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coffee outside garden table

Coffee grounds are full of nutrients that are beneficial to your garden. Turn your cuppa joe into a key ingredient for outdoor greenery. Here’s how.

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I’ve been composting my coffee grounds for years, right along with the filters. Coffee is a plant product, and paper is not bad in the compost pile, so they always seemed like a natural addition. When a friend asked me if I wanted some grounds from her coffee shop, I naturally said yes. I didn’t fully realize how beneficial they are in the compost pile and in the garden.

Minerals in the garden

Coffee is acidic, but because the acid is water soluble, it is brewed out. You drink it. Grounds are close to neutral or slightly acidic on the pH scale, ranging from 6.2-6.7. This is preferable for most plants, so it is somewhat of a myth that spreading coffee grounds around the base of acid-loving plants will help them.

Grounds are also high in nitrogen, but it is not available to plants right away. As the grounds break down, nitrogen is released, and the grounds become a slow-release fertilizer. Heavy nitrogen feeders, such as leafy greens, corn, tomatoes, and squashes, benefit from this action over the growing season. You have to use a fast-acting nitrogen fertilizer when planting and getting the seedlings growing initially.

coffee grounds in bowl

Coffee grounds also contain phosphorus, potassium, magnesium, copper, calcium, zinc, manganese and iron, important minerals for plant growth. Again, they are not immediately available, but will be released as the grounds biodegrade.

As a soil conditioner

Coffee is a plant material high in what we call ‘organic matter’. Just like adding finished compost to your garden beds, adding coffee grounds benefits the texture and structure of the soil. They help aerate the soil for better drainage and water retention. That sounds like a paradox, but tiny air spaces are created by the texture of something like coffee grounds, and they hold water while letting it move freely through the soil.

The nitrogen in the coffee grounds is yummy food for micro-organisms, which help break it down, which releases more nitrogen to your plants. So the grounds attract these beneficial organisms. Worms like them, too! If you have a worm bin, be sure to add coffee grounds to it weekly along with other foods.

Grounds make good mulch, which protects the soil from the elements. Spread at a thickness of about ½”, and cover them with regular mulch. Otherwise they will dry out and make a sort of mat, preventing water and air getting to the roots of the plants.

garden gardening gloves spade soil

Pests

Some gardeners report that putting a thin layer of grounds around the garden deters slugs. I can’t imagine a slug would be very comfortable trying to slither across them! It is also said that they will deter rabbits and squirrels from spring crops.

Coffee grounds have antimicrobial properties, so they will suppress fungal diseases. They should be added to plantings of cucumbers, beans, tomatoes, eggplant and peppers to help reduce diseases such as fusarium and pythium.

Compost

If you think about all these qualities of coffee grounds, it’s easy to see why they would make good compost! The high nitrogen content makes coffee a ‘green’ component of compost. That’s the part that heats up the pile and breaks down the ‘brown’, or carbon, part of the pile. Dried leaves, sawdust, corn stalks and wood chips are considered brown. Grass clipping, weeds, and kitchen scraps (living things) are considered green.

Grounds and green matter should constitute no more than 25% of the pile by volume. If you have too much green matter, the pile smells like garbage. If you have too little, the pile never heats up to decompose. Green and brown, or nitrogen and carbon, have to be properly balanced to make good compost. Carbon : nitrogen (C:N) = 4:1.

Drink up!

As you can see, there are many good reasons to add coffee grounds to your garden and compost pile. So drink up!

Also hit up your local coffee shops for bulk grounds. You can provide them a bucket or two, but they are usually already dumping them into a bucket that is separate from their trash.

You will do the shop owners a favor by recycling their coffee grounds. If the grounds did not go into your garden, they would go to the dump. Considering how trendy coffee is today, that’s a lot of garbage. Save a landfill, and grow a lush, colorful and fragrant garden instead!

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Nan Fischer

Nan Fischer has been living and building green for over 35 years. Nan’s emphasis on the BuildDirect blog is about how to make your dollar stretch further, while also moving toward a more sustainable lifestyle, as well as upcoming and existing technology to help us live in an ecologically-friendly way. Nan also authors posts on the website of her seed business, sweetly seeds.