Should You Use Coffee Grounds For Tomato Plants? (What Research Says)

Quick Answer: Should You Use Coffee Grounds For Tomato Plants?

Coffee grounds are touted for benefiting tomato plants. It is claimed to fertilize the soil, work as mulch, deter garden pests, prevent fungal infections, and lower the pH of soil. Most of these claims are not supported by science. But, the coffee grounds work best when added to the compost pile. The compost may help in fertilizing tomato plants.

This article attempts to answer whether you should use coffee grounds for tomato plants.

I have compiled my personal experience, research articles, and insights of fellow gardeners to answer the question.

Keep reading further to know more!

Using Coffee Grounds For Tomato Plants – Is it Good?

The coffee grounds are rich in nitrogen-rich proteins that are required for seed germination.

Many gardeners claim that used coffee grounds are good for acid-loving plants, including tomatoes. However, some argue that tomatoes don’t respond well to coffee grounds.

Some of these claims are backed by supporting articles, while others do not. Let us find more about what is the reality of using coffee grounds in your tomato garden.

Coffee Grounds In Compost Pile

The coffee grounds may work as an excellent addition to a compost pile. But, do not use more than 20% of coffee grounds in the compost pile.

It can be added as an organic matter for tomato plants.

The research studies suggest that coffee grounds can be added to the compost pile.

They provide bacteria nitrogen, which helps in converting organic matter into compost. The uncomposted coffee grounds are not an effective nitrogen fertilizer.

The experts do not recommend using more than 20% of coffee grounds in your compost pile.

I add composted coffee grounds to the hole, where tomato seedlings are about to be planted. It will provide slow-release nutrients to the tomato plants and improve soil composition.

For container-grown tomatoes, you may mix coffee grounds and soil in a 1:1 ratio. The University of Florida suggests mixing the soil with coffee grounds at least twice a year.

So, I would recommend adding coffee grounds to the compost pile and using it for tomato plants.

Benefits of Adding Coffee Grounds to Tomato plants

Here are some of the reasons you should add them –

1. Coffee Grounds Give Nitrogen Boost To Tomatoes

The coffee grounds may not work as a replacement for nitrogen fertilizers to initiate the growth of tomato plants.

Instead, they may release the nutrients into the soil as they decompose, which helps the tomato plants.

Coffee grounds contain nitrogen, potassium, magnesium, copper, and other trace minerals. They have a carbon-to-nitrogen ratio of 20:1.

Many blogs advise sprinkling coffee grounds around the tomato plants as a nitrogen fertilizer. But these nutrients will be available to the tomato plants only as the grounds decompose.

A germination test at the GrassRoots Garden in Eugene showed that coffee grounds are not a nitrogen fertilizer.

Instead, they cause poor rates of germination and stunted growth. It may be because the coffee grounds support the growth of soil-borne organisms that use nitrogen. So, the nutrients may not be available for tomato plants.

If you want to add coffee grounds around tomato plants, add nitrogen fertilizer as well. The additional nitrogen in the fertilizer may be used by your tomato plants.

2. Coffee Grounds As A Mulch

The thin layer of coffee grounds may be sprinkled around tomato plants and then topped with organic mulch. It helps to save moisture and prevent weeds.

Many gardeners use a thin layer of coffee grounds as mulch to protect their tomatoes plants. It is proposed to save moisture and prevent weeds.

In reality, the thick layer of coffee grounds may prevent the moisture and air from going to the soil. The roots may thus be devoid of oxygen.

Some studies have shown that using coffee grounds as mulch cause reduced seed germination and plant growth. It happens in areas where you are growing plants from seed.

The coffee grounds may still work as mulch but in small amounts. You may apply ½ inch of used coffee grounds and top it with 2-3 inches of organic mulch around the base of the tomato plants.

This thin layer of coffee grounds may give a boost of nitrogen to tomato plants.

3. Coffee Grounds To Deter Slugs And Snails

Research has shown that 1-2% caffeine may deter snails and slugs.

But, coffee grounds do not have a sufficient amount of caffeine to repel snails and slugs.

Slugs and snails are a common problem in my tomato gardens. Coffee grounds have been suggested to keep snails and slugs in check.

New research has discovered that slugs and snails hate caffeine. About 1-2% of caffeine solution killed the snails and slugs in two days.

In contrast, there is no published evidence that coffee grounds deter snails and slugs.

