3 Ways To (Properly) Use Coffee Grounds In The Garden
Are you one of the ~50% of Americans who drink coffee daily? Chances are, the grounds used to brew that coffee go to waste. But what if they could serve a 2nd purpose in your own garden instead of going to the landfill?
There is a lot of false information out there about gardening with coffee grounds. In this article, I’ll share 3 ways to use coffee grounds in the garden properly. With these simple methods, you can give your garden a boost with your morning beverage leftovers. Let’s get started!
1. Compost Them
By far the best way to use coffee grounds in the garden is to compost them. Coffee beans are dead plant material, so they make a great addition to the compost pile. Coffee grounds are considered nitrogen-rich, so they qualify as a “green” material.
So, why compost the coffee grounds before applying them in the garden? The reason is that spent coffee grounds contain nitrogen and other nutrients, but they are not readily available for plant use. If you apply the grounds directly to your garden soil, the plants won’t be able to use the nutrients to grow.
To make the nutrients available for plant growth, they must be broken down into simpler molecules, first. And the best way to do this quickly is with a compost pile. If you have never composted before, you can get started with a few simple, free ingredients. For example, you can start with just coffee grounds and dried leaves. You can also add in some fresh lawn clippings, garden waste, or kitchen scraps.
To have a successful compost pile, it needs to be large enough. At minimum, you should form a pile that is 3x3x3 feet. The ratio of “greens” to “browns” is also important to speed up the break down process. In general, I use a 3 to 1 ratio of browns to greens respectively. Learn more here.
Tip: Compost the coffee grounds and the coffee filter. Filters are paper-based, making them an excellent brown material for your compost pile.
2. Slug Deterrent
Another possible use for your coffee grounds in the garden is as a slug and snail deterrent. Caffeine is known to be poisonous to slugs and snails. Since coffee has such a high concentration of caffeine, we can use the grounds to our advantage against these garden pests.
However, just sprinkling the coffee grounds around your plants likely won’t be enough to deter them. The concentration of caffeine needs to be high enough to become toxic to the slugs and snails.
Here’s how to use coffee as a slug deterrent:
- Brew strong coffee and allow to cool
- Dilute the coffee with water to a 2:1 ratio (2 parts strong coffee, 1 part water)
- Drench the soil with the solution around affected plants
While this is the best way to use coffee as a slug killer, it doesn’t have to be perfect. You can still use spent coffee grounds to brew a soil drench. however, I would not suggest diluting the solution with water if the grounds have already been brewed. Simply allow your spent coffee grounds to steep in water overnight, then use the strained solution to drench the soil.
According to Oregon State University, a coffee soil soak should kill slugs and snails if the caffeine concentration is high enough. While this isn’t a perfect science (all coffees have different caffeine levels), it may be worth a shot if you’re dealing with slugs or snails!
3. Use Them As Mulch (Carefully)
If you have an abundance of coffee grounds, you may have enough to use them as a weed-suppressing mulch. While they wouldn’t be my first choice (I prefer dried leaves or straw), it may be a good option for you.
The best mulches are natural (check), allow water to penetrate (check), and slowly add nutrients to the soil over time (check). Not only does coffee check all of these boxes, but it is endlessly available for free from your local cafes.
This makes it a great choice if you live somewhere you can’t gather fallen leaves or grass clippings. In a city setting, spent grounds could be the cheapest option for a natural mulch.
However, be warned that coffee grounds may cause some issues as a top dressing if not carefully monitored.
Potential issues when using coffee grounds as mulch:
- Coffee grounds may dry out and repel water. To avoid this, mix a bit of dried leaves or straw into the grounds before applying as a mulch.
- If coffee grounds are worked into the soil, they can tie up nitrogen as microbes break them down. Avoid working the grounds into the soil (it is not an amendment!), or apply a nitrogen fertilizer to compensate.
How Not To Use Coffee Grounds
Now that I’ve covered the best ways to put your spent coffee grounds to use, let’s talk about what not to do with them. Coffee grounds clearly have a place in the garden, but they can also cause damage.
- Don’t work it into the soil. Coffee grounds are not a substitute for fertilizer. In fact, when they are used as a soil amendment, they can significantly reduce plant growth in a variety of soil types and crops. This is likely due to soil microbes using nitrogen to break down the coffee grounds, stealing it from nearby plant roots. Always compost coffee grounds, first!
- Don’t bother trying to acidify soil. If your soil is highly alkaline, you may need to adjust the pH. Coffee grounds are acidic, but they cannot significantly reduce pH. Instead, sulfur can be used to have a much more dramatic effect on acidifying soil.
While I wouldn’t recommend using coffee grounds in these ways, your garden is yours to enjoy! If you want to add coffee grounds to your garden and compare results, that is your choice to make. Perhaps the results will be pleasantly surprising.
I hope this article helps you put your used coffee grounds to use in the garden! There is no need to throw away coffee grounds when they can add benefits to your fruit and vegetable plants. Good luck!
