A morning coffee perks us up and makes us more productive, but what does it do for plants?
Throwing the last sip of your morning cup of joe in the sink could be depriving your beloved plants of essential nutrients. Freshly brewed coffee and the grounds you throw away could give you the most vibrant flower beds in town.
Read on to find out how coffee can benefit plants, how to use it as a fertilizer, and why you should save the dregs of your coffee maker for your garden…
Benefits of Coffee for Plants
Coffee, when used in moderation, has several benefits for plants. From improving soil quality to attracting worms, here are eight ways coffee can benefit your garden…
1. Coffee is an Excellent Fertilizer
Coffee is an excellent plant fertilizer. It’s a source of nitrogen, phosphorus, potassium (NPK), and micronutrients such as magnesium and zinc.
Using coffee as a fertilizer can provide your plants with much of the nutrients they need. It can stimulate healthy foliage and root growth. However, although coffee contains the “big three” primary nutrients (nitrogen, potassium, phosphorus) you may need to supplement with other organic fertilizers.
Related: What Plants Like Coffee Grounds?
2. Coffee Grounds Improve Soil Quality
Using coffee grounds on your plants and in potting mixes can improve soil quality. Not only are coffee grounds an excellent source of NPK, but they also improve drainage, aeration, and water retention.
Coffee grounds can be used as mulch or dug into the soil to improve soil quality.
3. Coffee Improves Soil Acidity
Coffee is slightly acidic. By watering plants with a dilute brew and/or adding used coffee grounds to the soil, you can increase the medium’s acidity over time.
Coffee grounds have many uses, not just for plants but also in other eco-friendly practices that make them a valuable household item. Their gritty texture makes them a gentle natural scrub for pots and pans. You can also use them as a deodorizer in your fridge since they can absorb foul odors.
Plants that prefer acidic soils, such as lilies, rhododendrons, and hydrangeas thrive with regular coffee supplementation. However, not all plants like acidic soils — avoid giving alkaline-loving plants such as geraniums, lavender, and dianthus too much coffee.
4. Coffee Grounds Are a Slow-Release Fertilizer
Watering plants with a dilute coffee solution provides fast-release fertilization. This can provide the plants with “instant” nutrition, but it will quickly be used up. This means the plants will need feeding regularly.
Coffee grounds provide slow-release nutrition. Adding coffee grounds to the soil will provide long-lasting nutrients that plants can use weeks after supplementation. Plants that are fertilized with coffee grounds don’t require regular feeding.
5. Coffee May Deter Garden Pests
Coffee may deter certain garden pests. Placing coffee grounds around the base of your prized flowers or vegetables may protect them from slugs and snails.
Although there’s no scientific evidence to back this up, many gardeners swear by coffee grounds. The rough texture of coarsely ground coffee, the sharp acidicness, and the caffeine content could be the reason it works.
It’s not just slugs that coffee can deter. Domestic cats can be a nuisance to gardeners, often using their flower beds as litter boxes. The strong smell of coffee deters cats, preventing them from defecating in your borders.
6. Coffee May Prevent Plant Diseases
Coffee may prevent certain fungal and bacterial infections such as leaf rust, soft rot, and blight.
Although there isn’t a huge amount of evidence supporting this, one study revealed that using coffee grounds as part of a potting mix prevents pathogenic organisms from forming [1].
The non-pathogenic fungi found on decomposing coffee grounds are believed to be responsible for the pathogen-suppressing qualities of the material. If you want to use coffee to prevent disease, make sure to use coffee grounds rather than liquid coffee.
7. Worm Attraction
For reasons unknown to science, coffee grounds attract worms. The wriggling critters love coffee grounds and will distribute them through the soil layers.
Attracting worms is beneficial for many reasons. Worms help break down organic matter, making nutrients in the soil more accessible to plants. They also aerate the soil and improve drainage.
8. Speeds up Composting
Coffee grounds are excellent for composting bins. They are considered a “green” composting material, which is high in nitrogen. The nitrogen-rich grounds help break down carbon-rich “brown” composting material, producing high-quality compost faster.
How to Use Coffee Grounds in the Garden
There are several ways to use coffee grounds in the garden. You can compost them, make potting mixes, make slow-release “coffee cakes,” or add them directly to the topsoil.
Here are four ways to use coffee grounds in your garden:
1. Feed the Grounds to Your Plants
If you have leftover coffee grounds and your plants could do with feeding, you can add them directly to the soil. Lightly sprinkle the grounds around the base of your plants or rake them into your flower beds.
