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.
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.
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.
'Your roses, azaleas, lilies, and hollies because they are acid-loving plants that will thrive best in the acidic characteristic of coffee grounds,' he adds.
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 are effective at repelling pests because of the strong smell. The smell of coffee is repulsive to many bugs and will keep them away from treated areas. Coffee grounds can be used fresh or used, but unused coffee grounds are more effective at repelling pests.
Coffee's bitter compounds are responsible for its repelling effects. These compounds make the coffee unpalatable to rats and mice. They will avoid areas where there is the use of coffee grounds.
You may wonder if any animals are attracted to coffee grounds. Mice and rats pay little attention to the smell of coffee and rarely eat coffee grounds. However, there are smells these, and other pests hate. So, if you want to keep pests away, then here are some smells most of them hate.
Other Natural Repellents
Mothballs — place them around the perimeter, and their pungent smell will repel snakes. Vinegar — mix it with water and spray often. Caffeine — sprinkle coffee grounds or instant coffee granules. Spices — chili powder and cayenne pepper work the best.
Coffee grounds don't work on potted plants, but if you have some succulents planted outside in your garden, you can place used coffee grounds directly onto the soil. As the used coffee grounds break down, they'll add nitrogen to the soil, a vital succulent nutrient.
Coffee grounds inhibit the growth of some plants, including geranium, asparagus fern, Chinese mustard and Italian ryegrass. Conversely, grounds (used as mulch and compost) improve yields of soybeans and cabbage.
Roses do like coffee grounds, but too much too close can give them a nasty nitrogen burn and can kill your roses. Never sprinkle coffee grounds right next to the plant.
Coffee grounds are an excellent fertilizer, especially for orchids and African violets.
Additionally, the sharp edges of coffee grounds can deter snails from crawling over them. Studies have shown that coffee grounds are an effective way to deter snails (and other pests). In one study, coffee grounds were found to reduce the number of snails by up to 50%.
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.
Why coffee grounds? Since the bears have a strong sense of smell, such a pungent treat is extremely attractive and stimulating to them. The bears roll around in coffee grounds like a cat in catnip!
Asian Palm Civet
These are likely the most well-known animals that process coffee by eating the cherries and pooping out the beans. Known better as the kopi luwak, this coffee was once (and still may be) some of the most expensive coffee beans available.
This makes peppermint oil, chili powder, citronella, and eucalyptus the most common natural rodent repellents. Chemical smells, such as ammonia, bleach, and mothballs also work as mice deterrents.
But what exactly do mice and rats hate to smell? Mice can be kept away by using the smells of peppermint oil, cinnamon, vinegar, citronella, ammonia, bleach, and mothballs.
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's really everything they need in order to establish a colony," Counsell explained. Counsell says cleanliness is. Ants can be attracted to even a trace of leftovers like coffee residue.
Coffee Grounds: False
However, in a 2020 study published in the International Journal of Science and Healthcare Research, researchers tested this out and found that coffee grounds were not very effective at repelling cockroaches.
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.