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Are Coffee Grounds Good For Tomato Plants

If you are growing tomato plants, you might be wondering whether coffee grounds are good for them. A lot of people put coffee grounds around their plants to help them grow, but is this something that will make your tomato plants happier, or should you avoid it?

Coffee grounds do have some benefits for tomatoes, but they need to be used in moderation. Coffee grounds are thought to be good for coffee because they contain some great nutrients, and they are often acidic, which tomatoes like. However, in large quantities, they can strip nitrogen out of the soil.

Published: October 17, 2022.

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In this article, we’re going to explore the value of coffee grounds and whether you should use them on your tomato plants or not. This will help you to determine what to do with your old coffee grounds and how to keep your tomatoes happy.

Why Are Coffee Grounds Good For Tomatoes?

There are several things that make coffee grounds good for your tomato plants. Understanding the benefits is valuable because this will make it easier to weigh these up against the drawbacks and thoroughly assess whether this is a good thing to do.

Before we explore the benefits, it’s worth noting that so far, few studies have explored the value of coffee grounds for tomato plants. Some, therefore, debate the benefits, and some people say that you shouldn’t put coffee grounds on plants at all.

You may wish to run some tests of your own, comparing tomato plants with and without coffee grounds.

That said, there are some reasons that tomatoes should benefit from the spent coffee, so let’s look at those.

Benefit 1: Nutrient Rich

One of the first big advantages of using coffee grounds is that they contain lots of nutrients. Tomatoes are heavy feeders and benefit from being planted in very rich soil, so the additional nutrients coming from the coffee grounds will be welcomed by them.

Coffee grounds contain things like zinc, calcium, iron, and copper, which are important micronutrients. They also contain the macronutrients potassium, phosphorus, and nitrogen, making them great for tomatoes.

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Benefit 2: Somewhat Acidic

Secondly, their pH value is generally compatible. Coffee grounds can vary depending on where you buy them from, but most are slightly acidic, with a pH value below 7.0 but above 5.5. This means they are usually within a suitable range for adding to your tomato plant’s soil, and they will lightly acidify it.

Tomato plants like soil that is between 6.0 and 6.8, making coffee grounds a suitable addition to the soil. Remember that they will only slightly modify the pH value, so even if you add quite acidic coffee grounds, it’s unlikely that they will make the soil too acidic for the tomatoes to thrive.

Most vegetables grow better in slightly acidic soil, and coffee grounds may be able to help provide this.

Benefit 3: Antimicrobial

Another advantage is that coffee grounds are thought to be antifungal and antimicrobial. That means they will stop unwanted organisms from growing in your tomato plant’s container and infecting your plant.

They may protect your plant from being attacked by all kinds of unpleasant microorganisms in the soil, keeping it healthy and allowing it to produce more fruit. If you struggle with mold or fungal infections on your plants or in your soil, the coffee grounds should help.

They may not be able to tackle infections on the foliage, but they will create a more sterile environment that should be significantly better for the tomatoes overall.

Studies have also shown that the microorganisms that feed on coffee grounds are beneficial and can even suppress common diseases.

For example, Sclerotinia, Fusarium, and Pythium may all be suppressed by the microbes that frequently feed on coffee grounds, reducing the risk of your tomato suffering from any of these diseases.

Benefit 4: They Will Break Down

Once you’ve added the coffee grounds to your tomato’s pot, they will start breaking down and enriching the soil.

Their nutrients will become available to the plant, and they will disappear. This means you don’t need to do anything further yourself. They are a fully compostable additive that will provide nutrients and break down into more soil.

Benefit 5: They Are Natural

Some gardeners don’t like using commercial feeds and fertilizers on crops that they are going to consume because they don’t know what’s in them.

Coffee grounds, however, are safe for human consumption and a lot of people drink coffee. That might make you feel more comfortable about adding the grounds to your garden.

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Why Aren’t Coffee Grounds Always A Good Idea?

That all sounds very promising and may leave you eager to start adding piles of spent coffee to your tomatoes’ containers immediately.

However, you should be cautious because there are a few downsides to coffee grounds, too. Used in moderation, they may be fine, but there are some drawbacks to consider.

Drawback 1: The Nutrient Boost Is Slow

A lot of people talk about using coffee grounds as a sort of instant fertilizer for plants, but they don’t work this way. Coffee grounds do contain nutrients, but these nutrients are locked inside the grounds, and until they break down, they won’t become accessible to the plant.

That means that adding coffee grounds isn’t the immediate boost that many people think it is. The coffee grounds will release those nutrients gradually, but they aren’t going to feed a young plant all it needs from day 1.

Drawback 2: The Nutrients Aren’t Super High

Although coffee grounds do contain plenty of nutrients, they aren’t as rich as many sources claim. They have about 2 percent nitrogen, while many commercial fertilizers have much, much higher percentages. The other macronutrients and micronutrients will vary.

That means you can’t replace your ordinary fertilizer with coffee grounds and still expect healthy, vigorous plants. You will need to keep feeding your tomatoes, and the coffee grounds will make a small degree of difference. Although they do provide nutrients, the quantities are limited.

Don’t use coffee grounds if your tomatoes are showing signs of nutrient deficiencies. They will not be enough to help, and your plant will continue to struggle.

Drawback 3: They Won’t Reliably Change The pH Value

If you’re adding coffee grounds to acidify the soil, you should be a little bit cautious. Coffee grounds might do a great job of acidifying in some cases, but they aren’t reliable. Some coffee grounds are much more alkaline than others, and this could have the opposite effect on the soil, potentially damaging your tomato plant.

You should check the pH of the grounds before using them, but be aware that even if they are acidic, they may not serve many purposes. It has not yet been proven that adding them to the soil consistently lowers the pH level.

It is also worth noting that your plant may not need the pH lowering. Tomatoes like acidic soil, but not very acidic. The grounds may, therefore, not be helpful.

Drawback 4: They May Temporarily Reduce The Nitrogen Levels

Although coffee grounds contain nitrogen, adding them to your plant’s pot could temporarily reduce the amount of nitrogen available to the plant. That might sound surprising, but it is certainly true.

When organic matter decomposes, the microbes that are breaking it down absorb nitrogen from the surrounding soil as part of the decomposition process.

They will take up all the available nitrogen and use it while breaking the coffee grounds down – and this will lead to a deficit in nitrogen while the grounds are decomposing.

When the coffee grounds are broken up, the nitrogen they contain will be released into the soil, along with the nitrogen borrowed for the decomposition process. However, it can take quite a while for this to happen, and in the meantime, your tomatoes will struggle to get the nitrogen they need in order to grow properly.

Should You Use Coffee Grounds On Tomato Plants?

So, overall, are coffee grounds good for tomato plants? The answer is that they probably have some benefits, but further study is needed to understand whether these outweigh the drawbacks.

It seems that coffee grounds do help the plants out in some ways, but they can also hinder their growth and could lead to nutrient deficiencies.

What Should You Do With Coffee Grounds Instead?

If you’ve got a lot of coffee grounds you want to use up, the best thing to do is usually compost them. This will allow the nutrients to be unlocked and released, ready for the plants to use, but it won’t involve taking nitrogen from your tomatoes in the meantime.

Coffee grounds are thought to be very good for your compost, so this is a great, eco-friendly way to dispose of them.


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Few Final Words

Although many people say coffee grounds are good for tomatoes, there is limited evidence of this so far.

It is certain that they could have some drawbacks, so you should be wary of adding them to your tomatoes, although, in small quantities, they are unlikely to do any harm.



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