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.
Excessive acidic soil can kill or hamper the growth of plants like asparagus fern, Chinese mustard, Italian ryegrass, lavender, orchids, rosemary, tomatoes, and geranium. The roots of these plants are also not potent to absorb the nutrients added by the coffee grounds in the soil.
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.
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.
How Often Should You Add Coffee Grounds to Plants? You can fertilize houseplants an average of 7 to 10 days in a row, but no more, as there is a risk of over-acidification of the soil. A cup of ground coffee should be added to the compost once a week.
'Coffee grounds are an excellent houseplant fertilizer due to their high nitrogen content (about 2 per cent) that releases slowly into the potting media as they decompose. However, coffee grounds have more to offer to plants than just nitrogen,' she says.
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 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.
One study published in the Journal of Agricultural and Food Chemistry found that coffee grounds were more effective at repelling rodents than commercially available products. Coffee's bitter compounds are responsible for its repelling effects. These compounds make the coffee unpalatable to rats and mice.
Eggplant, peppers, broccoli, cauliflower and leafy greens, to name a few. But don't go overboard. Since it takes a while for the shells to decompose, Uyterhoeven recommends applying eggshell fertilizer to your garden or indoor plants just twice a year—in the fall and spring.
One final note: Make sure your soils aren't already alkaline before you add anything to up the pH; and never ever use eggshells or other pH-raisers around acid-loving plants like azaleas and rhododendrons.
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 any type of fertilizer, coffee grounds are only effective when used sparingly. It is never a good idea to add too much, as that could do more harm than good. The proper proportion is usually around 4 to 1, or twenty-five percent of coffee grounds to mineral soils by volume.
These things are great for nutrient poor lawns and lawns on clay or sandy soil. However, coffee grounds still contain some residual caffeine, which can cause harm to the micro fauna in your soil, and that's why it is not recommended to apply coffee waste directly to your lawn.
Not only do they repel mosquitoes, but also other insects such as wasps and bees. Coffee grounds are the bee's knees when it comes to staying bug bite free. Most bugs have a very strong sense of smell. Coffee grounds are very potent and even more potent once they are burned.
“the smell of the coffee repels snails, slugs and ants. You may also have success using coffee grounds to repel mammals, including cats, rabbits and deer.”
Coffee beans, grounds and brewed coffee contain caffeine, a very dangerous and toxic chemical to cats and dogs. Ingestion can be life threatening. According to the Pet Poison Helpline, a moderate amount of coffee can easily cause death in small dogs or cats.
Acid Fertilizer
Those acids can be beneficial for plants, too. Acid-loving plants need a fertilizer with a low pH level. And Coke works. Try pouring a little bit of Coke in the garden around the base of your plants in the soil (not on the plant or roots itself).
These mainstays love the acid and nutrients that coffee grounds add to the soil. Coffee grounds also help soil hold on to water for happy plants. Be sure to spread the coffee grounds out and rake them into the soil. Otherwise, they can form a crust that prevents water from penetrating to the roots.
Some gardeners report success in turning their hydrangeas blue by applying coffee grounds to the soil. The coffee grounds make the soil more acidic, allowing the hydrangea to more easily absorb aluminum. In addition, fruit peels, lawn clippings, peat moss and pine needles, are thought to have a similar effect.