Are Coffee Grounds Good for Tomato Plants? Yes and no.

Ever wondered if tossing those leftover coffee grounds onto your tomato plants is actually worth it? Well, you're not alone. I was teaching a beginner gardening class at our local library a few weeks ago, and this very question came up. I know there are a lot of myths out there when it comes to gardening, and sometimes it can get confusing. I'm going to help you out if you've ever wondered, "are coffee grounds good for tomato plants?"

Jump to:

• Do tomatoes like coffee grounds?
• Are Coffee Grounds Good for Tomato Plants?
• What Research Says About Spent Coffee Grounds
• Not all coffee is created equal
• Benefits of Coffee Grounds for Tomato Plants
• Disadvantages of Coffee Grounds for Tomato Plants
• Ideal Soil PH for tomatoes
• Signs tomatoes are benefiting from added coffee grounds
• How to add coffee grounds to the garden
• Other kitchen scraps that can be used in the garden?
• My favorite amendments for tomatoes
• Making Compost for Tomatoes
• Frequently Asked Questions
• MORE GARDENING POSTS YOU'LL LOVE
• Comments

Are Coffee Grounds Good for Tomato Plants?

Short answer, yes, coffee grounds can be beneficial for tomatoes. Coffee grounds are packed with nutrients that tomato plants love, like nitrogen, potassium, and phosphorus. They help improve soil structure and promote microbial activity, which can lead to healthier, more robust tomato plants. Plus, they may even help deter certain pests. It's like giving your juicy tomatoes a natural pick-me-up!

Now here's the caveat: While coffee grounds can be beneficial, there are a few things to watch out for. First off, they can make your soil more acidic over time, which might not be ideal for all plants. Also, if you use too many coffee grounds, it could potentially harm your tomato plants or attract unwanted pests.

Moderation is key! Don't get in the habit of emptying your coffee maker basket over the same spot every day. Once is fine and beneficial, but doing it repeatedly is going to have negative consequences.

It's also a good idea to conduct a soil test to determine the pH level of your soil before adding coffee grounds. This will help you adjust the application accordingly to ensure optimal growing conditions for tomatoes.

Before adding amendments, make sure curled tomato leaves are not caused by herbicide drift.

What Research Says About Spent Coffee Grounds

One reason there is so much conflicting gardening advice online is that many people confuse brewed coffee with spent coffee grounds. The brewing process removes many of the acidic components found in coffee beans, leaving behind spent grounds that are much closer to neutral than many gardeners realize.

Scientific studies suggest that coffee grounds are most beneficial when used as a compost material rather than applied heavily around plants. While coffee grounds contain nitrogen-rich proteins and trace amounts of essential plant nutrients, those nutrients are not immediately available to tomato plants. Instead, soil microbes must first break down the organic matter through the natural composting process.

This is why many gardeners see better results when coffee grounds become part of a healthy compost pile instead of being used as a thick top dressing around plants. Once composted, coffee grounds can help improve soil structure, increase organic matter, and contribute to healthy soil that supports strong root growth.

In my experience, the biggest difference is fresh grounds versus composted grounds. A small amount of composted coffee grounds mixed into garden beds is very different from repeatedly dumping fresh coffee grounds around the base of tomato plants. While composted grounds can be a valuable soil amendment, excessive layers of fresh grounds may create a dense surface that can interfere with soil moisture, airflow, and overall soil quality.

For most home gardeners, the best way to incorporate coffee grounds is to add them to a compost pile along with other brown materials and organic matter. Over time, the finished compost becomes a healthy mix that can be worked into the tomato garden to improve soil health naturally.

Not all coffee is created equal

And one more thing, remember that not all coffees are created equal when it comes to gardening. Generally, any type of coffee grounds can be used, but some coffee beans may be a better food source for tomato plant growth than others.

For example, organic, unflavored coffee grounds are typically the best choice, as they contain fewer additives and chemicals.