2. Add Coffee Grounds to Potting Mixes
Coffee grounds make an excellent addition to potting mixes. They provide aeration, improved drainage, and slow-release fertilizing.
Potting mixes should be 4:1 (soil to coffee grounds). A good potting mix ratio is 25% coffee grounds, 25% all-purpose compost, and 50% light topsoil.
3. Make Slow-Release Coffee Cakes
Used coffee grounds provide slow-release nutrients, even when sprinkled on the soil. However, their feeding power can be prolonged further if you press the grounds into fertilizer cakes.
These cakes are placed on the topsoil. Every time the plants are watered, the coffee cake will gradually decompose, feeding the plant with nitrogen, potassium, and phosphorus.
You can make fertilizer cakes with an old muffin tin. Fill each space with freshly-used grounds and press firmly until a dense “cake” is formed. Leave the cakes to dry for one to two weeks, or speed up the process and dry them in an oven at 120 degrees Celsius for one to two hours.
4. Compost the Coffee Grounds
If you’re a heavy coffee drinker, you’ll eventually end up with more used coffee grounds than you need for your garden. Don’t waste them, though. Instead, throw them in your compost bin or pile.
Combined with organic waste from your garden and kitchen, coffee grounds make a dark, rich compost that’s excellent for enriching flower beds and starting seedlings.
How to Make Liquid Coffee Fertilizer
Using old coffee grounds is a great way to improve soil quality and provide slow-release nutrients to your plants. However, it’s not just coffee grounds that can be saved and used in your garden.
That leftover joe in your French press or drip coffee maker can be used as well. Making liquid fertilizer from leftover coffee is a great way to provide plants with NPK and other micronutrients quickly.
You can’t water your plants with straight coffee. It must first be diluted to avoid root burn and caffeine toxicity.
You want a 5:1 ratio of water to coffee. However, this may be more or less depending on the strength of your brew. Robusta coffee is stronger than arabica coffee — dilute robusta blends more.
You’re aiming for a liquid that looks like a weak black tea but this isn’t an exact science. If you think the liquid looks too strong, dilute it further — it’s better to have a weak fertilizer than an overly strong fertilizer.
How Often Should You Give Plants Coffee
Generally speaking, you should give plants coffee once per week. However, the time frame differs depending on whether you’re watering with coffee, how diluted the solution is, or using coffee grounds to enrich the soil.
When to Water Plants With Coffee
Water plants once per week with a diluted coffee fertilizer.
Some plants are more sensitive to coffee than others. You may only require bi-weekly or monthly feeding for sensitive flowers and vegetables.
If you see signs of overfeeding — yellowing leaves, wilting leaves, defoliation, or stunted growth — stop feeding your plants and switch to plain water. Once recovered, feed bi-weekly or monthly with a more diluted coffee solution.
For perennial plants that die back during the colder months, avoid feeding during dormant periods. Over-feeding in the autumn and winter can cause root burn and other negative side effects.
When to Give Plants Coffee Grounds
Coffee grounds provide slow-release nutrients, which means you won't need to feed your plants grounds as often.
If you plan on using grounds on larger flower beds, you can spread grounds regularly, as the large amount of soil will help disperse the nutrients. You have to be careful using coffee grounds in pots as regular feeding can over-acidify the soil.
Don’t feed coffee grounds to house plants, flower pots, and potted vegetables more than once every two to four weeks.
If you see signs of acidification or nutrient overload — stunted growth, dying leaves, yellowing, wilting, or twisted leaves — you may need to repot the plant to reduce acidity.
Coffee-Loving Plants
Coffee isn't a good fertilizer for all plants. Some plants love coffee, while others are sensitive to its caffeine and acidity. Most plants that prefer neutral to acidic soils will benefit from coffee. Plants that prefer alkaline soils do not benefit from coffee.
Here are some plants that thrive with weekly coffee fertilizing and/or soil enrichment with coffee grounds:
1. Flowers
These flowers benefit from coffee fertilizing:
- Roses (Rosa spp.)
- Azaleas (Rhododendron spp.)
- Hydrangeas (Hydrangea macrophylla)
- Camellias (Camellia japonica)
- Gardenias (Gardenia jasminoides)
- Magnolias (Magnolia grandiflora)
- Begonias (Begonia spp.)
- Heathers (Calluna vulgaris)
- Daffodils (Narcissus spp.)
