A quick search for “Using coffee grounds in the garden” and Google will unleash a deluge of links to articles telling you to save those spent grounds!
We are advised to put them in the garden for perky plants and bright blue azaleas. Coffee grounds ward off slugs! Put coffee grounds in your compost for healthy soil and earthworms! Grow HUGE plants with coffee grounds! Some even suggest using coffee as a mulch.
It doesn’t take long to see that coffee is touted as thepanacea of the garden. Whatever you’re gardening issue is, it seems coffee canfix it.
(As a coffee-lover, I’m already convinced of the magicalproperties of coffee to bring me back to the living.)
But are coffee grounds really all that great for yourgarden?
Once you start digging into Google’s massive list ofarticles, conflicting information begins to surface. Coffee grounds are tooacidic; coffee grounds aren’t acidic at all. Coffee is terrible for yourcompost; coffee makes excellent compost, etc.
Because I love you, Rural Sprout readers, I spent a coupleof hours sleuthing on the internet to cut through the myth and bring you thetruth.
You might want to sit down for this.
But make a cup of coffee before you settle in to read. We’reabout to fall down the rabbit hole.
Here’s what I found.
Can coffee grounds acidify your soil?
Probably the most common gardening advice for spent coffee grounds is to use them to acidify your soil.
It makes sense; everyone knows coffee is acidic. There are quite a few low-acid coffee blends on the market these days. The question is, how acidic are coffee grounds, once you’ve made your coffee.
Turns out, not very acidic at all.
The Oregon State University Extension tells us that the acid in coffee beans is water-soluble. So, in the end, it’s your cup of coffee, not your used grounds that end up being acidic. Used coffee grounds come in with a pH of 6.5 to 6.8. That’s pretty basic. (Heh, pH humor.)
Sorry guys, it looks like this common practice is pure myth, spent coffee grounds are practically pH neutral.
I wouldn’t suggest putting fresh coffee grounds onplants to acidify your soil either. Yes, that’s a bit of foreshadowing, keepreading.
As we’ve already learned, the acid is water-soluble and will be washed out of your soil pretty quickly, leaving you to apply more and more coffee grounds.
But wait…
Aren’t coffee grounds supposed to make good mulch?
Nope, this perennial garden advice is busted as well.
Remember all those pucks of spent grounds you see at your local coffee shop after they’ve made your espresso shot? Coffee grounds compact too quickly which doesn’t make them an ideal media for mulch. Your mulch needs to breathe to let water and air in as well as out of the soil.
Quite a few scientists are interested in the coffee question too, as I found several scientific studies concerning the use of coffee grounds in the garden.
So are coffee grounds useful for making great compost?
Nearly as popular as using coffee to acidify your soil, is the use of coffee grounds to compost.
One study compared three different composting methods to measure the effect of adding coffee grounds to your compost. In all three methods they found an increase in the death-rate of earthworms.
Eeesh, poor little guys!
Apparently as the coffee grounds break down, they release “organiccompounds and chemicals” which kill the worms.
It would appear that coffee grounds are not so great for earthworms after all. And you need more earthworms in your soil.
And as if murdering innocent earthworms wasn’t bad enough, it appears that coffee has antibacterial properties, too.
So, instead of helping the thriving microbiota of your compost, tossing those coffee grounds in could actually kill off helpful microbes.
If you do decide to add coffee to your compost, do so sparingly. Despite its color, coffee is considered to be a ‘green’ addition, so it needs to be mixed in with plenty of ‘brown,’ like dried leaves.
What about using coffee grounds for killing slugs?
Well, if coffee is good at killing things, then surely theadvice to use coffee grounds to kill slugs or repel them is accurate, right?
This one is a big fat maybe.
Robert Pavlis of Garden Myths, set up his own experiment with slugs and coffee grounds, and he says the coffee grounds don’t even slow them down!
I read other anecdotal advice saying that slugs won’t even go near coffee grounds. While I can’t say with certainty that coffee grounds will repel slugs, in this case, it can’t hurt to try.
However, I wouldn’t put the grounds too close to the plantsyou are trying to protect.
That’s right, more foreshadowing.
Here are some ways that do work for keeping slugs away.
The #1 reason why you shouldn’t put coffee grounds on your plants
Why do I keep warning you not to put coffee grounds on yourplants?
Because as we all know, coffee is caffeinated.
As much as we like to think caffeine was created for humans, evolution had other ideas.
Science tells us caffeine was first a mutation in plants which was accidentally copied and passed on. Caffeine gave plants (think tea plants, cocoa and coffee trees) an edge over competing plants growing nearby.
