Tomato Week

Are Coffee Grounds Good for Tomato Plants? Err, Probably Not!

Should you put coffee grounds in your tomato garden? It’s commonly discussed online and in gardening groups, so you’re not alone if you’ve been asking yourself this.

Many people think that because coffee is acidic, it will be good for their tomatoes because tomatoes prefer slightly acidic soil. Coffee grounds also contain nitrogen, which most plants need to grow. Are coffee grounds good for your tomato plants?

It makes a lot of sense in theory, but in reality, the coffee-grounds-in-the-garden situation is more complex. Coffee grounds probably won’t harm your tomato plants, but they have limited use cases when it comes to improving the health of your tomato plants.

Gardening myths can be pervasive. Just check out YouTube or your local gardening Facebook group – they’ll be full of myths. From eggshells to Epsom salt to baking soda, the gardening world is full of supposed miracle cures and garden “hacks”.

In the post, we’ll investigate how gardeners are told to use coffee grounds in their gardens. We’ll cover whether there’s any evidence to support these common gardening practices using coffee grounds. Then, in the interest of providing you with a concise answer, I’ll give a TL;DR on how I recommend using coffee grounds with your tomato plants and in the rest of your garden.

Common ways to use coffee grounds in the garden

Common ways to use coffee grounds in the garden

Before we get into the ways I recommend using coffee grounds on your tomato plants, let’s talk about the ways you might have already heard about. Here are some of the most common ways to use coffee grounds in the garden and my take on whether or not they’re worth your effort.


nitrogen content in the soil

Coffee grounds are often touted as a way to improve the nitrogen content in your soil. This is because coffee grounds contain 2% nitrogen, and nitrogen is essential for plant growth.

The jury is still out on how effective coffee grounds are at improving the nitrogen content of your soil. Some studies have shown that coffee grounds can help increase your soil’s nitrogen levels, while other studies have found no significant effect.

If you’re looking for a way to improve the nitrogen content of your soil, I recommend using compost or manure instead of coffee grounds. These organic matter options are more effective at improving the nitrogen levels in your soil and are also a great way to improve the overall health of your soil.


Using coffee grounds as a nitrogen fertiliser for tomato plants

Using coffee grounds as a nitrogen fertilizer for tomato plants

Using coffee grounds in your compost can add nutrients to the soil over time, but coffee grounds are ineffective as a fertiliser. Try a tomato and vegetable fertiliser or an organic fish emulsion fertilizer to fertilize your tomato plants. Both will have the nitrogen and other elements your tomato plants need to thrive.


Composting coffee grounds

Composting coffee grounds

Using coffee grounds as a mulch

Coffee grounds tend to compact and form clumps, preventing air and water from reaching plant roots. Plus, you’d need a nearly unfathomable amount of grounds to use as a moisture-retaining mulch in the garden. So what’s a good alternative for mulch?

Chopped leaves or grass clippings are great options that offer similar benefits without any negative side effects. So go ahead and enjoy that cup of joe – just stick to composting those used grounds instead of using them as mulch.


Acidifying the soil

It makes sense that many gardeners believe that adding coffee grounds to their soil is a good way to acidify it. Certain plants, like blueberries and hydrangeas, love acidic soil. Tomatoes do well with slightly acidic soil. So, does adding used coffee grounds to your soil acidify it?

The answer is: Maybe, depending on how much you use. Coffee grounds are usually close to neutral, around 6.5 to 6.8 pH, so they will not cause your soil to become acidic quickly. Most of the acid in coffee grounds is flushed out when the coffee is made. You’d have to add truckloads of coffee grounds to soil with a high pH in order to bring that number down by any significant amount.

If you do need more acidic soil, there are soil acidifiers that work quicker and with much smaller dosages. Coffee grounds are not an effective way to acidify the soil, so this is a gardening myth.


