I have a lot of coffee grounds that I simply just add to my compost but a friend recently asked me whether coffee grounds can be added directly to the garden. While some plants can benefit from coffee grounds spread around their base, are coffee grounds good for tomato plants?
Coffee grounds can be like a tonic for your tomatoes but they should be used fairly sparingly and not relied on as a complete source of nutrients.
Before we discuss this in more detail, let’s have a look at the benefits of using coffee grounds around your garden.
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Benefits Of Coffee Grounds In The Garden
Essentially, coffee grounds are considered organic matter so you would imagine that they have some benefits when added to the garden. Here are just a few of them.
They Can Add Nutrients To The Soil
Coffee grounds are fairly high in nitrogen and as they break down, they will add this nutrient to the soil for the plants to take up through their roots. Coffee grounds also contain smaller traces of both potassium and phosphorus.
This means that coffee grounds can add the most essential nutrients for plant growth back into the soil. However, they shouldn’t be considered as a complete fertilizer but rather just a beneficial additive.
The nitrogen that is contained in coffee grounds gets released into the soil at a relatively slow rate as the microbes break down the proteins. This is particularly useful for fruiting plants such as tomatoes.
You don’t want to give your tomatoes too much nitrogen because this will promote lots of growth but reduce flowering and fruiting. That’s why tomatoes require a fertilizer that’s high in potassium if you want to harvest lots of those delicious fruits.
They Can Increase The Acidity Of The Soil
Coffee grounds are generally considered to be mildly acidic with a pH range from 6.5 to 6.8. However, this can vary depending on the types of beans that you’re using to make your coffee.
Tomato plants do prefer slightly acidic soil with a pH range between 6.2 and 6.5. Therefore, if your soil is not quite acidic enough for healthy tomato plants, coffee grounds may be of benefit.
However, if your soil is already quite acidic, I would not suggest using coffee grounds around your tomato plants. The increased acidity could prohibit the roots of the plants from extracting all the vital nutrients from the soil.
They Can Help Suppress Certain Fungal Diseases
Studies have been conducted that show that coffee grounds have antifungal properties which can be helpful to suppress the growth of fungal diseases. It was found that as the coffee grounds dissolved into the soil, they inhibited the germination of fungal spores.
This can be particularly useful for tomato plants that are susceptible to a number of fungal diseases. These primarily include Fusarium, Sclerotinia and Phytophthora.
This can be useful if you grow tomatoes in the same spot year after year. Although I recommend crop rotation and follow this practice myself, sometimes you don’t have a choice.
Therefore, adding some coffee grounds to the soil before planting your tomatoes, could be quite beneficial.
They Can Help The Soil Retain Moisture
Seasoned tomato growers will know that these plants are very thirsty and need adequate amounts of water to flourish. Adding organic material such as coffee grounds to the soil is a good thing because it can help with water retention.
This is particularly useful if you have sandy soil that drains too fast to sustain your tomato plants.
They Can Help To Improve The Health Of Your Soil
All the microbes and earthworms that live in your soil will happily feed on the used coffee grounds that you provide. This, in turn, improves the health of your soil and also improves the soil structure.
As the earthworms burrow through the soil, they create air pockets that are so essential for healthy plant growth.
Now that we understand some of the benefits of adding coffee grounds to the soil in our gardens, let’s discuss some of the disadvantages.
Disadvantages Of Adding Coffee Grinds To The Soil In Your Tomato Garden
While there are numerous benefits to using coffee grounds in the garden, you should also be aware of some of the risks involved. Here are just a few to consider.
The Caffeine In Used Coffee Grounds Can Inhibit Growth
The amount of caffeine that remains in the used coffee grounds will be determined by the variety of beans that you’re using and the brewing technique.
If there are high levels of caffeine in the grounds, this can inhibit the growth of your tomato plants.
This is especially true when the plants are still young and haven’t yet developed a sturdy root system.
Some Coffee Grounds Can Contain Chemicals
It is possible for low-quality coffee bean varieties to contain some chemicals that were added during production or roasting.
While these may not be in toxic amounts, if you’re practising sustainable gardening, you do want to refrain from adding chemicals to your soil.
Coffee Grounds Can Compact When Added On Top Of The Soil
If you just dump the coffee grounds on top of the soil around your plants, they can compact and stop both air and water from getting through into the soil.
This is usually a problem if the grounds are very fine. They can potentially fill the air pockets in the soil and suffocate the roots of your plants.