How? The caffeine in these plants’ fallen leaves would “poison” the soil so that other plants nearby couldn’t grow.
Still want to put those coffee grounds on your prize tomatoes?
It’s been demonstrated in a number of studies, that caffeine suppresses plant growth. Caffeine reduces germination rates in many plants by tying up the nitrogen in the soil.
This study, in particular, cracks me up. The title of the paper tells you all you need to know, “Applying spent coffee grounds directly to urban agriculture soils greatly reduces plant growth.”
Okay, I’m sure you’re thinking, but I already brewed mycoffee, there can’t be that much caffeine left in the spent grounds, right?
Unfortunately, depending on the brewing method, yes, therecan be!
Caffeine Informer sites a 2012 study conducted by The Department of Nutrition, Food Science and Physiology, School of Pharmacy, University of Navarra showing spent coffee grounds can contain up to 8.09 mg of caffeine per gram of grounds.
With these numbers in hand, Caffeine Informer states that the average amount of coffee grounds used to brew a shot of espresso can still have up to 41 mg of caffeine. That’s nearly the same amount of caffeine that’s in a cup of black tea!
Aha!
It appears we may have finally stumbled across the best usefor coffee grounds in the garden – weed killer!
Remember, caffeine inhibits plant growth. This study conducted by the International Plant Propagator’s Society noted that using coffee grounds did result in lower germination rates. White clover, Palmer amaranth, and perennial rye were the three plants used in their study.
Perhaps a liberal sprinkling of coffee grounds on peskyweeds is just what you need to give them the boot. Or try boiling them to makea concentrated weed-killing spray.
I’m sure by now you are a little disheartened with the newsthat coffee isn’t the best thing to give you a pest-free garden with a biggeryield. Maybe you are even nervously eyeing that pile of coffee grounds youdumped in the compost bin.
You’re probably thinking, “What the heck am I going to dowith all of those spent coffee grounds now?”
Well, my friend, I’ve got good news, you can use them around the house. I’ve already got 28 great ideas for you to try.
Read Next:
How to Grow a Beautiful Coffee Plant Indoors
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FAQs
Why should coffee grounds not be used in the garden? ›
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.
Which plants do not like used coffee grounds? ›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.
Can you put coffee grounds in your garden yes or no? ›Adding coffee grounds directly to the soil as a fertiliser can be a good option. 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.
What are the issues with coffee grounds? ›Typically, spent coffee grounds are dumped into general waste and sent to landfill where they decompose and emit methane – a greenhouse gas 25 times more potent than carbon dioxide over a 100-year period, and one of the primary causes of global warming. This level of detrimental waste is a calamity in itself.
Do coffee grounds in garden attract bugs? ›Fertilize Your Garden
Spreading coffee grounds throughout your garden will also attract insects, such as, worms.
Keep Bugs at Bay
Coffee grounds are great for pest control. Ants especially don't like them - both grounds and the acids damage their exoskeletons. Use spent grounds to keep ants out of the house by laying down a 2 inch wide line around the foundation and entrances.
There are so many benefits of coffee grounds in snake plants that we can get. The soil is fertilized when coffee grounds are added to snake plants. Coffee grounds can assist in the addition of nitrogen, potassium, and other vital nutrients.
What plant benefits most from coffee grounds? ›- 1) Hortensia (Hydrangea spp.)
- 2) Azalea (Rhododendron spp.)
- 3) Highbush blueberries (Vaccinium sect. ...
- 4) Lily of the valley (Convallaria majalis)
- 5) Carrot (Daucus carota subsp.
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 I put coffee grounds in my garden? ›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.
Should you throw coffee grounds on your lawn? ›
The benefit of using coffee grounds as a fertilizer is that it adds organic material to the soil, which improves drainage, water retention and aeration in the soil. The used coffee grounds will also help microorganisms beneficial to plant growth thrive as well as attract earthworms.
Can I throw coffee grounds on my lawn? ›Coffee grounds do indeed supply essential nitrogen to the lawn, but the raw grounds may actually harm the health of the lawn soil. Put coffee grounds through the compost with shredded fall leaves or other similar dry material and then use the finished compost as a top-dressing feeding for the grass.
What animals do coffee grounds keep away? ›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.
Coffee grounds make an effective mosquito repellent because of the strong smell. The coffee grounds will mask the scents on humans that attract mosquitoes - if they can't smell you they can't find you! You can also burn it to create an even stronger aroma - the same way citronella candles keep mosquitoes away.
Why do bugs hate coffee grounds? ›Most bugs have a very strong sense of smell. Coffee grounds are very potent and even more potent once they are burned. The strong scent and “smoldering effect” will fight off pests and keep them away. Additionally, smoke is generally associated with danger, so bugs will look elsewhere for shelter.
