Does Mint Like Coffee Grounds? (Pros and Cons)


Like everyone else, you love to save a few bucks when you can, and if you can minimize waste while at it, that’s even better and dandier. Maybe that’s why you’re entertaining the idea of using coffee grounds on your mint plants. But does mint love coffee grounds?

Yes, you can use coffee grounds as composting feedstock, mulch, and fertilizer for your mint. It enhances soil quality and provides nitrogen and other nutrients that boost growth. Plus, it can acidify the soil, control diseases, and keep off pests.

Sure, coffee grounds can do wonders for your mint. However, if you’re not too careful, they can retain excess moisture, which spells trouble for your plant.

Today, I’m going to show you how to properly use coffee grounds on your mint without causing damage to your precious plants.

Are Coffee Grounds Good for Mint?

At the heart of why gardeners use coffee grounds to fertilize is because they’re chock-full of nutrients. The most abundant nutrient is nitrogen, which accounts for roughly 2% per volume of coffee grounds. (Source: University of Wyoming)

Nitrogen – Coffee grounds readily and gradually release nitrogen that mints require for healthy growth. It’s the cornerstone nutrient for growing new leaves and stems. Don’t forget nitrogen is an essential component of chlorophyll, which helps your mint photosynthesize and makes foliage green.

Potassium – This nutrient makes up around 0.6% of the coffee grounds per volume. Potassium helps your mint grow healthy roots and tolerate various stresses, such as low light, underwatering, or heat.

Phosphorus – A small amount of nutrient P (approx 0.06% per volume) is found in coffee grounds. It’s essential for developing roots and flowers.

Coffee grounds are also jam-packed with other beneficial micronutrients like copper, magnesium, boron, zinc, calcium, and iron. They all promote the steady, robust growth of your mint plants.

How Much Coffee Should You Add to Your Mint?

You should use coffee grounds sparingly on your mint. The composition of coffee grounds shouldn’t exceed five percent of soil volume. If you add too much, it may inhibit the growth of your mint.

In fact, according to Barnyards & Backyards at the University of Wyoming, you must use less than ½-inch of the grounds when you add directly on the soil.

If you use too thick a layer of coffee grounds, they’ll compact and affect the absorption of water. You might also end up hindering soil aeration.

How Often Should I Put Coffee Grounds on My Mint?

When you need to add coffee grounds to your mint, it should be an occasional thing. In fact, you should stick to the usual fertilization routine for your mint if you’re putting it as fertilizer.

That means you should put coffee grounds generously in early spring as your plants kick off new growth. From then on through summer, you should fertilize with coffee grounds after every four to six weeks.

Best Way to Use Coffee Ground on Mint

Composting with Coffee Grounds

Compositing is hands down the best and safest way you can use coffee grounds on your mint. Toss them together with the paper coffee filters onto the bin or pile as green compost feedstock.

Make sure coffee grounds contribute no more than 20% of the total compost volume. If you exceed that limit, you might prevent the compost from heating up enough to activate microbes that break down organic matter to release nutrients. 

Some experts suggest that you mix one part coffee grounds and four parts shredded foliage and/or sawdust by weight.

If you’re worried about the acidity of coffee dreg or grounds, simply add a little wood ash or lime to the compost blend to offset that.

Coffee Grounds as Organic Fertilizer

You can apply coffee grounds directly to the soil as fertilizer. This will help release nitrogen as well as magnesium, phosphorus, potassium, copper, and other nutrients. Your mint will love these in small doses, so don’t overboard.

You can scratch the coffee grounds into the top one or two inches of soil. Alternatively, you can spread on top of the soil and let them do their magic. It’s best if you use them during the high growth season, from early spring through summer.

Mix with Mulch

When you use coffee grounds as part of the mulch, make sure to spread a thin layer of no more than ½-inch thick on top of the soil. Using coffee ground mulch thicker than that will compact and form a barrier that will lock out much-needed water and air.

Don’t forget to cover with organic matter like compost, wood chips, shredded leaves, or shredded bark. This organic matter cover should be two to four inches thick.

Add Coffee Grounds to the Potting Mix When Repotting

Mint prefers well-drained, loose-textured mineral soils with a little bit of organic matter. For this reason, you can work on coffee grounds directly into the soil when repotting. The same is true of transplanting.

The good news about coffee grounds is that they release nutrients slowly. That means you can expect your mint to get a gradual dose of nitrogen and other nutrients. As part of the potting mix, they can feed your mint plants for up to six months.

However, you must apply the coffee grounds with a fast-acting, water-soluble, or liquid fertilizer. This will provide nutrients to the plant as microbes work on the coffee grounds.

Coffee Grounds as Compost Tea

You must first prepare compost or fertilizer “tea” from coffee grounds. Simply mix five gallons of water (preferably distilled or filtered) and two cups of spent coffee grounds.

You should allow the concoction to steep and blend overnight or at least several hours. You can then use compost tea to fertilize your potted or garden mints.

You can also use “coffee ground tea” as a homemade foliar feed. All that you have to do is spray the concoction on the foliage. Your mint will smile in bright green foliage.

Water after Application

It’s a wise idea to water your mint after applying coffee grounds directly to the soil. This will serve three purposes: 

  1. Your plant may be thirsty
  2. Water will help drive organic particles in the coffee ground down into the potting mix, and 
  3. Water will help dissipate some caffeine that may hurt your plant.

You will find that it’s best to water your mint early in the morning. This will allow it to absorb enough moisture and nutrients before the hotter sun arrives.

Use Drip Feeding Method

You can use the drip-feeding technique once you have concocted your compost tea.

