Why coffee grounds are good for your garden

The key is to have variable particle sizes in your soil and mulch to promote good soil structure. Coffee grounds contain several essential nutrients such as nitrogen, potassium, and phosphorus, along with micronutrients — all of which make using coffee grounds for plant mulch a great idea. The amount of nutrients in each batch of coffee grounds varies, but ultimately, coffee grounds can be used as a slow-release fertilizer. Sprinkle coffee grounds in a thin layer onto your soil to use as a fertilizer.

Another plus? Worms like coffee grounds and worms are a necessary part of the ecosystem that is any garden. Composting can be very beneficial. There are two types of compost material: green and brown. Coffee grounds fall into the green category since they are a green material, which means they are rich in nitrogen. Coffee grounds typically have about 1. Other green materials are food scraps and grass clippings.

All of these green materials contain magnesium, calcium, potassium, and other trace minerals. You can throw your coffee grounds, paper filter and all, into your green compost bin, but when it comes time to put the compost in the garden, you must mix your green compost with some brown compost.

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New comments are only accepted for 3 days from the date of publication. Easy, delicious dishes. Kitchen Cabinet Tops chefs share favourite recipes. Sign up. Advertising Feature. Subscriber Only. Three of the best pizzas in Ireland, and where to eat them. Three of the best steaks in Ireland, and where to eat them. We grew up eating avocados. Baked vanilla cheesecake. A special autumn salad. Unless you plan on measuring the acidity of your coffee grounds, amending your soil with them may do little good for your acid-loving plants and little harm to your alkaline-loving plants.

Despite common lore, coffee will not stunt your growth. But it can stunt your plants' growth. Research published in Urban Forestry and Urban Greening determined that the direct application of spent coffee grounds on soil significantly reduces plant growth.

One of the main culprits: caffeine. Even after brewing, levels of caffeine remain in coffee grounds that are high enough to negatively effect seed germination and early plant growth. From an evolutionary perspective, this makes sense; for the same reason that acorns are acidic, coffee beans release toxins in order to inhibit the growth of competitors.

Those same toxins can also inhibit the microbial activity that makes nutrients available to plants and can deter earthworms and other underground digesters. Just as running the same grounds through your espresso maker produces a weaker cup of coffee, over time the phytotoxicity of coffee grounds declines and their benefits increase. As the grounds mineralize, they release essential macronutrients to the soil, which attracts microbiota that, in turn, make those nutrients available to plants.

Indeed, research published in Applied Soil Ecology found a direct correlation between increased application of spent coffee grounds, leached of their toxins, and the abundance of beneficial soil fungi and bacteria that promote plant growth. Another study found that as the toxicity level of spent coffee grounds decreased, earthworm activity increased, with no apparent detrimental effect on earthworm health.

Before you start adding coffee grounds to your soil, you might want to get your soil tested to see what it actually needs. Most garden centers sell simple pH test kits. The extension service of your state university should also be able to provide a more comprehensive determination of the amount of essential minerals in your soil. Grab a moist handful of your garden soil and squeeze it in your fist. If the clump immediately falls apart, your soil is too sandy.

Good soil will hold its shape, but crumble if you start poking at it. If it doesn't crumble at all, your soil is has too much clay. Depending on the results of these tests, you may want to add more or less coffee grounds to your compost or mulch. Be wise in what you do with your coffee grounds. Using them as a mulch directly on your soil can inhibit water retention and air circulation, and have a negative effect on plant germination and early growth. But the indirect use of coffee grounds can have just the opposite effect.

Adding a modest amount of coffee grounds to your mulch or compost pile can improve your soil.