large shrubs and trees, only germinating seeds and seedlings would be injured. But as there has been no experimental research on coffee grounds and woody plants, this is only speculation on my part.”
From own observation, I find that potted plants do not do well with coffee grounds. I don’t know if the coffee grounds cause too much soil compaction so the water cannot percolate through or they just don’t like them. Others swear their potted plants love the grounds.
Just observe . If the plants don’t like it (dropping leaves or looking unhappy) either remove the grounds or just don’t give it to them again.
Myth #5 Add coffee grounds to your compost
Earthworms love coffee grounds. When I added coffee grounds to my compost, the next week you would have thought Mardi Gras came to my composter. There were so many worms crawling throughout my compost.
However, simply dumping endless amounts of coffee grounds into your compost is not a good thing.
Kit Smith, UCCE El Dorado County Master Gardener recommends the compost volume should not contain more than 15 to 20% of coffee grounds. I am guilty of pouring in two huge bags of coffee grounds from Starbucks.
To read more about coffee grounds:
- Coffee Grounds in the Garden: Foe or Friend
- Coffee Grounds and Roses
- How to Get your Coffee Grounds for your Compost just right
Join the Conversation:
- How do you use your coffee grounds?
- Do you have any coffee ground myths to dispel?