– Using Water Bottle for Drip Feeding

You’ll need tape, two pieces of wood, and a sturdy water bottle.

  • Use tape and wood pieces to hold the bottle upside down
  • Create a lip from the bottom end of the bottle
  • Create a drip hole on the top lid of the bottle
  • Pour some “compost tea” from the bottom

Let the tea drip from the bottle to your mint. It should take around one to two days to drain out.

– Using Rope for Drip Feeding

You’ll need a thin wicking rope and a bucket.

  • Elevate the bucket and pour compost tea into it
  • Make sure one end of the rope is in the bucket and the other is slightly dug into your mint’s soil
  • The compost tea will flow from the bucket to your mint via capillary action.

Don’t Use Coffee Grounds on Seedlings

You might want to steer clear of coffee grounds when it comes to your mint seedlings. The acidic nature and presence of caffeine may hinder the germination and growth of your seeds or seedlings.

Moreover, coffee grounds contain organic particles that may form a cement-like layer that doesn’t allow water or air to pass.

Benefits of Using Coffee Grounds

Deter Pests

Coffee grounds have for many years been used to keep certain pests at bay from plants. This is especially true for snails, slugs, and other pests that may pester your mint in containers or gardens. How so?

One of the theories is that caffeine and other compounds in coffee adversely affect these bugs. Let’s not forget that they’re also abrasive. As such, they tend to shy away from soil that contains coffee grounds.

Coffee grounds also act as a binding agent for most chemical and organic pesticides. This helps kill and prevent pests for longer.

Prevent Diseases

As with pests, diseases often are attracted to unhealthy mint plants that are either stressed or weakened. Coffee grounds stave off diseases in a number of ways.

First of all, it’s a great source of nutrients that keep your mints healthy. More so, it fights off pests that can cause diseases or weaken your plant.

Fungal and mold colonies in decomposing coffee grounds help prevent the growth of pathogenic bacteria and fungus species. These are the pathogens that cause wilts and rots, such as Sclerotinia, Pythium, and Fusarium.

Improves Soil Quality

Coffee grounds are an excellent soil conditioner. Organic matter found in them doesn’t just improve soil structure. It also boosts water flow, especially when mixed with a range of other organic materials.

More importantly, coffee grounds are rich in nutrients that boost your plant’s potting mix and compost. Certain studies have shown that the amount of nitrogen (by volume) is about 2%, although others suggest it can be as high as 10%. (Source: Oregon State University)

Either way, nitrogen is essential for foliage growth. Coffee grounds can boost soil levels of copper, magnesium, potassium, phosphorus & iron.

Water Retention Capacity

As organic matter, coffee grounds improve the water retention capacity of the soil dramatically. In fact, if you use more than five percent per soil volume, they can create a barrier to aeration and moisture.

Improves Drainage Capacity

As with most potted plants, mints detest soggy, poorly-drained soil. They need loose-textured soil so that the roots can penetrate easily. Thankfully, coffee grounds have plenty of organic material that improves drainage capacity.

This will help prevent water from logging in the soil. In turn, this will help prevent your plant’s roots from drowning and rotting.

Keeps Pets Away

Though controversial, most people use coffee grounds on the potting soil to keep pets away, especially cats. They hate the taste and smell of caffeine, so it’s an excellent cat repellent.

Increases Soil Acidity

Mint plants thrive in slightly acidic PH between 5.5 and 6.5 (others recommend 6.5-7.0). Lucky for you, coffee grounds can acidify your potting soil. Be sure to test the pH level of your soil first.

Problems with Using Coffee Grounds on Mint

Promotes Fungal Growth

As we’ve mentioned, coffee grounds contain organic matter that retains moisture. In fact, a thick layer of the grounds will compact, creating a moist silo that encourages the growth of anaerobic fungi.

Because of the moisture, acidity, and high-nitrogen conditions, you may also spot mold, mildew, and other fungal growths. Add chunks of other organic materials to avoid this.

Excess Moisture Retention

Coffee grounds boast some fine organic particles like clay. When used as mulch, these may compact and form a cement-like barrier that retains moisture inside the soil. This will also prevent air and water from passing.

Attract Pests

It’s true that coffee grounds will deter some pests, particularly snails and slugs. However, it may create ideal conditions that attract other insects and pests.

This goes to prove that it’s best to compost with coffee grounds rather than use them directly to fertilize your mint.

Can Inhibit Growth of Mint

If your potting mix already has an adequate amount of nitrogen, adding coffee grounds will stunt your mint. Also, the caffeine present in the ground will be absorbed with water. 

Once in the system, the compound will inhibit the growth of your mint, especially younger plants and seedlings.

Potential Risks to Soil

Your mint prefers slightly acidic soil. On the other hand, coffee grounds can be highly acidifying. So, if the soil is already adequately acidic, adding coffee grounds may not be a good idea.

Watering with Leftover Coffee?

I hate to pour down cold, stale coffee down the drain. If you hate to waste, you’re probably wondering if you could water your mint with leftover coffee.

You’d be right on the money. Your mint likes slightly acidic soil. So, watering with leftover coffee will bode well with it.

Final Thoughts

  • Coffee grounds are good for your mint – it improves soil quality, acidifies the soil, and enhances drainage capacity.
  • It’s best to compost with coffee grounds rather than apply directly as fertilizer
  • Avoid using coffee grounds on seedbeds and seedlings. They’ll inhibit their growth.

Arifur Rahman

I'm the owner of gardenforindoor.com. After completing my bachelor of science in agriculture, I'm serving as a civil service officer at the Department of Agricultural Extension, Bangladesh. I started Garden For Indoor to make your indoor gardening journey easy and enjoyable.

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