Don't Toss Coffee Grounds Into Your Compost Pile Without Knowing This

Coffee grounds are beneficial to add to compost piles since they contain nitrogen, and they're a big hit with worms if you vermicompost. Adding them to your compost pile is one unexpected use for leftover coffee grounds around your home. Keep in mind that letting your grounds decompose is an important step when using them to fertilize your plants – this is why adding them to your compost and not directly into your soil is ideal. Also know that there can sometimes be too much of a good thing. Before you dump lots of coffee grounds into your compost pile, it's important to know that you need to use moderation. If your mixture is made up of more than 20% grounds, you may be in for problems like odors, sliminess, and too much caffeine, which could harm plants.

In order to reap all of the benefits of composting at home, you need to mix the coffee grounds with plenty of other organic materials. Coffee grounds are considered a green additive to your pile. As long as you layer them and other greens (like kitchen scraps) with plenty of browns (like twigs, paper, and leaves), the dregs from your morning brew will definitely still have a helpful role to play in your compost. 

Nitrogen seems like magic for all things gardening. In a compost pile, it's the greens that provide this much needed element. Despite their actual brown color, coffee grounds are considered a green material. The general recommendation is to layer carbon-providing brown materials with green ones. The ideal brown to green ratio is around 30:1. As hungry microscopic creatures go to town on the pile's bits and pieces, they prep this nitrogen for plants to use.

However, the high levels of nitrogen that coffee grounds provide can lead to smelly results. If your pile is giving off an ammonia or rotten egg odor, that can be a sign that you've got to bring in some browns. Another sign that your pile has a coffee overload is a slimy or wet look on its contents. This isn't ideal, as this shows that the pile probably isn't being properly aerated or decomposing correctly.

Adding too many coffee grounds could also include too much caffeine in your pile, which could harm plants. A 2020 study published by the BIO Web of Conferences found that too much caffeine can slow down the growth of plant tissues and roots, so if you tried to grow any plants in the compost, you might run into some problems. Fortunately, mixing in more browns like layers of shredded paper can tackle all of these issues. Also monitor how many coffee grounds you include in the pile to keep the ratio between green and brown materials balanced.