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.
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.
While many budding gardeners may be concerned that coffee grounds can attract pests, the reality is quite to the contrary. In fact, when implemented correctly, coffee grounds can be an effective way to repel certain pests such as wasps, snails, and mosquitoes.
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.
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.
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.
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 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.
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.
When repotting plants, thoroughly mix in a quarter cup of grounds for every 4 to 6 cups of potting soil. By blending it into the soil, it will release its power slowly. All without the worry of clumping together and holding too much water in place around roots.
As we mentioned, coffee grounds work best on plants that require acids, but they can also be of benefit to those that do not adore them. Used in moderation, they will still help attract earthworms that help turn and aerate the soil.
Eggshell Benefits
As it happens, eggshells can provide all the calcium carbonate the soil needs, which helps to lower the soil's pH level and make it more alkaline as opposed to acidic. This is incredibly beneficial for plant growth because many plants prefer to grow in soil that has low acidity.
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.
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.
Coffee grounds will keep squirrels away from your garden because they do not like the smell. Simply sprinkle some fresh grounds on the soil surrounding your plants every two weeks. You can also try spraying your plants with a hot pepper spray for the same effect.
Worms love to eat coffee grounds, and that's great news for your garden. Add coffee grounds to your compost pile to help attract worms, which help speed up the process of turning food scraps into compost. You can also add coffee grounds directly to the soil, but you'll have to be careful not to overdo it.
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.
Smells that roaches hate: a quickfire summary
Oregano, rosemary, mint, eucalyptus, lemongrass and catnip are great herby options. Citrus oils work brilliantly too. And surprisingly, lower concentrations – 2.5 parts per hundred – seem to work best as deterrents. Just don't bother with lavender.
Roach Repellents
Peppermint oil, cedarwood oil, and cypress oil are essential oils that effectively keep cockroaches at bay. Additionally, these insects hate the smell of crushed bay leaves and steer clear of coffee grounds. If you want to try a natural way to kill them, combine powdered sugar and boric acid.
Sugar is by far the most attractive substance to a cockroach. They love sugar and can smell it from anywhere. This means you'll want to keep your sugar containers, fruits, and other sweeteners sealed in air-tight containers that are up off the floor.
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.