Garden DIY articles often advise mixing coffee grounds into your soil and compost. It seems like a good idea because it recycles used coffee grounds and gives your plants some free food, but what is it actually doing to the soil? While coffee is good for you, the jury is still out on if coffee benefits your plants. Coffee grounds are rich in nitrogen, which is essential for plant growth, but they also contain a high concentration of caffeine and acid, which can be detrimental for some plants.1 We’ll break down the risks and benefits of using coffee grounds on your flowers to help you decide if you want to give the grounds a go.
Why Coffee May Help Your Soil
Rich in nitrogen and loaded with antioxidants, coffee is good for humans to drink in moderation because it helps our body regulate inflammatory responses and process glucose, which may lower your risk of type 2 diabetes. Nitrogen is an essential element in plant growth and a key nutrient in fertilizer, so coffee grounds may help give your plants some free vitamins.
Why Coffee May Not Be the Best Choice
Ground-breaking news: coffee contains high levels of caffeine and is very acidic with a pH range of around 4.8-5.10. These are two elements that most plants and their soil don’t take too keenly, but it may not be as big of a deal depending on the plant. For example, blueberry bushes and Christmas Cactus actually like fairly acidic soil, so this is good news for them.
If your grounds are processed in well-balanced, mature compost the acidity also may not be as big of a deal for any plant because the pH has been balanced with “wet” and “dry” components such as vegetable peelings and sticks. However, what’s more uncertain—and more concerning—is the fact that certain studies have shown caffeine may kill your plants.
At first, all seems well because the plants typically experience a short burst of accelerated growth, but it seems that they usually turn brown and die shortly afterward. Researchers aren’t sure how much the individual plant or plant species may be responsible for this, but they speculate that the caffeine does indeed have some lethal power because the coffee plant will kill competing plants in the wild. More research needs to be done however before we can say specifically if it affects all plants or only some.
It’s up to you whether you want to give your grounds an extra shot. If you’re worried about the acidity, you can make sure the compost is well-balanced or just use it on plants that thrive on acidic soil. The caffeine is a little more questionable but might be fine in low amounts. The risk is obviously less if you use decaf grounds, so if you’re a caffeine addict, ask a neighbor who drinks decaf if they might be willing to share their used grounds with you. And give them a tomato or two in gratitude.
Featured Image Credit: Marco Taliani de Marchio, Shutterstock