Yes, coffee grounds are good for plants in moderation. Used grounds add organic matter and a little slow-release nitrogen, and they attract earthworms. They’re close to neutral pH, so they won’t acidify soil. Mix them into compost or soil in thin layers, because thick layers can form a crust, block water, and grow mold.
Below, we separate the facts from popular garden myths, list which plants love coffee grounds and which ones they can harm, and show four safe ways to use them: compost, mulch, fertilizer, and pest control.
Is Coffee Good for Plants?
Used coffee grounds are good for soil, not as a fertilizer. According to Oregon State University Extension, they contain only 1–2% nitrogen and trace minerals, too little to feed plants alone. Their real benefit is better drainage and soil structure as microbes break them down. Used grounds have a pH of about 6.5–6.8, so they won’t acidify soil. Too much can slow seed germination and growth because of leftover caffeine.
Ways To Use Coffee Grounds in the Garden
Gardeners began to use coffee grounds in planting quite recently. And only a few people know about this unique and useful substance. We have compiled a list of the best ways to use ground coffee to benefit your plants.
Using Grounds as a Natural Nitrogen Fertilizer
If your plants need nitrogen fertilizer for garden, have a look at coffee. Coffee grounds are valuable as a fertilizer for plants containing nitrogen and other elements. In its nitrogen content, coffee grounds are equal to grass clippings.
It's hard to overstate the importance of nitrogen for soil, especially for plants, for which nitrogen is a vital element. Nitrogen leads to faster plant growth, strengthens the stem, and helps in chlorophyll production. Therefore, natural nitrogen for plants becomes an excellent fertilizer. Used coffee is also an excellent source of nitrogen for composting. It contains about 2% of this element, and with the right proportions, you can make great compost.
Remember, If you use coffee grounds as fertilizer, it is essential to follow proper watering techniques. The soil must dry out well to prevent the appearance of mold.
Using Coffee Grounds as Mulch
Coffee grounds are also used for mulching to prevent the soil from drying out, protect against pests, and improve soil quality. You can mulch both houseplants and garden plants in the open ground. Cover the soil around the plant's trunk with well-dried coffee grounds and water abundantly. Each watering will release nitrogen from the coffee grits and penetrate into the soil with water, soaking the plant's root system, thereby strengthening it and protecting it from pests.
Composting with Coffee Grounds
Compost is the most effective organic fertilizer for plants. It is suitable for the orchard or vegetable garden and for nourishing house plants.
Ground coffee is added to compost to speed up the process of maturation. They act as nitrogen compounds that start an exothermic reaction in the compost heap, which warms it up considerably and thereby ripens the compost much more quickly.
How to Compost Coffee Grounds
Start composting by calculating the right amount of coffee grounds and other ingredients. You can often vary the composition, but an optimum mixture is 50 % coffee grounds, 30 % straw, and 20 % leaves.
Prepare a compost pit or large tank, which should be placed in the most protected place from rain and wind.
Place coffee grounds, straw, and leaves or dried grass in the same pile.
Coffee grounds should be well mixed and covered with fertile soil.
Water the compost to make it a little wet and make a few holes to create a microclimate inside.
Your compost will be ready in 3-4 weeks. After that, it can be used as a fertilizer for houseplants and garden plants.
Coffee Grounds as a Pesticide
Coffee grounds can be used as a perfect protector against pests. Ants, snails, slugs, and many other insects do not like coffee grounds, which means they will avoid your garden beds. In the opinion of many gardeners, coffee can also kill the larvae of pests, particularly mosquitoes and garden bugs. Coffee grounds are not as effective as insecticides, but one of the clear advantages is their non-toxicity.
What Plants Like Coffee Grounds
As an organic nutrient, coffee grounds are suitable for most plants. However, since coffee slightly acidifies the soil, it is beneficial for roses, hibiscuses, begonias, and other plants prefer substrates with an acidic or slightly acidic reaction.
Before diving into the specifics, take a look at this visual guide to some popular plants that thrive with coffee grounds—it might surprise you!
What Vegetables Like 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.
Onions
For non-commercial purposes, onions are advised to grow only on organic fertilizers. The main valuable component for onions is nitrogen. If you fertilize green plants, such as lettuce and spinach, with a coffee substrate, the yield will be higher due to the nitrogen content of coffee. Adding coffee grounds to soil only benefits onion and green cultures.