- Hostas (Hosta spp.)
- Pieris (Pieris japonica)
- Lilies (Lilium spp.)
- Fuchsias (Fuchsia spp.)
- Clematis (Clematis spp.)
- Cyclamens (Cyclamen persicum)
- Primroses (Primula spp.)
- Violets (Viola spp.)
- Marigolds (Tagetes spp.)
2. Vegetables
These garden vegetables benefit from coffee grounds and watering:
- Tomatoes (Solanum lycopersicum)
- Carrots (Daucus carota subsp. sativus)
- Radishes (Raphanus sativus)
- Spinach (Spinacia oleracea)
- Lettuce (Lactuca sativa)
- Peppers (Capsicum spp.)
- Broccoli (Brassica oleracea var. italica)
- Cauliflower (Brassica oleracea var. botrytis)
- Green Beans (Phaseolus spp.)
- Cucumbers (Cucumis sativus)
- Potatoes (Solanum tuberosum)
- Squash (Cucurbita spp.)
- Beets (Beta vulgaris subsp. vulgaris)
- Kale (Brassica oleracea var. sabellica)
- Zucchini (Cucurbita pepo)
3. House Plants
These houseplants can be fertilized with coffee:
- Orchids (Orchidaceae spp.)
- Philodendrons (Philodendron spp.)
- Pothos (Epipremnum aureum)
- Ferns (Pteridophyta spp.)
- Spider Plants (Chlorophytum comosum)
- African Violets (Saintpaulia spp.)
- Peace Lilies (Spathiphyllum spp.)
- Jade Plants (Crassula ovata)
- Snake Plants (Sansevieria trifasciata)
- Monstera (Monstera deliciosa)
FAQs: What Does Coffee Do for Plants?
Want to learn more about how coffee affects plants?
Check the answers to the frequently asked questions below.
1. Can You Compost Coffee Grounds?
Yes. You can compost coffee grounds. Worms love grounds, and they contain several minerals, such as nitrogen, phosphorus, and magnesium, which are beneficial to plants.
2. What Nutrients Does Coffee Add to the Soil?
Coffee contains several essential nutrients that can be used as “food” for many plant species. It contains nitrogen, phosphorus, potassium, magnesium, and many other micronutrients that promote plant growth.
3. Is it Safe to Use Coffee on All Types of Plants?
Most plants will benefit from coffee but it shouldn't be given to all.
Some plants do not benefit from the acid-rich soils coffee grounds can produce when large amounts are added. Alkaline soil-loving plants like lavender and lilac shouldn’t have coffee. Some species — geraniums and certain aromatic herbaceous plants — are sensitive to the caffeine in coffee.
4. Can Coffee Be Used to Prevent Fungal Growth in Plants?
Coffee is slightly anti-fungal but these properties are so weak that it may not have a lasting effect on fungal growth in plants. With that said, some research has demonstrated that coffee grounds can suppress certain harmful organisms when used as part of a compost mix [1].
5. How Does the Caffeine in Coffee Affect Plants?
The caffeine in coffee can be detrimental to plants. It’s important to use coffee responsibly in the garden. Caffeine in concentrations greater than 0.1% can distort and damage cells, leading to poor root and foliage formation [2].
6. How Often to Water Plants With Coffee?
Plants can be watered with coffee once per week. However, it’s a strong fertilizer, and the caffeine content in strong brews can be detrimental. Always water coffee down before using it on your plants.
7. Can Coffee Grounds Get Rid of Slugs in my Garden?
Many gardeners claim that putting coffee grounds around the base of their plants deters and potentially kills slugs and snails. The acidity of the coffee and the sharp coarseness of a medium to coarse grind is likely the reason this works. However, not all gardeners agree — some claim it’s useless against the slimy pests.
8. Can You Grow Coffee At Home?
Yes. You can grow coffee at home but don’t expect a bountiful harvest if any, harvest at all. These plants like tropical climates and relatively high altitudes — conditions that most people can’t re-create. With that said, they make rewarding but demanding houseplants.
References:
- Chalker-Scott, L. K. (2016). Using coffee grounds in gardens and landscapes. Washington State University Extension.
- Muratova, S. A., Papikhin, R. V., & Khoroshkova, Y. V. (2020). The effect of caffeine in a nutrient medium on rhizogenesis of the Rubus genus plants. In BIO Web of Conferences (Vol. 23, p. 03013). EDP Sciences.
