I’ve been looking into different plant fertilizers and was wondering if common food scraps such as coffee grounds and eggshells would be any good for blackberry plants. The only problem was, there was not a lot of info out there. So, I did some more research.
Coffee grounds and eggshells are great for blackberry bushes as they add valuable nutrients such as nitrogen, phosphorus, potassium, and calcium. For example, coffee is 2% nitrogen and eggshells are 95% calcium. Both also regulate soil pH and feed beneficial soil life. Use no more than 2 cups of coffee grounds.
Let’s take a look at the benefits coffee grounds and eggshells provide and how we should use them on blackberry bushes.
Why Coffee Grounds Are Good for Blackberry Bushes
1. Nutrients
Here’s a list of nutrients found in coffee grounds:
- 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 in the soil.
This is good news as nitrogen is the primary nutrient plants require (along with phosphorus and potassium, together making “NPK”).
2. Acidic pH
Most plants, including blackberries, prefer a slightly acidic soil pH. For blackberry plants, the ideal range is between 5.5-6.5.
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
| Used Coffee Grounds | Fresh Coffee Grounds |
|---|---|
| pH of 6.8 | pH of 5.5-6.8 |
The best ways to measure your blackberry plant’s soil 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.
Fortunately, coffee grounds are fairly acidic, but they should be brewed or composted first to remove the excess caffeine.
3. Other Benefits
Coffee grounds also help blackberry bushes by increasing the soil’s water retention and temperature regulation (similar to compost). For example, every 1% increase in the soil’s organic matter leads to an additional 20,000 gallons of water held per acre.
Coffee grounds are also said to help repel some pests such as snails and slugs.
Thanks to how small coffee grounds are, they quickly decompose in the soil, becoming swift food for worms and other beneficial soil life. This decomposition process can be as quick as 1-2 weeks (especially in vermicompost bins) but can take as long as 3+ months.
How to Use Coffee Grounds on Blackberry Bushes
| 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.
Apply Directly to the Soil
If you have under 2 cups of coffee grounds, apply them directly to your blackberry bush’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 blackberry bush’s stems. Doing this improves aeration and sunlight exposure, reducing the chance of mold building up and affecting your plant.
Keep in mind, high levels of caffeine can be harmful to beneficial insects such as earthworms and pollinators. Since caffeine is a natural pesticide made by plants, avoid using too many coffee grounds in vermiculture bins or other beneficial insect areas.
During times when you have a lot of coffee grounds, it’s usually better to compost them first.
Compost
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 composting coffee grounds.
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
Since coffee grounds are a “green” material (nitrogen-based), they can make a compost pile stinky if used in excess. To balance this, add “brown” materials (carbon-based), such as leaves, sawdust, or wood chips.
Place the carbon materials on top of your compost pile to reduce and eliminate smells and flies. The finer the carbon material the fewer the bugs and stink.
Fortunately, coffee grounds don’t have as much nitrogen as other materials. Coffee grounds have a great carbon-nitrogen ratio (20-24:1), so they don’t need much carbon to become balanced.
For example, the famous permaculture farmer Joel Salatin recommends compost piles to have a carbon-nitrogen ratio of 30:1, so coffee grounds aren’t too far off on their own.
Why Eggshells Are Good for Blackberry Bushes
Nutrients
Following coffee grounds, many households have plenty of eggshells to spare and are looking for ways to repurpose them. Which is great news for their gardens. Here are the nutrients found in eggshells:
- Calcium
- Magnesium
- Potassium
- Iron
- Phosphorus
- Copper
- Zinc
- Manganese
- Sodium
Because eggshells are mostly made of calcium, they aren’t concentrated in other nutrients. However, they have decent amounts of phosphorus (0.3%), magnesium (0.3%), and a few other minerals.
Eggshells contain up to 95% Ca carbonate and various macro and micro-nutrients such as magnesium, potassium, iron, and phosphorus. Therefore, eggshells are also good for plant growth, stimulate root development, and can be reused to make fertilizers.
Agronomy & Crop Ecology, Journal of Plant Production Science, Taylor and Francis Online
Aside from root development, calcium benefits blackberry bushes by promoting strong cell walls and disease resistance.
Like coffee grounds, eggshells feed beneficial soil life which then support the plant’s life.
How to Use Eggshells on Blackberry Bushes
| 1 Cup or Less | Over 1 Cup |
|---|---|
| Apply directly to soil | Compost first |
Ideally, provide no more than 1 cup of eggshells every 3-6 months per plant. If you have a lot of eggshells, consider composting them first.
The easiest way to process eggshells for blackberry plants is to crush the eggshells and place them directly on top or underneath your plant’s soil. Adding them to your compost pile also works.
However, crushed eggshells take a while to decompose. For example, when I added crushed eggshells to our raised beds, I still found eggshell chunks 1 year later! Of course, the plant’s roots can’t use eggshells if they’re this large. But there’s a better method.
The best way to use eggshells on blackberry bushes is to turn the eggshells into a powder. This way the eggshells don’t need to be broken down into the soil nearly as much and are almost immediately available to be used by the plant’s roots.
Here’s how to do it:
- Preheat the oven to 200ºF
- Place eggshells on a baking sheet
- Bake for 30 minutes or until the eggshells are completely dry
- Grind the eggshells in a blender
This process also makes handling raw eggshells safer as any bacteria is being killed off. As with the above, avoid using more than 1 cup of eggshells every 3-6 months.
Eggshell powder easily blows away with the wind, so consider mixing it with compost or watering it down so it sticks to the soil and begins leaching into it.
Other Food Scraps for Blackberry Bushes
Other food scraps such as banana peels, veggies, and citrus peels are good natural fertilizers for blackberry bushes. They add nutrients such as potassium, calcium, magnesium, and manganese.
To see a full list of common food and yard scraps, and the nutrients they provide, check out my other post: Create an Amazing Homemade Fertilizer for Your Fruit Plants
You can also make your own vermicompost bin. To see how I made ours in less than 10-minutes and for under $50, check out our video below.
Sources
- https://ucanr.edu/sites/SoCo/files/27140.pdf
- https://doi.org/10.1080/1343943X.2022.2120506
- https://iopscience.iop.org/article/10.1088/1755-1315/755/1/012001/pdf
