Coffee grounds (and brewed coffee) are a source of nitrogen for plants, producing healthy green growth and strong stems. Coffee also contains calcium and magnesium — both of which are beneficial to plant health. To use coffee as a plant fertilizer, you'll need to dilute it. It should look like weak tea.
In most cases, the grounds are too acidic to be used directly on soil, even for acid-loving plants like blueberries, azaleas and hollies. Coffee grounds inhibit the growth of some plants, including geranium, asparagus fern, Chinese mustard and Italian ryegrass.
As an organic nutrient, coffee grounds are suitable for most plants. However, since coffee slightly acidifies the soil, it is beneficial for roses, hibiscuses, begonias, and other plants prefer substrates with an acidic or slightly acidic reaction.
Coffee grounds are highly acidic, they note, so they should be reserved for acid-loving plants like azaleas and blueberries. And if your soil is already high in nitrogen, the extra boost from coffee grounds could stunt the growth of fruits and flowers.
It's okay to water plants with leftover coffee or to add coffee grounds to the compost pile but learning when and why to use coffee in the garden will protect your plants. Only use black, unflavored coffee with this method to offer plants a source of nitrogen which can fertilize certain indoor and outdoor plants.
"It's fine to use coffee as a fertilizer," our senior lab testing technician, Jonathan Chan, says. "However, you should be careful because coffee can raise the acidity of the soil. Caffeine also is known to have a negative effect on plant growth."
Apparently, coffee is a great source of nitrogen, and plants that enjoy more acidic soil can benefit from certain levels of nitrogen, like blueberries, azaleas, and rhododendrons. According to The Spruce, if you plan on doing this, you'll need to keep a close eye on your plant.
Don't just pour it down the drain — you can use it to fertilize your plants, both indoor and outdoor. Coffee grounds (and brewed coffee) are a source of nitrogen for plants, producing healthy green growth and strong stems. Coffee also contains calcium and magnesium — both of which are beneficial to plant health.
Can you add coffee grounds to potted plants? Yes, it's possible, but it should not be more than a thin sprinkling. If you add too much, the coffee grounds will form a dense layer on the surface of the potting soil that is impenetrable to water.
Coffee grounds contain around 2% nitrogen as well as varying amounts of phosphorus and potassium which are all very important for the growth of tomato plants.
The shells also contain other minerals that help plants grow, including potassium, phosphorus, and magnesium. Eggshells are, therefore, an effective and inexpensive fertilizer for outdoor garden soil and houseplants.
Like sulphur, cinnamon is a natural fungicide that helps most plants root, while inhibiting the spores that cause rot in stem cuttings. Dip prepared plant stems in cinnamon and push them into the soil. It's an effective rooting hormone that's easy to use and inexpensive.
Since coffee grounds have such a pungent and intense smell, mosquitoes do not like to come near it. Mosquitoes are repulsed by all types of coffee, whether it is fresh, used, or burnt. The most effective way to use coffee grounds for mosquito control is by burning them, as it creates a stronger aroma.
Coffee Grounds to Deter Pests
Coffee grounds are commonly used to keep animals including slugs, snails, rabbits and fire ants from eating plants in the garden, and to keep cats from treating garden beds like litter boxes.
There are a select few plants that can benefit from fresh grounds—including acidity-loving Hydrangeas, Rhododendrons, Azaleas, Lily of the Valley, blueberries, carrots, and radishes—but generally, most common houseplants will prefer low to no acidity.
Coffee grounds can be used when planting perennials, shrubs and bushes, or added to the soil around those growing throughout the year. Adding a few tablespoons when planting perennials helps add nutrients and soil structure for long-term growth.
If you don't use enough coffee, it will result in a weak, thin, flat, and watery cup. On the other hand, if you use too much of the good stuff, this will make the coffee feel muddy, heavy, and off-balance, without any real depth. You can experiment with the amounts but don't depart too far from the recommended ratio.
Which plants shouldn't you try this with? Don't add eggshell fertilizer to plants that prefer acidic soil, like blueberries. Ericaceous plants such as mountain laurel, pieris and azaleas also fall into that category. In extreme cases, low acidity for plants could impact their overall health and/or the resulting crop.
You may love your morning coffee, but ants could do without it. Another natural way to deter ants, sprinkle coffee grounds outside and around your garden. The smell repels them and they'll be looking for a less caffeinated place to hang out. Want to keep your home clean and clear of ants?
Dried coffee grounds can be stored in plastic, a glass jar, or even paper packaging. These are the containers after a week. There is no evidence of mould or of the grounds getting lumpy, and they smell like fresh coffee. I'm using newspaper at the tops of the jars to absorb any remaining moisture.
Coffee grounds are rich in nutrients, especially nitrogen. They also have some amount of other nutrients like potassium and phosphorous. Overall, this means that adding coffee grounds to your garden can work fairly well as a fertiliser. Coffee should be spread in a thin layer, rather than being clumped in one place.
While plants need nitrogen (remember the NPK on fertilizers), too much nitrogen will create lots of green leaves but few berries or fruits. This means potassium-rich banana peels are excellent for plants like tomatoes, peppers or flowers. Banana peels also contain calcium, which prevents blossom end rot in tomatoes.
Flowering Houseplants
Optimal pH: 6.0-6.5. Coffee grounds can improve soil acidity and provide essential nutrients for healthy growth and flowering.