Does coffee attract roaches? ›Roaches aren't particularly in love with coffee, but they're not known to be picky eaters either. They'll eat almost anything to get the energy and nutrients that they need to survive. So if they won't find anything else sweeter or more delectable in a cupboard, they'll definitely go for your coffee.
Do ants dislike coffee grounds? ›Repel ants
Leave coffee grounds where the ants are and they will carry it home and eat it. This method takes a few weeks to see, but after a while you'll notice a decrease of the ants population.
In sharp contrast to the advice of internet posts that suggest spreading coffee grounds to deter ants, new studies suggest that household ants are attracted to coffee odor.
Will coffee grounds keep mice away? ›The answer to this question is yes, use coffee grounds as a natural rodent repellent. The coffee's bitter compounds are unpleasant to rats and mice. They will avoid areas where there is a coffee scent or use.
Do spiders like coffee grounds? ›Because of their strong sense of smell, spiders dislike anything with a potent odor. The smell of burnt coffee grounds and citrus (or any of the above scents) will certainly be hard for them to return to.
Do termites like coffee grounds? ›
Coffee killed termites in 3.42 hrs, and Coke was the least effective (5.04 hrs). It was interesting to observe that higher the caffeine levels, the sooner the termites died.
Do plants like to be touched? ›Your plants really dislike when you touch them, apparently. A new study out of the La Trobe Institute for Agriculture and Food has found that most plants are extremely sensitive to touch, and even a light touch can significantly stunt their growth, reports Phys.org.
Which plant smell snakes hate? ›Like other varmints, snakes dislike the smell of onions or garlic. A smart way to keep them away is to plant garlic and onion plants. Snakes cannot stand the sulphonic corrosive that the onion plant produces. On the other hand, when snakes slither on the plant, garlic releases a greasy oil that irritates them.
What does cinnamon do for snake plants? ›Quick tip: Add ground cinnamon to the ends of your cuttings. "Cinnamon helps speed up the healing process and is also a natural way to help prevent issues as it is a natural anti-fungal," says Kujawa.
Which plant needs coffee? ›The plants that like coffee grounds include roses, blueberries, azaleas, carrots, radishes, rhododendrons, hydrangeas, cabbage, lilies, and hollies. You'll want to avoid using coffee grounds on plants like tomatoes, clovers, and alfalfa.
What can you do with old coffee grounds? ›- Fertilize Your Garden. Most soil does not contain the essential nutrients needed for optimal plant growth. ...
- Compost It for Later. ...
- Repel Insects and Pests. ...
- Remove Fleas from Your Pet. ...
- Neutralize Odors. ...
- Use It as a Natural Cleaning Scrub. ...
- Scour Your Pots and Pans. ...
- Exfoliate Your Skin.
Plants like tomatoes, peppers and eggplants in particular will benefit from shell fertilizer, Savio said. The extra calcium will help prevent blossom-end rot. Broccoli, cauliflower, Swiss chard, spinach and amaranth are also calcium-packed and could use extra from eggshells.
Can I use leftover coffee to water plants? ›Coffee works great on many types of flowering indoor plants but can be used outside as well. Diluted coffee adds just enough organic fertilizer to encourage bushier, healthier plants.
Do fruit trees like coffee grounds? ›Coffee grounds contain nitrogen, phosphorus, magnesium, and copper, all of which are essential to fruit trees. They also raise the pH level in the soil, which is good for the health of the plant. Most fruit trees require slightly acidic soil, so adding coffee grounds will help them thrive.
Which plants like Epsom salts? ›- Pepper plants: Peppers need extra magnesium, especially if you grow them in pots. ...
- Roses: Rose bushes benefit from the magnesium in Epsom salt. ...
- Tomato plants: While some Epsom salt can benefit vegetables and can help increase the flavor profile, too much can lead to blossom end rot.
Can you put too much coffee grounds in soil? ›
Additionally, coffee grounds, though a good source of nitrogen, are acidic, and excess acid prevents the compost heap from heating up enough to decompose. She recommends that grounds make up no more than 15 to 20% of the total compost volume.
Where is the best place to put coffee grounds in the garden? ›To use coffee grounds as a fertilizer sprinkle them thinly onto your soil, or add them to your compost heap. Despite their color, for the purposes of composting they're a 'green', or nitrogen-rich organic material.
How long are coffee grounds good for once ground? ›Most ground coffee stays fresh for about one week after grinding. With the short shelf life of ground coffee, you should always use it within two weeks of purchase to enjoy that fresh and flavorful coffee that you want.