Improving soil structure

Improving soil structure

Coffee grounds can improve the structure of your soil, but there are much better amendments you could add. Still, they are one of many decent methods to improve the structure of your soil over time.

Coffee grounds help to break up compacted soils and improve drainage. They can also hold onto water and nutrients, making them available to plants for longer. However, coffee grounds alone will not make enough of a difference to justify using them.

If you want to improve your soil’s structure, try composting coffee grounds with other organic matter like leaves and grass clippings. You could also add composted manure or vermicompost (compost made with worms) to your garden beds.


Repelling pests in the garden

Repelling pests in the garden

Coffee grounds supposedly repel slugs and snails in the garden, but there isn’t scientific evidence to support that idea. Anecdotally, using coffee grounds to control pests is a popular strategy. Still, it’s difficult to find information about why, how, or if this works.

If you’re interested in trying this pest-repellent method for yourself, I suggest running some experiments and making note of your findings. This experiment set out to test whether slugs are repelled by coffee grounds and found that the slugs had no problem moving over the coffee grounds. For now, we can mark this use of coffee grounds in the garden as another myth.


Are coffee grounds good for tomato plants?

No. Coffee grounds do not provide significant benefits directly for tomato plants. The best way to use coffee grounds in your garden is to compost them and use that well-rotted compost throughout your gardens, including your tomato beds and containers.


Where to get coffee grounds for your garden?

So where can you find these valuable grounds? Many local coffee shops will happily give them away for free – all you have to do is ask. Just be sure to call ahead or check their website to see if they have a policy in place.

Some shops may require you to bring your own container to transport the grounds, while others may have biodegradable bags. And don’t forget about your friends and family – they might also be happy to save their grounds for you. Making coffee grounds a regular part of your gardening routine is easy with a little effort.

Here are some ideas when searching for local places that might agree to offload their spent coffee grounds:

  • Coffee shops and cafes;
  • Libraries;
  • Goodwill’s and other thrift stores that serve coffee;
  • Small, locally-owned restaurants;
  • Larger chain restaurants and stores;
  • Friends & family;
  • Neighbours. Ask in person or use apps like Next door, Facebook, and Craigslist to find people giving away coffee grounds.



FAQ about using coffee grounds on tomato plants

Do coffee grounds help tomato plants grow?

Coffee grounds are often touted as a great addition to soil for tomato plants. This is because coffee grounds are rich in nitrogen, which is essential for plant growth. However, there is no scientific evidence to support this claim. Coffee grounds don’t have enough nitrogen to be used as an effective fertiliser.

Can coffee grounds kill tomato plants?

Yes, coffee grounds can kill tomato plants if they are used in excess, but it’s unlikely unless you really pile them on. Coffee grounds can compact and form clumps, preventing air and water from reaching plant roots. If you’re looking to add nitrogen to your soil, there are better options than coffee grounds.

What is the best way to use coffee grounds on tomato plants?

Honestly, the best way to use coffee grounds in the garden is to compost them. Coffee grounds can also help improve soil structure, but that can be done by composting the grounds and spreading the compost throughout your garden.

In summary

There are a good many myths about gardening using coffee grounds, and I probably haven’t touched on half of them in this post. That being said, we covered some of the most common gardening myths dealing with coffee grounds and found that coffee grounds hold no secret cure or benefit for tomato plants.

Coffee grounds make a wonderful and relatively affordable addition to your homemade compost. It’s pretty easy to get your hands on a bulk amount of it so that you can become self-sufficient in composting, which is a huge milestone for any gardener. As far as being a nitrogen fertiliser, mulch, or pest repellent, coffee grounds don’t provide much bang for the buck and aren’t worth the effort. Look for other gardening methods to help you in these areas.

Now get out there into the garden and enjoy yourself! And be sure to share your experience with coffee grounds in the garden in the comment section. Sharing our collective experiences online means we can compile and discuss gardening information and experiments much easier than possible decades ago.

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