When I was visiting my parents recently, I helped them compost some of their food waste. The biggest one? Coffee. Every morning they would make a BIG pot of coffee and had lots of grounds as a result. After hearing about it online, I told them they should add it to the soil around their citrus trees. But was I right? Are coffee grounds good for citrus trees? I did some research to find out more. Here’s what I found.
While coffee grounds can help citrus trees by adding acidity and nitrogen, there are some concerns about the residual caffeine. Since caffeine can kill beneficial bacteria and insects, it’s best to let coffee grounds break down in a compost pile first before applying it to the soil around citrus trees or other plants.
So, while there are concerns that using too many coffee grounds can harm beneficial life in the soil, how exactly should you process them and how much should you apply? Let’s explore a bit more.
How Do Coffee Grounds Help Citrus Trees?
Depending on how you use them, coffee grounds can bring several benefits to the soil around your citrus trees.
Coffee grounds contain a good amount of nitrogen, phosphorus, magnesium, and copper, all of which are important to maintain a healthy plant. They also increase the acidity of the soil, which is helpful for citrus trees as they prefer more acidic soil with a pH of 6.0-7.0.
But while there are some advantages to using coffee grounds, there are also some disadvantages.
Do Coffee Grounds Hurt Citrus Trees?
Earlier, we mentioned that caffeine can kill beneficial life in the soil. Let’s take a further look into why this is the case.
Caffeine is a natural defense mechanism from plants to repel insects. This means it’s a type of insecticide, which is bad news for worms and pollinating insects. However, the science is debated as some believe the caffeine is gone after brewing, while others say that there is plenty of caffeine left in the grounds.
Since most of us can’t or won’t regularly test the microbes in our soil or the impact on insects, it’s best to take the safe route on this one. Let the coffee grounds decompose in a compost pile first before applying it to your garden or citrus trees. If you have worms in your compost pile, consider skipping the coffee grounds and try scattering them in your garden to reduce the caffeine’s potency.
How to Apply Coffee Grounds As Citrus Tree Fertilizer
Since coffee grounds can have a lot of leftover caffeine, it’s best to let it sit in the compost pile first. But what if you just have a small amount of grounds? And how long might it take for the caffeine to break down?
You can apply a small amount of coffee grounds directly to your garden’s soil. However, if you’re consistently dumping 2 or more cups of used coffee grounds, consider composting it first to reduce the level of caffeine. It takes about 2-3 months for the coffee grounds to break down and become usable as nutrients.
It can take some time for the beneficial microbes, worms, and insects to build up in your soil, so avoiding a large dose of deadly caffeine is a smart move. For more about worms, including the best ones to use in worm bins, you can check out my recent post: The 6 Best Worms for Composting.
If you do apply a small amount of coffee grounds directly to your citrus tree’s soil, you should scatter it within the drip line of the tree, but not too close to the trunk. A good rule is to stay about 12 inches away from the trunk and then cover the coffee grounds with 1-2 inches of soil. This will also help prevent the grounds from developing mold.
When a small quantity of coffee grounds are mixed into the soil like this, the level of caffeine is weakened and shouldn’t be harmful. If you’d like, you can provide the soil with a deep watering, which will help leech away some of the residual caffeine.
If you’re looking for more information about reviving nutrients in your citrus tree’s soil, I made a short guide that breaks down all of the information, along with two products that I use at home for my citrus trees.
How Many Coffee Grounds Should You Use on Citrus Trees?
If you’re using coffee grounds with other ingredients as compost or fertilizer for your citrus tree, try to keep the coffee grounds below 15% of total soil content.
Try not to use too much coffee grounds on a potted citrus tree. The limited amount of soil it has to work with can be overpowered with the nitrogen and residual caffeine from the coffee grounds.
Even though the coffee grounds can help with important nutrients and provide a slightly acidic pH, you still want the majority of your compost to be composed of leafy greens or other carbon-rich vegetation.
For more about how food scraps can benefit your citrus trees, check out my post on crafting your own homemade citrus fertilizer.
When Should You Apply Coffee Grounds to Your Citrus Trees?
If you’re composting your coffee grounds for your citrus trees, the best time to add it to the pile is in the winter. After 2-3 months, the compost will be ready to use in the spring, which is when citrus trees prefer to be fertilized. However, if you’re applying the grounds directly to the soil, any season will work.
If you have larger amounts of coffee grounds, they shouldn’t be mixed in your garden’s or tree’s soil in the winter. This is because it will likely stay there, unused during the colder weather. If the concentration is too high, it can kill off good microbes in the soil and possibly even burn the citrus tree’s roots (from the higher nitrogen). Again, this would only be in very high volumes.
However, if you’re just using a small handful of coffee grounds, you can simply scatter this over the surface of your citrus tree soil at any time of year. Just make sure the grounds aren’t directly touching the tree or its roots.
Lastly, keep in mind the soil’s pH. You don’t want to make the soil too acidic for your citrus trees or other plants. Since citrus trees prefer a soil pH of 6.0-7.0, it can become too acidic if you use too many coffee grounds.
When in doubt, to see if coffee grounds would make the soil too acidic, consider performing a pH test.
For more information on measuring your soil’s pH, you can check out my recommended tools page to see the pH meter I recommend.
And, if you want to see it in action, this video by Alberta Urban Garden will help demonstrate measuring your soil’s pH.
The best way to use coffee grounds for your citrus tree soil is to first add it to your compost pile and wait 2-3 months. Once it’s decomposed, you can apply the compost in 1-2 inch layers on top of the existing soil. However, like the coffee grounds, ensure the compost isn’t touching the tree.
Coffee grounds are one of the common food wastes we have in our home and adding it to our garden’s soil can provide quite a few nutrients. Just make sure you aren’t spiking your soil with a strong dose of caffeine.