What does Epsom salt do to lawns? ›Epsom salt is an organic compound that is full of beneficial minerals for lawns. Iron in Epsom salt, for example, helps grasses to grow healthy and strong. Meanwhile, the magnesium in Epsom salt balances the PH level in your grasses so that it doesn't become too acidic.
Do coffee grounds make grass greener? ›The results they've seen are healthier flowers and plants, and greener grass. When spread over flower beds and lawns, coffee grounds slowly release nitrogen -- a key nutrient that helps plants grow -- into the soil. The used grounds also attract earthworms.
Do coffee grounds keep squirrels away? ›Deterrent For Other Animals
Coffee grounds not only repel squirrels but other pesky critters as well. So whether you're trying to minimize the number of small chipmunks or large deer (read our article about deer and coffee grounds) in your yard, there's a chance that coffee grounds can help.
Did you know dogs detest anything bitter? To keep your dog out of your garden simply take your morning coffee grounds and mix them with a dissolved bitter orange capsule/pill. Sprinkle this mixture around the perimeter of your garden.
What pests eat coffee? ›Several insect pests have been reported in coffee, the most important being the coffee leaf miner, the coffee berry borer, and the coffee stem borers.
Does dryer sheets keep mosquitoes away? ›Dryer sheets are designed to provide a pleasant scent to laundry, not to repel insects, so any insect-repellent properties may wear off quickly. In summary, while some people claim that dryer sheets can repel mosquitoes, there is little scientific evidence to support this claim.
What smell do mosquitoes hate the most? ›A few of the best include: Lemon eucalyptus – The Center for Disease Control (CDC) has credited lemon eucalyptus oil as a reliable mosquito repellent. If you enjoy the bright smell of lemon, this oil is worth a try. Peppermint – For us, the smell of peppermint is a mark of freshness and cleanliness.
What do mosquitoes absolutely hate? ›
Mosquitoes hate the smell of lavender, citronella, clove, peppermint, basil, cedarwood, eucalyptus, peppermint, lemongrass and rosemary. They also hate smells such as smoke, for further insight, see our exploration on, does smoke keep mosquitoes away?
Do roaches dislike 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.
Do coffee grounds go in garden or compost? ›– Coffee grounds can be an excellent addition to a compost pile. The grounds are relatively rich in nitrogen, providing bacteria the energy they need to turn organic matter into compost.
Do coffee grounds keep squash bugs away? ›A simple DIY organic squash bug control method is making use of coffee grounds. Boil coffee grounds in water and let the solution cool before spraying it onto the bugs. This spray also repels cucumber beetles and other zucchini plant bugs.
What vegetables like coffee grounds and eggshells? ›Plants like tomatoes, peppers and eggplants in particular will benefit from shell fertilizer, Savio said. The extra calcium will help prevent blossom-end rot. Broccoli, cauliflower, Swiss chard, spinach and amaranth are also calcium-packed and could use extra from eggshells.
Do coffee grounds attract rats? ›Rat - Wikipedia
and mice are attracted to food odors, they aren't interested in the smell or taste of coffee grounds. In fact, both used and fresh coffee grounds repel mice and rats.
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.
How long does it take for coffee grounds to decompose? ›Coffee grounds take three to four months or more to decompose, depending on the soil microbial activity and health. The more microbial activity of the soil, the more quickly coffee grounds decompose.
What animals hate coffee grounds? ›“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.”
Does coffee keep mosquitoes away? ›Coffee grounds make an effective mosquito repellent because of the strong smell. The coffee grounds will mask the scents on humans that attract mosquitoes - if they can't smell you they can't find you! You can also burn it to create an even stronger aroma - the same way citronella candles keep mosquitoes away.
What insect eats coffee grounds? ›
The beetle is the only animal that can feed solely on coffee beans. Others might occasionally nibble the seeds or other parts of the coffee plant, but they don't dedicate themselves to the task.
Why put a raw egg in coffee grounds? ›Adding the egg helps clarify the coffee, allowing the grounds to separate from the water easily. The egg white extracts the bitterness from the grounds and enhances the caffeine. The result is a light, clear brew with absolutely no bitterness or acidity and a velvety texture that's easy to drink.
Which vegetable plants benefit from coffee grounds? ›Coffee grounds as a fertilizer can be used when growing vegetable crops such as potatoes, cucumbers, peppers, carrots, radishes, and beans. Root crops need magnesium and potassium, while nitrogen is indispensable for green crops.
How was Cowboy coffee made? ›Cowboy coffee is a traditional drink made by cowboys on the trail. It's brewed by heating coarse grounds with water and then pouring it into a cup after the grounds have settled.