We drink a lot of coffee at home and have several citrus trees such as lemon, orange, lime, and tangerine. Instead of throwing the coffee grounds away, we were wondering if they’d be any good for the garden. I did some research to find out more.
Coffee grounds contain a good amount of nitrogen, phosphorus, magnesium, and copper, all of which help maintain healthy citrus trees. They also increase the soil’s acidity, which is helpful as citrus trees prefer slightly acidic soil with a pH of 6.0-7.0. Apply no more than 2 cups of coffee grounds per tree.
So, while coffee grounds are good for citrus trees, are there any other benefits, and how should we be applying them? Let’s take a closer look.
Benefits of Coffee Grounds For Citrus Trees
Nutrients
- Nitrogen
- Phosphorus
- Potassium
- Calcium
- Magnesium
- Boron
- Copper
- Iron
- Zinc
By far the most potent nutrient in coffee grounds is nitrogen (at about 2%). This might not seem like a lot, but it adds up quickly when applied to the soil.
This is good news as nitrogen is the primary nutrient plants need (along with phosphorus and potassium, together making “NPK”). Additionally, citrus trees are heavy feeders and require double the nitrogen compared to other fruit trees.
As a result, coffee grounds make an amazing soil amendment and boost in nutrients for citrus trees.
Pro-Tip: If you’d like free soil amendment, ask your local coffee shop for used coffee grounds. The coffee shop near me has dozens of bags that they normally toss, and most shops love when people repurpose them. Keep in mind these coffee grounds are probably not organic.
Acidic pH
Like most plants, citrus trees prefer a slightly acidic soil pH of 6.0 to 7.0.
This is because a slightly acidic soil helps dissolve the nutrient solids in the soil, making them accessible to the plant’s finer roots.
Fourteen of the seventeen essential plant nutrients are obtained from the soil. Before a nutrient can be used by plants it must be dissolved in the soil solution. Most minerals and nutrients are more soluble or available in acid soils than in neutral or slightly alkaline soils.
Donald Bickelhaupt, SUNY College of Environmental Science and Forestry
Fortunately, coffee grounds are fairly acidic, but they should be brewed or composted first to remove the excess caffeine and acidity.
| Used Coffee Grounds | Fresh Coffee Grounds |
|---|---|
| pH of 6.8 | pH of 5.5-6.8 |
The best ways to measure your soil’s pH are with strips or a meter. I prefer using a pH meter since they’re affordable and easy to use. If you’d like to see which meter I use and recommend, see my recommended tools page.
If you find that your citrus tree’s soil pH is too acidic (below 6.0), consider adding alkaline materials to the soil like biochar, powdered lime, or wood ash.
On the other hand, if your soil pH is too alkaline (above 7.0), use acidic amendments such as peat moss, sand, and of course—coffee grounds.
Coffee grounds also help citrus trees by increasing the soil’s water retention and temperature regulation (similar to compost).
How to Use Coffee Grounds On Citrus Trees
| Under 2 Cups | Over 2 Cups |
|---|---|
| Apply directly to the soil | Add to compost pile (no more than 20-35%) |
| Spread out in a thin layer to avoid mold | Wait 3 months for decomposition |
Before using coffee grounds in your garden, I recommended brewing them first to remove most of the caffeine and excess acidity.
Directly to the Soil
If you have under 2 cups of coffee grounds, apply them directly to your citrus tree’s soil by spreading them out in a thin layer.
It’s recommended to have a layer no higher than 1/2 an inch and to keep the coffee grounds at least 3 inches from your citrus tree’s trunk. Doing this improves aeration and sunlight exposure, reducing the chance of mold building up and affecting your citrus tree.
High levels of caffeine can be harmful to beneficial insects such as earthworms and pollinators. Since caffeine is a natural chemical made by plants to repel insects, avoid using too many coffee grounds in vermiculture bins or other beneficial insect areas.
In these cases, it’s safer to compost the coffee grounds first.
In a Compost Pile
If you have over 2 cups of coffee grounds, add them to your compost pile. After 3 months, the coffee grounds should be free of caffeine and decomposed enough to be used in your garden.
Here’s what a gardening expert has to say about using coffee grounds in compost.
Composting coffee grounds is the best thing to do before putting them in the garden. Use no more than 20-35 percent by volume of coffee grounds in a compost pile.
Lisa Ogden, University of Wyoming
Because coffee grounds have a great carbon-nitrogen ratio (20-24:1), they’re amazing to use in compost.
Farmer Joel Salatin recommends compost piles have a carbon-nitrogen ratio of 30:1, so coffee grounds aren’t too far off.
Maintaining sufficient carbon (“brown” materials) in compost piles helps them decompose properly and not get stinky from the nitrogen-rich (“green” materials) such as green leaves, grass clippings, and food scraps.
To help balance the nitrogen coffee grounds in your compost pile, add a handful of carbon materials such as leaves, sawdust, or wood chips.
Place carbon materials on top of compost piles to reduce and eliminate smells and flies.
Other Kitchen and Yard Scraps for Citrus Trees
Some other kitchen and yard scraps that are great for citrus trees include:
- Eggshells
- Banana Peels
- Citrus Peels
- Potato Peels
- Grass Clippings
- Fallen Leaves
For example, eggshells contain about 95% calcium, while banana and citrus peels contain lots of potassium.
While citrus trees need nitrogen the most, other nutrients such as phosphorus and potassium are helpful in flowering and fruiting.
If you’d like to see which primary nutrients the above list provides citrus trees (along with a long list of other food and yard scraps), check out my post on homemade citrus tree fertilizer.
Sources
- https://www.uwyo.edu/barnbackyard/_files/documents/magazine/2017/summer/plantsperk0717.pdf
- https://www.discovery.com/science/Coffee-Grounds-in-Your-Garden
- https://extension.oregonstate.edu/gardening/techniques/coffee-grounds-composting
