I recently bought a small raspberry plant and I wanted to see if I could add our leftover coffee grounds to its soil. The only problem was, there was not a lot of info out there. So, I did some more research. Here’s what I found.
Coffee grounds are great for raspberry plants as they have essential nutrients such as nitrogen, potassium, and phosphorus. They also promote beneficial soil life such as mycorrhizal fungi. Remember to apply a maximum of 2 cups per plant and mix with other organic matter to avoid soil compaction and mold.
So, while coffee grounds are good for raspberry plants, which nutrients do they provide, and is their acidity (and caffeine) an issue? Let’s find out.
3 Benefits of Coffee Grounds For Raspberry Plants
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
As with most plants, raspberries prefer a slightly acidic soil pH (5.6-6.2). This is because a slight acidity dissolves the nutrient solids in the soil and makes them accessible to the plant’s finer roots.
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 raspberry 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. Water Retention, Temperature Regulation, and Pest Repellant
Coffee grounds also help raspberry plants 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 Raspberry Plants
| 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 (if you haven’t already) 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 raspberry plant’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 raspberry plant’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.
10 Other Kitchen and Yard Scraps for Raspberry Plants
1. Banana Peels
Banana peels contain lots of potassium, phosphorus, and magnesium, all essential nutrients for healthy plant growth and development. Just chop them up and bury them around your raspberry plants, and watch them thrive.
2. Citrus Peels
Orange, lemon, and other citrus peels are rich in nitrogen and potassium and can help lower the pH of the soil, making it more acidic. This is perfect for your raspberry plants, which prefer slightly acidic conditions.
3. Carrot Tops and Peels
Carrot scraps, including tops and peels, are a great source of potassium and can help improve soil structure. Just add them to your compost pile or directly bury them in your raspberry bed for a nutrient boost.
4. Tomato Trimmings
Tomato scraps, like stems and leaves, are abundant in nitrogen and potassium. They decompose quickly, providing valuable nutrients to your raspberry plants. Plus, they’re a great way to reduce waste in your kitchen.
5. Lettuce and Spinach Leaves
These leafy greens are rich in nitrogen, which is essential for healthy plant growth and development. Add them to your compost pile or use them as mulch around your raspberries.
6. Potato Peels
Potato peels are another excellent source of potassium and phosphorus, both of which promote root development and overall plant health. Toss them into your compost or bury them near your raspberry plants for a nutrient boost.
7. Squash and Pumpkin Scraps
Squash and pumpkin peels are high in nitrogen, phosphorus, and potassium, all of which benefit your raspberry plants. Add them to your compost or use them as mulch for a well-rounded nutrient mix.
8. Eggshells
Crushed eggshells are an excellent source of calcium (about 95% calcium), which is essential for raspberry plants to develop strong cell walls and healthy root systems. Be sure to rinse and crush the eggshells before adding them to your compost pile or sprinkling them around your plants.
Tip: Bake used eggshells for 30 minutes at 400ºF to sterilize and dry them before putting them in a blender. Eggshell powder is much easier to decompose in the soil. You can also feed them back to chickens to give them a calcium boost.
9. Leaves and grass clippings
Green leaves and grass clippings provide nitrogen, which serves as a food source for soil microorganisms and promotes plant growth. Layering these materials with other compost ingredients can help maintain a proper balance of carbon and nitrogen in your compost pile.
10. Straw and Hay
Straw and hay make excellent carbon-rich additions to your compost pile. They help to create air pockets and improve drainage in the compost, both essential for healthy decomposition. Plus, they’re a great way to repurpose agricultural waste!