How To Use Coffee Grounds Safely Around Your Tomato Plants For The Best Results
As you can see, there are plenty of benefits to using coffee grounds around your tomato plants but also some drawbacks. Here are my suggestions for the best way to use coffee grounds safely in your garden and around your plants.
Add Them To Your Compost Pile
When you add coffee grounds to your compost bin or pile you can reap all of the benefits and none of the disadvantages. Just remember to have a good mix of green and brown waste to ensure that your resultant compost is highly nutritious.
This is primarily the way that I use coffee grounds in my garden. I have a kitchen compost bucket that I empty the grinds into on a daily basis. To this, I also add all of my organic kitchen scraps.
Then, once a week or so, I take this bucket out to one of my compost bins and deposit the entire contents into it. I also make sure that I add plenty of brown materials such as dried leaves to add plenty of carbon into the compost materials.
Before planting out my tomato plants, I collect some of the finished compost from the bins and spread this over the garden beds. I generally just rake this in lightly as I don’t want to disturb the soil and all the critters living in it too much.
This helps to get my tomato plants off to a good start by giving them the nutrients they need to grow a nice, strong root system.
Amend The pH Of The Soil
It’s a good idea to check the pH level of your soil before planting your tomato seedlings. If you find that the soil is too alkaline, you can add small amounts of coffee grounds to the soil but ensure that you work them in lightly.
You probably want to do this at least a couple of weeks before planting your tomatoes because it can take a little while for the coffee grounds to affect the pH level of the soil.
You’ll also find that adding compost to the soil will lower the pH as well. So, you might want to consider doing this instead.
Don’t Spread Coffee Grounds Around Tomato Seedlings
It’s important that you avoid adding coffee grounds around your tomato seedlings because the caffeine contained in the grounds will inhibit the growth of your plants.
It’s far better to amend your soil with compost a couple of weeks before planting.
Use A Small Amount Of Coffee Grounds To Protect Against Fungal Diseases
If you plan to grow your tomatoes in the same spot as last year, adding some coffee grounds to the soil may inhibit fungal disease growth.
You want to do this at least four or six weeks before planting your tomatoes to give the grounds enough time to break down into the soil.
Spread a thin layer (half an inch or 1.25 cm) of coffee grounds over the soil and water well. It might be beneficial to rake the grounds in lightly. This should stop them from forming a compacted layer on the surface.
Continue to water the soil to allow the coffee grounds to work their way down and encourage decomposition. Only plant your seedlings once there are no visible coffee grounds left on the surface of the soil.
To continue to protect your plants, you can add a very thin layer of coffee grounds around the base of your tomato plants. Make sure that your tomato plants are well-established before you do this.
Ensure that the coffee grounds aren’t too acidic. If you brew your coffee at a high temperature quickly, you’ll find that there is not a lot of acidity left in the used grounds.
Wait until the coffee grounds have fully decomposed into the soil before adding any more.
Frequently Asked Questions
Coffee grounds should make up a percentage of the green material that you add to your compost. Remember to also add plenty of brown, carbon-containing materials such as dried leaves and even paper and cardboard, to balance your compost.
When adding coffee grounds around your tomato plants, only apply them in a very thin layer. If the grounds are too thick, they’ll become compacted and won’t allow moisture through into the soil.
Acid-loving plants will benefit the most from coffee grounds. I’ve been known to spread a thin layer of coffee grounds around my hydrangeas to initiate a color change in the flowers.
Select an organic fertilizer that has high levels of potassium and phosphorus. You can also use a slow-release fertilizer that will release nutrients as your plants grow. You can either use a commercial fertilizer specifically formulated for tomatoes or use your compost. Just make sure that the carbon-to-nitrogen ratio is correct.
Coffee grounds can add nutrients and other benefits to your garden. But, they should be considered as a soil amendment rather than a complete fertilizer for your plants.
Your tomato plants may benefit from the acidity in the grounds and also their antifungal properties. This can help to avoid fungal infections in your tomato plants.
However, it is always best to add the coffee grounds to your compost. Then use this to feed your tomato plants. This allows the grounds to break down first. It also avoids the possibility of the caffeine stunting the growth of your plants.
For this reason, coffee grounds should not be added directly to the garden soil around young plants. This will have a negative effect on the growth of your plants.
However, you can use them a month or so before planting to amend the pH and limit any fungal spores from germinating.
It’s also a good idea to always check the pH and the nutrient content of your soil before planting a new vegetable garden. This will tell you what you might need to add before planting.
For some more useful information on the use of coffee grounds in your garden, you might want to check out these articles: