You may want to change your mind next time you plan on just throwing away your used coffee grounds in the garbage. Because you’re not the only one who can use a cup of joe, your garden would love one too!
While using used coffee grounds in the garden is not exactly the newest gardening hack around, many people still seem to not know its benefits and proper usage. For example, did you know that not all plants will appreciate being exposed to used coffee grounds?
In some cases, it can even cause stunted growth when given to the wrong set of plants. So it’s highly important to know which plants like used coffee grounds.
Acid-loving plants are your best bet when it comes to used coffee grounds. Plants that thrive and prefer acidic soil like azaleas, hydrangeas, blueberries, and carrots will be happy for the boost that your spent coffee grounds will give them.
But that’s not all! Keep reading to know more about the perks of used coffee grounds and how to properly use them in your garden.
Can you put too many coffee grounds in your garden?
Coffee grounds are full of essential soil-friendly nutrients like nitrogen, potassium, and phosphorous. In typical garden-speak, adding organic material—like coffee grounds—sounds like a good idea. Bacteria will feed on them and break them down into nutrients your plants will need.
Plus they’re good for compost and works well as a sort of slow-release fertilizer. I know that reading this just makes you want to pour them all over your garden.
However, even in gardening—too much of anything can be simply too much.
This is what Kit Smith, a Gardening Expert in El Dorado County, tells UC Agriculture and Natural Resources. She warns gardeners that “adding unlimited coffee grounds to the compost pile is not a good practice.”
See, coffee grounds contain the pulp, hulls, and effluent of the coffee bean itself. Although this makes them an excellent source of nitrogen, this also means that they are acidic. And excess acid will eventually hinder your compost heap from heating up enough to decompose and break down.
To help you make most of your used coffee grounds without compromising the health of your plants and overall soil quality, I’ve compiled a list of things you can do with them down below. Treat this as a sort of cheat sheet for all your coffee-ground-gardening needs.
Applying Used Coffee Grounds in the Compost
- Make sure to adjust the number of coffee grounds you’ll incorporate on your compost pile so that it would make up no more than 15 to 20% of the total compost volume.
- You can incorporate the coffee grounds into the compost pile by layering the ingredients this way: 1/3 leaves, 1/3 fresh grass clippings, and 1/3 coffee grounds.
- If you are adding spent coffee grounds as part of a static compost pile, make sure to always incorporate an equal amount of carbon source into the mix. The following are good examples of carbon sources you may already have at your disposal: cardboard, dry/shredded leaves, shredded paper, hay or wood chips. Once both equal parts are added, mix thoroughly.
- When it comes to the compost bin, there are two types of compost material—brown and green. Coffee grounds fall under the green category. So when putting coffee grounds in the compost bin, make sure to balance with brown compost material. A 4-to-1 ratio of brown compost material (dry leaves, paper, etc.) to green compost material (coffee grounds) works splendidly.
- If your compost pile is starting to smell, that indicates that you’ve put too much green material. And when your compost pile won’t heat up, that means you didn’t put enough. Make sure to adjust the number of coffee grounds to the appropriate amount so you’ll end up with a working compost.
- Your compost will be ready for use once it appears like any soil and has an earthy smell. Normally it takes about three months or longer for any compost to fully break down and appear as such. This will depend on the materials that you’ve used.
Applying Used Coffee Grounds Directly into the Soil
- When incorporating coffee grounds directly into the soil, make sure to add a nitrogen fertilizer at the same time. Contrary to popular belief, coffee grounds are NOT a nitrogen fertilizer. They do, however, encourage the growth of microorganisms in the soil. These microorganisms then use nitrogen to breakdown the coffee grounds into essential nutrients your plants will benefit from.
- That’s why it’s best to pair them with nitrogen fertilizer, so while your spent coffee grounds are being broken down by the microorganisms, the nitrogen fertilizer will then provide a steady source of nutrients for your plants in the meantime. The nitrogen fertilizer also speeds up the decomposition of the coffee grounds.
