Coffee grounds are great for improving the soil when growing tomato plants if it is first broken down in compost. The microbes will break down the coffee and release the 2% of nitrogen from the coffee as well other nutrients such as phosphorus, iron, calcium and magnesium.
The nutrients trapped in used coffee grounds are good for tomato plants but it is best to break them down in compost before adding to your plants. Let coffee grounds break down in compost for around 6 months and then mix it through the soil.
Soil bacteria in the compost will break down the coffee grounds to release the nutrients and make them available for plants to absorb them.
If you add coffee grounds to the top of potted plants this process can be slow or will not happen at all and will not benefit your tomatoes.
Coffee grounds also contain caffeine which can actually slow tomato plant growth. Breaking coffee grounds down in compost first can help get rid of the caffeine before mixing through your soil.
Should you use coffee grounds for tomato plants?
You should use coffee grounds for your tomato plants. The best way to do this is to break down the coffee grounds in your compost pile first. Add coffee grounds to your compost mix so it makes up to 5% of the total mix.
Make sure the compost is balanced well with brown and green material. The aim is to mix 30% of the mix with green material which includes coffee grounds. Mix around 70% of the mix with brown materials including fall leaves, straw, hay or shredded dry plant material.
The microbes in the compost will break down the coffee grounds releasing the nutrients including nitrogen in a form that makes them available to the plants.
Mix the compost through your soil before planting your new tomato seedlings. This will help to lighten the soil to improve drainage, feed the plants and improve the population of soil bacteria. Adding nitrogen to your soil in small amounts will give your tomato plants a great start without reducing fruit production.
By spring you will have great leaf mold which can be used as a mulch or mixed into the soil once it has fully broken down.
How to safely use coffee grounds for tomato plants
Here are a few tips and the best ways to use coffee grounds on your tomato plants without slowing their growth or reducing tomato production.
1. As fertilizer
Coffee ground contain around 2% nitrogen as well as varying amounts of phosphorus, magnesium, calcium and iron. Breaking coffee ground down in your compost will release the nutrients and can be used to feed your tomato plant.
Coffee ground will be a gentle fertilizer and will help to improve the soil over time. Mix through your coffee ground compost each year to gradually improve your soil organically over time.
2. To acidify soil
Coffee grounds can be used to increase the acidity of your soil. Tomato plants like slightly acidic soils with a pH of 5-6.5. Coffee ground can help to reduce the pH and make the soil more acidic. Most coffee grounds have a pH ranging from 5.0-6.5.
The pH of coffee grounds can vary depending on how the coffee was grown and processed. The only way to truly know is to test the pH of the coffee you are using.
3. As mulch
Make a great coffee ground mulch by mixing small amounts through bags of fall leaves. Fill a natural bag or wire cage full of fall leaves, mix through small amounts of coffee grounds and let it break down over winter.
This leaf mold makes a great mulch for tomatoes and will be close to compost by the time you are ready to use it in spring. Cover the root zone of tomatoes with this coffee ground mulch 2-3 inches thick. This will help to stop weeds and gently feed your tomato plants at the same time.
4. Make compost to improve soil
The best thing to do with your coffee grounds to help your tomato plants to grow is to make compost with it. Add small amounts of coffee grounds to your active compost pile and mix it through. Let the grounds break down for 6 months and it will be ready to add to your soil.
Mix the coffee ground compost through your potting soil, in your garden bed or use it as a top dressing for your tomato plants. This compost can also be used to mulch your tomato plants to keep weeds away and keep moisture in the soil.
Benefits of coffee grounds for tomato plants
Here are the top benefits of coffee grounds for tomato plants.
Adds nutrients
The top benefit of using coffee grounds for tomato plant is that they will add a range of nutrients to the soil including nitrogen, iron, calcium and phosphorus. These nutrients are released as the coffee grounds are broken down by soil bacteria.
It makes great mulch
Make leaf mulch with a mix of fall leaves and coffee grounds for your tomatoes. Pop them in natural bags and let them break down over 6 months. Use this as an easy, organic mulch to keep weeds away and keep the soil moist.
Are Coffee Grounds Good for Tomato Plants? | Summary
Coffee grounds are good for tomato plants but they are best added to the soil before planting after breaking them down in compost. This will help to break down the caffeine, release the nutrients and will balance out any extreme pH levels.
This coffee compost mix is great as a top dressing for established tomato plants and can be mixed through potting soil before planting potted tomatoes.
Happy growing.
I am an accredited practicing dietitian, experienced gardener and a dedicated cook. I love writing and sharing my experience so you can learn from my successes and mistakes.