Potatoes
The most important period in the potato life cycle is the budding and flowering phases. The nitrogen, phosphorus, and potassium consumption reaches its peak, and the plant needs to be fertilized. This is when coffee containing these nutrients comes in handy.
Carrots
Carrots like fertile soil with a neutral pH, loose and breathable, which coffee grounds can provide. Also, carrots prefer decomposed fertilizers, so use ready-made compost with coffee grounds or humus to fertilize them.
Are Coffee Grounds Good for Flowers?
Flowers are especially fond of coffee grounds. Shrub roses and begonias root much better and develop harmoniously after feeding with coffee grounds. Such fertilization is suitable for peonies, lilies, hostas, tulips, etc.
Roses
Coffee grounds can protect rose plants from pests due to their high potassium content. After coffee treatment, the flower becomes less attractive to them. Once the grounds are put in the soil, it becomes lighter, making the airflow to the roots easier. Soil rich in nitrogen, phosphorous, magnesium, and potassium is vital when growing roses from cuttings.
Interesting fact: by fertilizing roses with grounds, you can achieve a change in the color of the flower.
Hibiscuses
Coffee grounds are an organic, non-toxic fertilizer containing all the necessary microelements for hibiscus. Feeding the plant in the spring and winter can be monthly with coffee grounds, which contributes to prolonging the flowering period.
Begonias
Begonias love the addition of phosphorus-potassium and nitrogen to the soil, so coffee is an excellent substitute for chemical fertilizers. Coffee grounds help them develop buds and inflorescences.
Which Plants Do Not Like Coffee Grounds?
Some plants tolerate an acidic environment very well, but there are also those for which the acid will be poison. Plants such as sago palm, yucca, etc., will not become friends with coffee grounds.
Lavender
This plant needs an alkaline environment for growth and good flowering. For fertilization, you can use potassium products and beware of nitrogen ones. Therefore, coffee grounds are not suitable fertilizer for lavender and can lead to its death.
Orchids
Coffee grounds are too acidic for epiphytes, so their roots can rot, and mold will appear on the surface, which can attract the attention of mosquitoes. Although coffee contains enough nitrogen that orchids need, their roots do not absorb it, leading to rotting.
Rosemary
Rosemary needs fertile, loose soil with a neutral pH. The plant does not like acidic soils and overwatering, so coffee, which creates an acidic environment, will be destructive for rosemary. The plant can be nourished twice a month with mineral and organic fertilizers that create an alkaline environment.
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. Do not forget that before adding it to the compost, the ground should be dried to prevent mold formation.
FAQ
What plants like coffee grounds?
Plants that like coffee grounds include roses, leafy greens, hydrangeas, and most perennials and heavy feeders. They benefit from the organic matter and slow-release nitrogen. Compost the grounds first or mix them thinly into the soil.
What plants don’t like coffee grounds?
Plants that don’t like coffee grounds include seedlings, lavender, rosemary, succulents, and cacti. Leftover caffeine can slow seed germination and early growth. Grounds also keep soil damp, which can rot the roots of plants that prefer dry soil.
What do coffee grounds do for plants?
Coffee grounds mainly improve soil structure, so the soil drains better. They also add organic matter, attract earthworms, and release a little nitrogen as they break down. They aren’t a complete fertilizer, so keep feeding your plants as usual.
How do you use coffee grounds in the garden?
To use coffee grounds in the garden, mix half an inch of grounds into the top 4 inches of soil. You can also add them to compost, as long as they make up 20% or less of the pile. Don’t leave a thick layer on top.
Are coffee grounds good for tomato plants?
Coffee grounds are only mildly good for tomato plants: they improve the soil but don’t replace tomato fertilizer. Mix composted grounds into the bed before planting. Don’t pile them around stems, because damp grounds encourage fungal disease.
Are coffee grounds acidic?
No, used coffee grounds aren’t acidic. Their pH is about 6.5–6.8, close to neutral, because brewing washes most of the acid out. They won’t lower soil pH enough to help acid-loving plants like azaleas or blueberries.
Are coffee grounds good for houseplants?
Coffee grounds are good for houseplants only in small amounts. In pots, grounds stay damp and can grow mold or attract fungus gnats. Mix a little composted grounds into fresh potting mix when you repot instead of sprinkling them on top.
Do coffee grounds keep slugs away?
Dry coffee grounds barely affect slugs, but brewed coffee does. A soil drench of 2 parts strong coffee to 1 part water, about 1–2% caffeine, drove slugs out of treated soil in Oregon State research.
