It’s time to give our lemon tree some fertilizer, and we were wondering if we could use the leftover coffee grounds from our morning coffee maker. So, I did some more research. Here’s what I found.
Coffee grounds are great for lemon trees as they provide nutrients (such as nitrogen), acidity, and organic matter. Since lemon trees require double the nitrogen compared to other fruit trees, coffee grounds are especially beneficial. However, avoid using too many coffee grounds. For best results, stay under 2 cups.
So, while coffee grounds are great for lemon trees, what are more of their benefits, how should we use them, and how often? Let’s take a closer look.
In this article:
- 3 Reasons Coffee Grounds Are Good For Lemon Trees
- How to Use Coffee Grounds
- Potted Lemon Trees & Coffee Grounds
- My Recommended Fertilizer for Lemon Trees
- Are Eggshells Good to Use?
3 Reasons Coffee Grounds Are Good for Lemon Trees
There are three main reasons coffee grounds are good for lemon trees:
- Contains essential nutrients
- Has an acidic pH, which most plants prefer
- Increases the organic matter in the soil (healthier soil and better water retention)
(Bonus) The strong scent helps repel pests such as deer, slugs, snails, and more.
1. Nutrients
For starters, coffee grounds contain plenty of nutrients for plants such as:
- Nitrogen
- Phosphorus
- Potassium
- Calcium
- Magnesium
- Boron
- Copper
- Iron
- Zinc
The most potent nutrient in coffee grounds is nitrogen, which is around 2%. While this might not seem like a lot, it quickly adds up in the soil.
Nitrogen is also the primary nutrient that plants require (along with phosphorus and potassium, together making “NPK”).
On top of that, compared to other fruit trees, citrus and avocado trees require double the nitrogen as they are heavy feeders. These plants use nitrogen to grow their thick canopy and establish a strong root system.
For these reasons, coffee grounds are one of the best kitchen scraps to use on lemon trees.
Tip: If you’d like free coffee grounds, ask your local coffee shop for their used coffee grounds. They normally have 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.
2. Acidic pH
Coffee grounds are also great for lemon trees as they promote a slightly acidic soil pH. Like most plants, lemon trees prefer a slightly acidic soil pH of 6.0 to 7.0.
The problem is, without a proper pH, lemon trees are unable to absorb nutrients in the soil. 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
On the other hand, coffee grounds have an acidity between 5.5 and 6.8, depending on if (and how long) they were brewed.
| Used Coffee Grounds | Fresh Coffee Grounds |
|---|---|
| pH of 6.8 | pH of 5.5-6.8 |
Because of this, coffee grounds should still be brewed or composted to remove excess caffeine and acidity before being applied to lemon trees.
You can also check your lemon tree’s soil pH before and after you apply coffee grounds.
For example, the best way to measure your soil’s pH are with pH 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 lemon 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.
3. Improved Soil
Coffee grounds also help lemon trees by improving the soil’s organic matter (similar to compost), which increases the soil’s water retention and temperature regulation.
And with every 1% increase in the soil’s organic matter, an additional 20,000 gallons of water is held in the soil, per acre.
Tip: Like compost, coffee grounds can be used to fix soil drainage (both fast and slow). The added organic matter breaks up the larger clumps of soil as well as promotes the proper amount of water retention. This means coffee grounds are a great amendment for clay soils.
Also, after the caffeine has left the coffee grounds, the nutrients are great at feeding the beneficial soil life such as earthworms and mycorrhizal fungi.
Mycorrhizal fungi promote many aspects of plant life, in particular improved nutrition, better growth, stress tolerance, and disease resistance.
Department of Biology, University of Fribourg, Switzerland
So, coffee grounds are a great way to give your lemon tree essential nutrients, a balanced soil pH, and a higher quality of soil!
But, just how much should we use?
How to Use Coffee Grounds on Lemon Trees (2 Ways)
I recommend applying 2 cups of used (brewed) coffee grounds around your lemon tree every 1-2 months. If you have more than this, it’s best to compost it as the nutrients and acidity can become too potent for the lemon tree.
Here’s a quick summary I put together:
| Under 2 Cups | Over 2 Cups |
|---|---|
| Apply directly to the soil every 1-2 months | Add to a compost pile (no more than 20-35%) |
| Spread in a 1/2-inch layer to avoid mold | Wait 3 months for decomposition |
| (Optional) Mix with soil to dilute | Apply 2 inches of compost every 1-2 months |
If you’d like to learn more about using coffee grounds for lemon trees, here are some more details.
1. Apply Directly to Soil (Under 2 Cups)
If you’re not frequently applying coffee grounds and have under 2 cups, I recommend applying it directly to your lemon tree’s soil by spreading it out in a thin, 1/2-inch layer underneath the tree’s canopy.
