Saving Used Coffee Grounds for Gardening

photo by Steven DePolo

Why coffee grounds? How can they enhance the growth and well-being of plants? Isn't coffee too acidic for the soil? Used coffee grounds are in fact an excellent organic material for gardening. They are a rich source of nitrogen. This element feeds beneficial microbes which break down other organic matter, and supplies nutrition to plants. They make a safe, natural substitute to manure for compost piles, as they are approximately two percent nitrogen by volume.

Researchers have also found that the presence of the grounds in compost piles helps sustain higher temperatures. These temperatures are ideal for preventing potentially harmful pathogens and kill seeds from surviving. Old coffee grounds have also been shown to improve soil structure and attract earthworms. As most of the acids are leeched out into your cup of coffee while brewing, the grounds are actually close to neutral, with an average pH ranging from 6.5 to 6.8. With a knowledge of proper use, used grounds are an ideal substance for growing better plants.

To use coffee grounds effectively they must be broken down before being placed around plants. Before composting, they have a carbon to nitrogen ratio of twenty to one, which is about the same as animal manure. In this state they can potentially stunt the growth of plants. Composting transforms the grounds into a beneficial source of nitrogen.

How to compost the used grounds? One easy way is to spread them on the top of soil weeks or months before planting, and cover with a layer of leaves or bulk mulch. You can also simply toss the used coffee grounds into your existing compost pile. This will allow the material to break down over time. It can then be mixed into the soil as a nitrogen fertilizer or added to houseplants.

Not only are used coffee grounds great for gardening, but this practical use is good for the environment as well. Coffee grounds are thrown away, eventually ending up in landfills. As they decompose in the waste stream they actually contribute to greenhouse gas emissions by emitting methane. While your daily consumption of coffee may not be that high, the amount of coffee grounds thrown away every day by coffee shops is enormous. By making connections with local cafés, asking for their used grounds, you are supplying yourself with free, natural fertilizer and reducing waste and greenhouse has emissions.