I’ve been wanting to grow blueberry bushes soon and I’ve heard they like acidic soil, so I was wondering if coffee grounds would make a good fertilizer for them. Here’s what I found.
Coffee grounds are good for blueberry plants as they add nitrogen, phosphorus, potassium, and acidity. While coffee grounds have a pH of 5.5-6.8, blueberries prefer more acidity, around 5.0 so it is recommended to add more acidic amendments such as peat moss. Apply no more than 2 cups of coffee grounds per plant.
So while coffee grounds seem like a good fertilizer for blueberry bushes, what exactly do they do to the soil, and what’s the best way we can fertilize blueberry plants with them? Let’s take a closer look.
Benefits of Coffee Grounds For Blueberry Plants
Nutrients
- Nitrogen
- Phosphorus
- Potassium
- Calcium
- Magnesium
- Boron
- Copper
- Iron
- Zinc
Coffee grounds also increase the acidity of the soil, which is helpful for blueberries as they prefer acidic soil with a pH of 4.5-5.5 (source).
The three main nutrients blueberry plants (and most other plants) need are nitrogen, phosphorus, and potassium, abbreviated as “NPK”. Fortunately, coffee grounds provide all three of these nutrients, along with other secondary nutrients such as calcium, magnesium, copper, iron, boron, and zinc.
Coffee grounds are also slightly acidic with a pH of 5.5-6.8, which is pretty much perfect for blueberry plants since they prefer acidic soil.
However, used coffee grounds generally have less acidity than fresh grounds due to the process of brewing (drawing out the acidity).
| Used Coffee Grounds | Fresh Coffee Grounds |
|---|---|
| pH of 6.8 | pH of 5.5-6.8 |
Fresh coffee grounds are better for blueberry plants than used grounds.
Used coffee grounds generally have a pH closer to 6.8, which is still good for blueberry plants. Although, you may need to supplement the soil with additional acidic amendments.
Acidic amendments include peat moss or anything lying around the house that contains sulfur, such as leaves, onion skin, broccoli stems, asparagus stalks, or beans along with the used coffee grounds if your soil is too alkaline.
So, why is soil pH so important for blueberry plants?
If a soil’s pH is either too acidic or alkaline for the plant, it will be unable to absorb nutrients. Over time, this binding of nutrients can lead to leaves and fruit wilting, yellowing, browning, and dropping.
To help with this, when you add any amendments to the soil (including coffee grounds), it’s a best practice to periodically check the soil’s pH.
The best ways to measure the soil’s pH are either with pH strips or a pH meter. I prefer using a meter since they’re affordable and easy to use. If you’d like to see which pH meter I use and recommend, visit my recommended tools page.
If you do find that your blueberry plant’s soil pH is too acidic (below 4.5), consider adding alkaline materials to the soil like biochar, powdered lime, or wood ash.
On the other hand, if your blueberry plant’s soil pH is too alkaline (above 5.5), use acidic amendments such as sand, onion skin, or peat moss.
How To Use Coffee Grounds as a Blueberry Plant Fertilizer
If you have a handful of coffee grounds, you can apply it directly onto your plant’s soil.
If you have more than 1 cup of grounds, consider composting it first to decrease the caffeine. Usually, it takes about 2-3 months for the coffee grounds to decompose and become usable by the plant.
Depending on how many coffee grounds you have, and what you prefer, there are a few ways you can use coffee grounds as a blueberry bush fertilizer:
Directly to the Soil
If you have under 2 cups of coffee grounds, apply them directly to your 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 blueberry bushes terminal stem. Doing this improves aeration and sunlight exposure, reducing the chance of mold building up.
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 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.
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.
You can also mix the coffee grounds with mulch. Some good mulches to use for blueberry plants are straw, bark, leaves, and pine needles.
Looking for some homemade, natural alternatives to chemical fertilizer? Check out my article: Create an Amazing Homemade Fertilizer for Your Fruit Trees.
How Many Coffee Grounds Should You Use on Blueberry Plants?
Add no more than 2 cups of coffee grounds to your blueberry plant at a time.
As a general rule, keep the used coffee grounds below 15% of your total soil or compost content. For the occasional espresso brick, you can apply it directly. For the daily pot, consider composting it first.
Using an excess with your blueberry plant or compost pile can create imbalances in nutrients and soil life.
If you’re not sure how many coffee grounds to apply, it’s always a good idea to start with small amounts and work your way up gradually (or you can keep it easy and compost them first).
If you’re composting the coffee grounds first, allow 2-3 months for them to fully decompose. After, apply the compost in 1-2 inch layers around the blueberry plant.
For best results, 2 weeks after you apply coffee grounds, measure your blueberry plant’s soil pH and check for any growth issues. This isn’t necessary, but it’s recommended if you’re applying large amounts of coffee grounds.
Some signs that you might be applying too many coffee grounds are if your blueberry bush’s leaves are turning yellow and dropping. This is likely a result of excess nutrients or moisture building up.
However, this is highly unlikely unless you’re using WAY more than the above suggested amounts (generally, above 15-20% of the soil’s total volume).
If you do find that you have extra coffee grounds, and are looking to use them on your other plants, consider giving them to the blueberry’s companion plants.
When Should You Apply Coffee Grounds to Your Blueberry Plants?
The best time to apply coffee grounds to blueberry plants is in the early spring and throughout the rest of the growing season. Avoid using coffee grounds on blueberry plants in the winter as the plants typically go dormant and don’t require many nutrients.
If applied in the winter, the coffee ground’s nutrients will go largely unused and simply sit in the soil for several months. With enough time, the extra nutrients and moisture can build up, leading to complications. Instead, add coffee grounds to your compost bin (or pile) in the winter.
Will Coffee Grounds Hurt Blueberry Plants?
Some say that coffee grounds contain too much acidity and caffeine to be used on the soil. But does this hold any truth?
Caffeine is a natural defense mechanism made by plants to repel insects. This makes it a naturally occurring pesticide. Generally, pesticides can cause more harm than good since they also kill pollinating insects and beneficial life in the soil. However, the science is mixed on the amount of caffeine left in coffee grounds.
However, some sources mention used coffee grounds can still be harmful to plant and soil life.
So, to stay on the safe side, the best solution here would be to compost your coffee grounds and let the caffeine and acidity break down. After some time in the compost pile, the nutrients should be the only things remaining from the coffee grounds.
Still, if you’re applying a small volume of coffee grounds infrequently, it’s likely not going to harm the soil.
Use fresh coffee grounds rather than used coffee grounds when it comes to blueberry plants. The soil prefers fresh grounds’ pH level.
Final Thoughts
Coffee grounds are great for blueberry bushes because they add plenty of nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium, and copper. It also provides acidity to the soil and promotes beneficial soil life.
Just as important, coffee grounds also greatly improve the soil’s richness and water retention. In fact, each 1% increase in the richness of the soil can help it hold 20,000 gallons more per acre (source).
Keep in mind to check your blueberry plant’s soil pH every now and then. If you’d like a visual on how to do so, check out this helpful video below by Alberta Urban Garden!
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