Summer usually means we can start aggressively gardening. For many of us, this is one of the best times of the year. For the next few months, we get to watch our seedlings sprout, grow, blossom, and then comes the best part… harvesting.

While the growing and harvesting part of having a vegetable garden is not only satisfying but also the ultimate goal, it’s important to take a moment to assess how you plant those veggies and what you’re planting them with. Keep in mind that you’ll be consuming whatever is in the soil that your vegetable plant uses as its form of food and energy.

This is where coffee grounds can be a great, natural resource.

Whether you’re a first-time gardener or are extremely seasoned, one thing that never changes is the cost of compost. This is especially true if you’re looking for a high-quality, organic compost mixture that will produce beautiful, safe, healthy, and organic veggies in return. If you’re a coffee-lover, those grounds that you throw out every morning can be saved and used as a nitrogen-rich form of organic fertilizer, mulch, or compost.

Of course, there are special techniques and prep for using coffee grounds correctly and safely. If you haven’t processed your grounds accordingly, the remaining caffeine and high acidity levels can suppress the growth of plants.

So, let’s get down and dirty with this wonderful, environmentally-friendly natural gardening option!

What’s in Coffee Grounds?

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Coffee grounds are the filtered and soaked byproduct of ground coffee beans. Yet, what’s in them? Is there anything left after they’ve been ground, pressed, filtered, soaked, or steamed? The answer is yes! There are quite a few compounds left in this mulchy and aromatic substance. Dried coffee grounds “contain significant amounts of potassium (11.700 mg/kg), magnesium (1,900 mg/kg), and phosphorous (1,800 mg/kg).” They also are acidic, which can give your soil a neutral pH, and provide a slow release of nitrogen into the soil.

How to Compost Your Coffee Grounds

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There’s a bucket in your kitchen and it’s filled with coffee grounds from the past week. Now what? There are a few steps you need to take to make those grounds safe for both the earth and your plants.

While you can put fresh coffee grounds straight into the soil, it’s not recommended. First off, they are highly acidic and quite dense, plus they won’t “immediately add nitrogen to your soil,” as it’s a process that happens as the grounds decompose. This means that, if you’re using fresh coffee grounds that have not been composted, you need to prep your garden bed with the grounds long before you plant your veggies. It’s also important to use only small amounts of coffee grounds if you’re planting seedlings, as the caffeine and acidity can inhibit the growth of these delicate babes! Therefore, in the spring, mix those coffee grounds into the soil, cover them with a tarp for warmth (if you live in a colder climate), and come early summer the grounds will have decomposed and will have begun their slow-release of vital nitrogen.

With that said, the best way to use coffee grounds is to compost them first. Why, you ask?

Turns out that “using coffee grounds alone for mulching could be detrimental.” These tiny grounds are made of “very fine particles that are prone to locking together,” which means they can oftentimes create a “barrier that will resist water penetration and eventually result in plants dying of thirst.”

How do you avoid this? Composting!

After rinsing your fresh grounds, simply mix them “with other organic matter such as compost or leaf mold before using” them in your garden. It’s important to note that these grounds are actually “green material,” which means you need to balance them out with “brown” compost substances including “carbon-rich materials such as dried leaves, woody prunings or newspaper.”

If you don’t have a compost system or if you haven’t planned and you’ve got a pile of fresh coffee grounds waiting to be used, you can also “rake your coffee grounds into the top layer of soil so that they can’t clump together,” or even sprinkle them over preexisting plants in small amounts.

The key is to avoid using coffee grounds on their own — without any other natural soil — and avoid using large quantities.

Benefits of Gardening with Coffee Grounds

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Using coffee grounds is wonderfully beneficial for many reasons. For instance, using them as a fertilizer “adds organic material to the soil, which improves drainage, water retention and aeration in the soil.” On top of that, “the used coffee grounds will also help microorganisms beneficial to plant growth thrive as well as attract earthworms.”

Food for Your Worms

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For seasoned gardeners, you know that worms are your friends. Many gung-ho gardeners have natural worm bins, which are used for vermicomposting. Earthworms have the unique ability to “turn organic waste into extremely high-quality garden soil.” If you have a worm bin, feel free to add a cup or so of coffee grounds every week. Earthworms will love the grounds because they “need gritty food to aid their digestive system which is why the texture of grinds is perfect for them.” For those looking to increase worm activity in their soil, if you use a coffee ground-based fertilizer, “earthworms in your soil will … be attracted to your garden.”

With that said, don’t overdo it! Only use a small amount, a cup or so, as the acidity in them may bother your little worm friends.

Natural Pesticide and Insecticide

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To be honest, there’s a lot of contradicting research regarding using coffee grounds as a natural pesticide or insecticide. With that said, it doesn’t hurt to try it out!

In particular, coffee grounds provide a difficult barrier for slugs to cross. In the journal Nature, a study “found that slugs and snails died after being sprayed with caffeine.” With that said, you don’t have to spray these pests with caffeine to deter them. Simply laying a barrier of thick, very fresh coffee grounds around your most vulnerable plants will oftentimes do the trick. Make sure that you use fresh coffee grounds as the “caffeine needs to be very high (about three times the amount in a regular cup of coffee).”

Reduce Compost-Related Fungal Disease

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Along with being rich in nutrients and acidity, coffee grounds are also anti-microbial. This makes them perfect for fighting off fungal disease that can spring up as your compost composts — organic material that rots into a soil-like substance. Compost-related fungal diseases include “fusarium, pythium, and sclerotinia,” as well as dangerous bugs “like E. Coli and staphylococcus.” Recent studies have shown that coffee grounds can “help to prevent diseases from taking hold.”

Coffee Ground Loving Plants

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You’re ready to get planting with your new coffee ground-based compost. What’s the best thing to plant? If you’ve done your job and composted coffee grounds for a good long while, then you can pretty much use your compost for anything. On the other hand, if you’re using fresh coffee grounds then they will be more acidic. Therefore, you may want to use those grounds for plants that love acidity. Here are a few that seem to do best with fresher coffee grounds.

Vegetables

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If you’re looking to use coffee grounds in your vegetable garden, make sure to only use veggies that are okay with caffeine and acidity and also happen to crave nitrogen. Remember, coffee grounds act as a slow-release nitrogen agent, so you don’t want to use any plants that will be killed off by nitrogen-rich soil. Great plants for a coffee ground-fertilized garden include blueberries, carrots, radishes, “corn, spinach, and any leafy vegetable.”

You can also use coffee grounds for your tomato plants, but there are a few specific rules for this one. Don’t ever use fresh coffee grounds with tomato plants! Tomato plants are thirsty veggies and therefore, using fresh coffee grounds oftentimes starves them of water. Only use well-composted coffee grounds. The high nitrogen is a great food for this fruity plant, so don’t fear using them, just make sure they’ve had a proper chance to decompose!

Flowers and Plants

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Feel free to use your newly minted coffee ground fertilizer, compost, or mulch for flower beds or other non-edible plants. With that said, you need to follow the same rules as you would edible plants. Use your coffee grounds for plants that enjoy nitrogen-rich soil and can stand the acidity levels. These include hydrangeas, “roses, camellias, rhododendrons, and azaleas.”

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