- Spread the moist coffee grounds evenly in a 1-inch layer on the soil. Add the nitrogen fertilizer while making sure to follow the package directions. This nitrogen fertilizer from Amazon is one of my go-to fertilizers, so you might want to give it a try.
- Once both incorporated into the soil, mix thoroughly with a shovel or a pitchfork. See to it that the coffee grounds aren’t left on the surface level. If possible, they should be tilled into the soil to a depth of 6 to 8 inches.
Using Used Coffee Grounds as Mulch
- Due to the acidic properties of coffee grounds, they make excellent acid mulch. The best way to use them as such is by applying the coffee grounds in limited amounts. As always, there’s such a thing as being too much.
- Apply a thin layer of used coffee grounds making sure it’s not thicker than half an inch.
- When cultivated to the soil and are left to dry out, its ability to repel water is up to par with dried peat moss.
Are coffee grounds good for plants and trees?
The short answer is yes but it depends. As mentioned before, coffee grounds have a number of soil-friendly nutrients like nitrogen, potassium, and phosphorus that your plants will surely appreciate.
Both potassium and phosphorus help in plant metabolism and root development. Phosphorus also helps in flowering while potassium aids in building plant stress tolerance.
But their acidity, as well as their nitrogen content, makes them not that pleasing for every plant in your garden.
First, let’s address the nitrogen content. Nitrogen, for the most part, aids in plant growth—largely associated with leafy plants and vegetation. However, when the soil is already high in nitrogen content and you add coffee grounds into the mix, it may only result in the stunted growth of your plants.
Too much nitrogen may block other nutrients from being absorbed by your plant resulting in the aforementioned stunted growth as well as bitter-tasting fruits and vegetables.
Next is acidity. If you are itching to use your used coffee grounds in your garden, you need to make sure that you’re using it on the right plants and trees.
There are what we call acid-loving plants in gardening. And these plants are what you should focus on when using spent coffee grounds. These plants prefer their soil to be slightly acidic.
Plants that thrive in areas with lots of rainfall, also typically like their soil acidic in nature since rain can wash nutrients out of the soil.
Now that we’ve cleared that out, take a look at some of the acid-loving plants and trees that will absolutely appreciate some used coffee grounds!
- Wild strawberry
Just make sure you apply and use the coffee grounds the proper way. I personally prefer using them in the compost, so may want to start with that for a safer bet. Otherwise, enjoy playing with your used coffee grounds in your garden!
Do coffee grounds attract rats?
Rats are one of the most notorious pests every gardener will, unfortunately, meet one way or another. If you’re looking for easy and natural pest repellents to keep them away, I’m sorry that coffee grounds won’t help you in that department.
But at least they don’t attract them as well.
It is true that their nitrogen content makes them unappealing to rats but not to the point where they can deter them away.
But you can always try other natural repellents such as spraying Peppermint Oil or Eucalyptus Oil, spreading predator urine around the garden and adding chili pepper flakes in the compost.
Do coffee grounds keep bugs away?
When it comes to gardening, there are tons of tips and tricks you can find online but which ones should you actually follow? One of these, of course, is the pest repellant quality of coffee grounds.
There are all sorts of claims on the internet that coffee grounds deter slugs, snails and ants but there is still no solid research that backs this belief. There is however an experiment that showed coffee grounds decreased the amount of slug and snail activity in a cabbage plant.
Note decreased, but not deterred.
And this other experiment, albeit informal, that shows slugs do not mind the coffee grounds at all.
Do coffee grounds repel ants?
This is another claim that is verging on myth. There aren’t enough studies to back this claim although there is an experiment that used coffee grounds as an insecticide against fire ants that showed somewhat positive results however the researcher still recommends that a more detailed study should be conducted.
There is another experiment that you might want to check out. This one is informal but the result that the researcher got is as follows: “It is clear that ants do not like coffee grounds, but they don’t seem to mind the coffee itself.”