Used coffee grounds can provide your garden with helpful nutrients when properly composted. They are a good source of nitrogen, are green compost materials, and have been said to repel slugs. Fresh coffee grounds on the other hand are acidic and can be harmful to many plants.
Once you’ve made your coffee you have the undesirable task of cleaning up the grounds. Instead of just throwing the coffee grounds out, you can add them to your compost bin to benefit your garden soil and plants later.
In this article, I’ll cover the benefits of coffee ground to your plants, and I will explain exactly when you shouldn’t use it.
What do Coffee Grounds do for Garden Soil?
The benefits of coffee grounds in a garden have been debated and studied for years. One benefit is to your garden soil. You can use coffee grounds in your garden as mulch. This provides a number of benefits including better water retention, soil structure, and weed control.
The improved water retention can be good when the plants enjoy moist soil. If the plant prefers dryer soil you may be stressing them by improving the water retention.
However, this is only the case when used correctly. Since the grounds are so fine, they can easily pack together and prevent water from entering the soil. To prevent this you can either use the grounds in your compost or spread them out evenly.
Lastly, unless you are growing plants that like acidic soil don’t use fresh coffee grounds. Used coffee grounds are much less acidic, around 6.5 to 6.8 pH. These used grounds will be much more neutral towards your plants.
What can Coffee Grounds do for Plants?
While the benefits for the soil are great they aren’t the only ones. Coffee grounds can also be good for certain plants. Azaleas, blueberries, hydrangeas, and radishes all prefer slightly acidic soil. These plants would enjoy the acidity brought by fresh grounds while others would not.
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Plants that like coffee grounds |
Plants that don’t like coffee grounds |
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Carrots |
Tomatoes |
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Rhododendrons |
Lavender |
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Cabbage |
Lilac |
That said, coffee grounds aren’t all rainbows and sunshine. Even when used near acid-loving plants they can have a negative impact on freshly planted seeds. Coffee grounds can inhibit the early growth of seeds. They do this by reducing root growth, effectively stunting the plant.
Once the grounds break down they can help established plants continue to grow. As mentioned above, coffee grounds contain nitrogen–up to 2% by volume. Adding nitrogen to your garden soil will help your plants grow healthy.
So not everything that coffee grounds do is helpful for plants. Just make sure you know the requirements of your plants.
What About Potted Plants?
If you don’t have a garden but still want to make use of your grounds you are in luck! The same benefits and principles as above apply to indoor plants. You still need to keep the needs of the plant in mind.
If using fresh grounds make sure the plant likes acidic soil. Don’t let the grounds form clumps or barriers that will prevent water from reaching the plant. For the most part, you won’t have an issue if you compost it first.
Additionally, you will need to use a small number of coffee grounds per pot. Unless you have very large pots you will not need much.
How to Use Coffee Grounds to Their Full Potential
Naturally, this isn’t as simple as just sprinkling your used coffee grounds around your plants. While you can do this, you will benefit from preparing the grounds first.
In order to get the most out of them, it helps to compost them first. The nitrogen that is in coffee grounds doesn’t get released into the soil right away. It usually takes a few months for the grounds to sufficiently break down.
Coffee grounds are a green material when it comes to composting. When you add the grounds to your compost bin make sure they don’t make up more than 20% of your green compost materials. Be sure to follow the 1:3 ratio of green to brown compost materials.
In addition to the grounds, you can also add a paper coffee filter. If you tear it up you can speed up the composting process.