Avoid using flavored or artificially processed coffee grounds, as these may not provide the same benefits and could even harm your plants. 

Disadvantages of Coffee Grounds for Tomato Plants

Fresh coffee grounds, while generally beneficial for plants like tomatoes, can inadvertently increase the risk of fungal diseases in the soil if not applied correctly. One way this can happen is through their moisture-retaining properties. Coffee grounds have a tendency to hold onto moisture, creating a damp environment that promotes the growth of fungi, including harmful ones that cause diseases like mold or fungal rot. 

Additionally, while coffee grinds are slightly acidic, which can be beneficial for some plants, excessive acidity can also create conditions favorable for certain fungal diseases. If the soil becomes too acidic due to an overabundance of coffee grounds, it may disrupt the balance of beneficial microorganisms, further increasing the risk of fungal issues. 

You also need to be aware that the slow decomposition rate of coffee grounds can contribute to the problem. As grounds break down, they can create pockets of organic matter where fungal spores can thrive, exacerbating the risk of fungal diseases in the soil.

To mitigate these potential issues, it's important to use coffee grounds in moderation, ensure they are properly mixed into the soil, and monitor soil acidity and moisture levels to prevent the development of fungal diseases.

Ideal Soil PH for tomatoes

Tomatoes kinda like their soil a bit on the sour side, you know? Not too acidic, but just a tad. Think somewhere between 6.0 and 7.0 pH level, which is slightly acidic to neutral. 

Many gardeners assume coffee grounds dramatically acidify soil, but spent coffee grounds are often much closer to neutral than expected. While repeated heavy applications can still affect soil conditions, coffee grounds are generally not considered a reliable way to lower soil pH.

Excessive acidity can also create conditions favorable for certain fungal diseases. If the soil becomes too acidic due to an overabundance of coffee grounds, it may disrupt the balance of beneficial microorganisms, further increasing the risk of fungal issues. 

They can handle a bit of acidity or a touch of alkaline soil, but they really thrive when the soil is just right. Adding too much coffee grounds can throw off the pH and create issues for the tomatoes, companion plants and soil microbiome.

Signs tomatoes are benefiting from added coffee grounds

If your tomato plants are loving the coffee grounds, you'll likely see some positive signs! Clues include healthier-looking leaves, vibrant green color, and robust growth.

On the other hand, if they're not so keen on the use of coffee grounds, you might notice signs of nutrient deficiencies, such as yellowing leaves or stunted growth.

Keep an eye on your plants and adjust your coffee grounds usage accordingly to keep them happy and thriving!

How to add coffee grounds to the garden

1.  Collect Coffee Grounds: Start by collecting used coffee grounds from your coffee maker or local coffee shops. Make sure to use organic, unflavored coffee grounds for best results.
2. Allow Coffee Grounds to Cool: Allow the grounds to cool down to room temperature before using them in your garden.
3. Prepare the Tomato Plant: Choose a mature tomato plant that is already established in your garden. Avoid applying coffee grounds to newly planted or young seedlings. They may be more sensitive to changes in soil composition.
4. Apply Coffee Grounds: 
   • Sprinkle Method: Simply sprinkle the coffee grounds around the base of the tomato plant, making sure to spread them evenly in a thin layer.
   • Mix into Soil: Alternatively, you can mix the coffee grounds directly into the soil around the tomato plant. Use a garden trowel or rake to gently incorporate the coffee grounds into the top few inches of soil.
5. Avoid Excessive Application: Remember to use coffee grounds in moderation. While they can be beneficial for tomato plants, applying too much at once can lead to issues with soil pH and nutrient imbalances. A thin layer of coffee grounds spread around the base of the plant is typically sufficient.
6. Monitor Plant Health: Keep an eye on your tomato plants after applying coffee grounds. Look for signs of nutrient deficiencies or excess acidity, such as yellowing leaves or stunted growth. If you notice any problems, adjust your application of coffee grounds accordingly.

Other kitchen scraps that can be used in the garden?