It may be because coffee grounds have a minimal amount of caffeine and may not be sufficient to kill these pests.

Also, I couldn’t find any scientific research supporting the ability of coffee grounds to attract pests or earthworms.

4. Coffee Grounds To Lower pH Of The Soil

Many gardeners claim that coffee grounds are acidic and may support acidic tomato plants. But, the studies have shown that the composting coffee grounds have variable pH.

Tomato plants grow well in acidic pH. Some gardeners claim that coffee grounds may lower the pH of the soil and make it acidic. So, they may support the growth of tomato plants.

But, it may be true only with unwashed coffee grounds. The acid in coffee is water-soluble, and so they are most likely in brewed coffee.

Also, studies on coffee ground composting have shown a variable pH range (mildly acidic to alkaline). The pH changes will occur only in the vicinity of coffee grounds and not the entire soil.

So, the coffee grounds won’t make a good acidic compost as their pH levels will change over time.

5. Coffee Grounds To Manage Weeds

The sprinkling of coffee grounds around the tomato plants may help to prevent weeds. But, you may need a thick layer of coffee grounds as mulch. Future studies will determine if coffee grounds manage weeds.

The coffee grounds are suggested to manage weeds short duration and allow the garden to flourish. It was speculated that the toxic substances released from the decomposing coffee grounds may have an inhibitory effect on weeds.

The coffee grounds are used as mulch to control weeds. But, you may need a thick layer of mulch to suppress weeds effectively. This in turn may prevent the water from entering the soil as mentioned above.

The available research studies are unclear if coffee grounds help to control weeds. You may use the other weed controlling methods.

6. Coffee Grounds To Prevent Infections

Current research studies are inconclusive if the coffee grounds prevent or kill any fungal diseases affecting tomato plants.

Future studies will help to determine if composting coffee grounds are beneficial in treating fungal infections.

The tomato plants are sometimes affected by fungal disease, including Fusarium wilt and Verticillium wilt. It may be detrimental to the plants.

The coffee grounds have non-pathogenic organisms, including Pseudomonas, Fusarium, Trichoderma, and pin molds. It may prevent the pathogenic fungi from affecting the tomato plants.

A study has demonstrated the non-pathogenic organisms found in the decomposing coffee grounds suppressed the fusarium crown and root rots of tomato plants.

But their efficacy in gardens has still not been tested.

Another study showed that caffeine may suppress the growth and development of certain pathogens. But, it requires a higher concentration of caffeine than found in coffee grounds.

I find that the available studies are inconclusive whether coffee grounds kill fungal pathogens and prevent diseases. More studies are required to draw some conclusions.

How to use coffee grounds for tomato plants?

You may use up to 20% by volume of coffee grounds in the compost pile and then add to the tomato plants. Also, the thin layer of coffee grounds may work as mulch.

Many gardeners use coffee grounds for tomato plants to benefit them both economically and environmentally.

My best recommendation is to add coffee grounds to the compost mixture and then using for tomato plants.

Also, I would not recommend using more than 20% by volume of coffee grounds in the compost pile.

It is preferable to cool the coffee grounds before adding them to the compost pile so that the beneficial microbes are not killed.

They may also work as a thin layer of mulch. But do not lay them heavily as they may block air and water exchange.

However, more science-based studies are required to support other speculations and draw any conclusions.

Here is the video on how to fertilize tomato plants with coffee grounds:

FAQs

What will happen if you pile up coffee grounds in your tomato garden?

The piling up of coffee grounds may be detrimental to the tomato plants. The small particles of the coffee grounds may lock together, thus creating a water-resistant barrier in the garden. It may block the water from entering the tomato plants and affect their growth.

Can fresh coffee grounds be added to the garden soil of tomato plants?

The fresh coffee grounds may be phytotoxic to certain plants. It will interfere with plant growth. It is recommended never to let the roots or stems of the plants come in contact with fresh coffee grounds.

What happens if coffee grounds are sent to the landfill?

If the spent coffee grounds are sent to the landfill, they emit methane, a greenhouse gas. It is estimated to be 28 times more potent than carbon-di-oxide. But, they may be upcycled into different products to prevent emissions.

Summary

I hope this article has helped you to decide if you can use coffee grounds for tomato plants.

If you have had any success with using coffee grounds for tomato plants, I would be interested to know your experience and suggestions.

Do share the article with your friends and family! Happy gardening!

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