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.
Compost coffee grounds for a vegetable garden instead of using them directly. Remember, coffee grounds are not good for tomatoes or seedlings. Get a soil test, especially if your plants are not thriving or you want to change the acidity of the soil.
The myth: coffee grounds are good for acid-loving plants
So it follows that they wouldn't mind the acidic nature of coffee (assuming that it is, of course). But not all plants like higher acid levels, and it's hard to compost/fertilise in a vacuum - risking damaging some of the others.
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. The smell of burnt coffee is also effective at repelling pests.
You can control them with coffee grounds, a safe and effective way to keep pests away. 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.
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.
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.
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.
You know that last bit of coffee that always seems to be left in the carafe? 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.
The green fungus called Trichoderma, is very beneficial to the soil. The blue-green fungus is moderately beneficial. At any rate, moldy coffee is good to use directly in the garden, on your houseplants, or in the compost pile.
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.
Sarah says the key is composting them first. "Give it six months to a year. The compost will break down the phytotoxins, and you'll still get the great benefit to the soil from using them."
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.
She recommends that grounds make up no more than 15 to 20% of the total compost volume. Because they are acidic, coffee grounds make good acid mulch. Of course, too much of anything is just too much, so apply coffee grounds in limited amounts.
Composting used coffee
Ensuring a balanced mix of 'wet' and 'dry' materials is the best way to achieve good compost. The nutrients contained in coffee grounds will be recycled back onto the soil when finished compost is used as a mulch or dug into the soil. Also add any un-drunk coffee to dry material in a compost bin.
Tomato Plants Like Slightly Acid Soil
The main reason that this idea that coffee grounds can help to fertilize your tomato plants is that tomato plants thrive in slightly acidic soil. Used coffee grounds can help soil become slightly more acidic when they are used as fertilizer.
Broccoli, cauliflower, Swiss chard, spinach and amaranth are also calcium-packed and could use extra from eggshells.
Epsom salt can improve the blooms of flowering and green shrubs, especially evergreens, azaleas and rhododendrons. Work in one tablespoon of Ultra Epsom Salt per nine square feet of bush into the soil, over the root zone, which allows the shrubs to absorb the nutritional benefits.
Moisture-loving plants like lily of the valley and marigold might tolerate coffee grounds better than plants that prefer dry soil like lavender and rosemary.
Roaches are repelled by ground coffee. In fact, putting some ground coffee down in the corners or windowsills of your kitchen can actually help keep them insects away.
A: Mosquitoes, along with other bugs and insects, hate smelly things! Coffee has a strong smell, that a lot of humans love! To our benefit, mosquitoes do not like the bitter and potent smell of coffee grounds. One man's trash is another's treasure!
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.