While coffee grounds can be useful, they're just one of many compostable kitchen scraps. Banana peels, eggshells, vegetable scraps, and other compost materials can all contribute to healthy soil when added to a well-managed compost pile.

What are other kitchen leftovers that can be used in the garden?

1. Banana Peels:
   • Benefits: Banana peels are rich in potassium, which is essential for plant growth and flowering. They also contain small amounts of other nutrients like phosphorus and magnesium.
   • How to Use: Chop or tear banana peels into small pieces and bury them in the soil near plants or add them to your compost bin. They will decompose over time, releasing nutrients into the soil.
2. Egg shells:
   • Benefits: Eggshells are a good source of calcium, which helps prevent blossom end rot in tomatoes and other fruits. They also contain trace amounts of other minerals like magnesium and phosphorus.
   • How to Use: Crush eggshells into small pieces and sprinkle them around the base of plants or incorporate them into the soil. You can also add them to your compost bin to enrich the compost with calcium.
3. Vegetable Scraps:
   • Benefits: Vegetable scraps like carrot tops, potato peels, and lettuce leaves can be added to compost bins to create a healthy compost pile for the garden.
   • How to Use: Chop vegetable scraps into smaller pieces and add them to your compost bin along with other organic materials.
4. Citrus Peels:
   • Benefits: Citrus peels contain natural oils that can repel pests like ants and aphids. They also break down slowly, adding organic matter to the soil.
   • How to Use: Place citrus peels around the base of plants or bury them in the soil to deter pests. Avoid using large quantities, as citrus peels can be acidic and may harm certain plants.

My favorite amendments for tomatoes

1. Epsom Salts:
   • What They Do: Epsom salts provide magnesium and sulfur, which are important for making plants healthy and green.
   • How They Help Tomatoes: They prevent yellow leaves and help tomatoes grow strong and make lots of fruit.
   • How to Use: Mix epsom salts with water and pour around tomato plants or mix into the soil.
2. Blood Meal:
   • What It Is: Blood meal gives plants extra nitrogen, which helps them grow big and green.
   • How It Helps Tomatoes: It makes tomatoes grow lots of leaves and strong stems.
   • How to Use: Sprinkle blood meal around tomato plants or mix it into the soil.
3. Bone Meal:
   • What It Is: Bone meal has phosphorus, which helps plants grow roots and make flowers and fruit.
   • How It Helps Tomatoes: It makes tomato roots grow strong and helps them make lots of flowers and fruit.
   • How to Use: Mix bone meal into the soil before planting or sprinkle around tomato plants.

Making Compost for Tomatoes

Building compost for tomatoes is a fantastic way to enrich the soil and provide essential nutrients for healthy growth. One approach is to gather organic material from your kitchen and yard. I like to use vegetable scraps, coffee filters, grass clippings, and even paper coffee filters.

Layer these materials in a compost bin or pile. Make sure to add a small amount of each component to maintain a balanced mix. To supercharge your compost, consider adding used tea bags! Tea bags are rich in organic matter and can break down quickly to create nutrient-rich compost.

Adding old coffee grounds into your compost pile is a great way to introduce key nutrients and promote the growth of beneficial microbes. Over time, the compost will decompose into a nutrient-rich mixture that can be used to feed your tomato plants.

Remember to turn the compost pile regularly to aerate it and speed up the decomposition process.

Read my post Cheap Ways to Add Nitrogen to the Soil if you want to learn more!

The picture below is from last fall. We were about to have a hard freeze, so I picked every tomato from the raised bed and let them ripen slowly indoors.

Frequently Asked Questions

MORE GARDENING POSTS YOU'LL LOVE

Once you've found yourself bitten by the garden bug, you'll find yourself wanting to know everything! Check out my post How to Grow Tomatoes, Guide for Growing Potatoes or How to Save Sunflower Seeds. And don't forget about Composting Egg cartons!

Happy gardening!

Meg