Spreading the coffee grounds out improves aeration and sunlight exposure, reducing the chance of mold growing.
As far as where to apply the coffee grounds (or any other amendment), put them under the lemon tree’s canopy (drip line) as this is the root zone. Any further and the nutrients are beyond the reach of the roots.
Also, keep coffee grounds at least 3 inches from the tree’s trunk to prevent mold buildup.
Keep in mind, high levels of caffeine can be harmful to beneficial insects such as earthworms and pollinators. This is because caffeine is a natural chemical made by plants to repel insects. Avoid using too many coffee grounds in vermiculture (worm) bins or other beneficial insect areas.
However, coffee grounds are good at repelling some pests such as deer, snails, slugs, and even rodents.
Overall, if you make a daily pot of coffee, you likely have too many coffee grounds for just one lemon tree. In this case, it’s best to spread them out to the rest of your garden or put them in a compost pile.
2. Compost Coffee Grounds (Over 2 Cups)
If you make coffee daily or have over 2 cups of coffee grounds, it’s best to add them to your compost pile. After 3 months, the coffee grounds should be free of caffeine and decomposed enough to be used for your lemon trees and the rest of your garden.
Because coffee grounds have a great carbon-nitrogen ratio (20-24:1), they’re amazing to use in compost.
For example, renowned farmer Joel Salatin says compost piles should have a carbon-nitrogen ratio of 30:1.
So, we just need to supplement the coffee grounds with a bit more carbon to reach that 30:1 ratio.
Maintaining sufficient carbon (“brown” materials) such as sawdust, dead leaves, and wood chips in compost piles helps them decompose properly. It also helps them not get stinky from the nitrogen-rich (“green” materials) such as green leaves, grass clippings, and food scraps.
So, when adding coffee grounds to your compost pile or bin, it’s best to add a handful or two of leaves, sawdust, wood chips, or other carbon materials.
Tip: Placing a 1-2 inch lay of fine carbon material such as sawdust on top of compost piles helps to suppress and eliminate smells and flies.
Can You Add Too Much Coffee Grounds in Compost?
Here’s what a gardening expert has to say:
Use no more than 20-35 percent by volume of coffee grounds in a compost pile.
Lisa Ogden, University of Wyoming
The average compost pile is 3x3x3 feet and weighs around 1,250 pounds. So, for 20-35% of the total volume of compost, you’d need between 250 and 438 pounds of coffee grounds (within a 3 month period) for it to be too much.
As you can see, it’s difficult to go overboard when adding coffee grounds to a compost pile. You’d have to drink a lot of coffee for that to be the case.
Potted Lemon Trees & Coffee Grounds
Potted lemon trees benefit from coffee grounds in the same way as planted lemon trees, but since they have a limited amount of soil, they require much less.
For a 5-gallon lemon tree, I recommend either applying a 1/2-inch layer of coffee grounds on top of the soil or mixing 2 cups into the potting mix.
Keep in mind, if you leave a clump of coffee grounds on top of the soil there’s a good chance it can grow mold (especially since there’s limited sunlight and airflow indoors). Because of this, consider covering the coffee grounds with a layer of potting soil.
My Recommended Fertilizer for Lemon Trees
The best fertilizer to use for lemon trees is one that has an NPK (nitrogen, phosphorus, and potassium) ratio of 2:1:1. For example, a 6-3-3 fertilizer works well.
When looking for fertilizer, aim for one that is organic and slow-release. Chemical and fast-release fertilizers may have nutrients in quantity, but they often lack quality and can dry/kill healthy soil (turning it into dirt).
To see which lemon tree fertilizer I use and recommend, see my recommended fertilizer page.
When To Fertilize Lemon Trees
According to Down to Earth and The University of Arizona Cooperative Extension, lemon trees should be fertilized 3 times per year:
- Jan/Feb
- Apr/May
- Sep/Oct
Because lemon trees are evergreen (keeping their leaves year-round) and commonly fruit 1-2 times per year, they typically require more frequent feeding than cold-climate plants.
How Much Fertilizer to Use On Lemon Trees
The amount of fertilizer you use depends on the size of your lemon tree. Generally, it’s recommended to apply 1 cup of fertilizer per 1 inch of trunk diameter.
Are Eggshells Good For Lemon Trees?
Eggshells are a great supplement for lemon trees as they’re 95% calcium and help feed the soil. To promote the best nutrient uptake, bake the eggshells on a pan at 400ºF for 30 minutes. Then, put them into a blender and blend until they’re powdered. Apply evenly on the soil and mix in so it doesn’t blow away.
The increase in surface area means the soil life and the lemon tree’s roots can absorb it much easier.
For more about composting coffee grounds (and eggshells), check out easy composting by Growit Buildit.
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.arizona.edu/node/5315
- https://helpmecompost.com/compost/basics/how-much-does-compost-weigh/
