- Coffee grounds contain 2.0 percent nitrogen, 0.36 percent phosphorus and 0.67 percent potassium. Analysis of coffee grounds has shown that they also contain calcium, magnesium, sulfur, boron, copper, iron, manganese, zinc and other trace minerals. Coffee grounds are particularly effective for plants that prefer an acidic soil, such as roses, blueberries, evergreens and some fruit trees.
Freshly Dried Grounds
- Acquire fresh coffee grounds directly from your coffee machine, or source them from a neighborhood cafe or the coffee machine at your office. Dry the grounds in the oven, as damp coffee grounds can become moldy rapidly. Scatter them lightly around the plants that will benefit from them.
- Coffee grounds make an excellent mulch. To build up the acidic content of your soil and to benefit a large area, simply tip the coffee beans into the garden and dig the soil over. Coffee grounds are dark in color and will absorb the sun, helping the soil to warm up and adding nutrients as they break down into it.
- To make an effective liquid garden amendment, you can mix a pound of coffee grounds into a bucket with 5 gallons of water and leave it to warm up in the sun. This will provide a nitrogen-rich liquid feed for the plants. Take care not to use this on plants that prefer an alkaline environment, as they may not thrive on it. You can also simply pour cold, diluted coffee onto the plants, provided it does not contain milk or cream.
Mix with Compost
- Coffee grounds are a welcome addition to a compost heap. This will add a strong dose of nitrogen to the compost, since the carbon to nitrogen ratio is around 20:1. If you are using a worm composter, the worms will happily receive and process coffee grounds.
- Coffee grounds are a pet and pest repellent as well as food for the plants. Dogs and cats appear to dislike the bitter coffee smell, and this causes them to stay away from plants with grounds spread around them. Coffee grounds also repel slugs and snails, keeping your plants safe from these pests.