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Are Coffee Grounds Good for Tomato Plants?

Gardeners worldwide recommend coffee grounds for a wide range of gardening applications. From pest control to mulch and fertilizing, there are numerous ways you can utilize them. But are these claims backed by science? Well, there are tons of gardening myths out there regarding coffee grounds.

coffee grounds for tomato plants

While coffee grounds are proven to be beneficial for many kinds of plants, are coffee grounds good for tomato plants? Let us find out whether using coffee grounds in your tomato garden can help tomato plants or harm them.


Should You Use Coffee Grounds to Fertilize Tomato Plants?

One of the most popular ideas is to use coffee grounds as fertilizer for tomatoes. The argument behind this claim is that coffee grounds contain nitrogen, potassium, and phosphorous, which are essential macronutrients for optimal growth of tomatoes.

Although this can work in theory, it is not very practical. Essentially, coffee grounds get broken down to release nutrients into the soil. However, they do not provide immediate nutrients to the soil. They only increase the nutrient content of the soil over time.

Unfortunately, their nutrient content is very minimal to offer any significant benefit to tomatoes. For instance, coffee grounds only contain about 2% nitrogen. Even an average slow-release fertilizer for tomatoes contains higher concentrations of nitrogen, potassium, and phosphorous. During the early growth stages of tomatoes, a lot more nitrogen is required to boost foliage growth.

Besides, tomatoes grow very fast and are nutrient hungry. Thus, invest in better organic fertilizers that are recommended for tomatoes to help them thrive at every growth stage.


Can You Apply Coffee Grounds as Mulch for Tomatoes?

Mulch is an important material for gardening. It is beneficial in many ways when used around tomato plants. It offers protection against too much heat, prevents the likelihood of water splash back, discourages weeds, and helps the soil retain moisture.

However, are coffee grounds good for tomato plants when used as mulch? While materials such as grass clippings, straw, crushed leaves, and wood chips are good for mulch on tomatoes, coffee grounds are not recommended.

Using coffee grounds as mulch on tomatoes can cause more harm than good. One of the issues is water. When coffee grounds sit, they compact to form a hard layer of mulch over the soil.

Unfortunately, this hard layer can result in a hydrophobic surface. Rather than assisting the soil retain water, the hard layer of ground coffee prevents water from reaching the soil. Consequently, the roots of tomato plants will fail to get sufficient water supply. Also, a very thick layer of coffee grounds can lead to aeration problems in the soil, thereby suffocating the roots.


Do Coffee Grounds Acidify the Soil?

Another purported application of coffee grounds on tomatoes is to acidify the soil. Tomatoes grow best in slightly acidic soil, with a pH level of about 6 to 6.5. You can use soil test strips or a pH meter to test your soil for its pH level. In case the soil has a very high alkaline level, you should add a soil acidifier.

Although coffee is naturally acidic and thought to boost soil acidity, it has insufficient acidity to help tomatoes. Coffee grounds have a neutral pH level of 6.5 to 6.8. Also, used coffee grounds have lower acidity as much of it is already extracted during brewing.


Will Coffee Grounds Act as a Weed Barrier Around Tomatoes?

Keeping the garden free of weeds is quite challenging. Sometimes, planting certain herbs and flowers alongside tomato plants helps to prevent weeds. For instance, basil, chives, nasturtiums, and marigolds work as weed barriers when planted around tomatoes. Also, they help control pests.

Although coffee grounds are known to help in keeping weeds away from the garden, they are not effective weed barriers for tomatoes. They block air and water from the soil to prevent weeds, but tomatoes need a lot of water and air in the soil to thrive. Thus, coffee grounds can kill tomatoes when used as a weed barrier.


Do Coffee Grounds Deter Tomato Pests?

A research study conducted by the University of Nebraska in 2002 tried to find out whether caffeine has any effectiveness in repelling slugs and snails. The research found that concentrated levels of caffeine are lethal to pests. Since coffee grounds have caffeine, the research findings are extrapolated to mean that it can have a similar effect.

However, used coffee grounds have minimal caffeine levels. Most of their caffeine is already extracted into your favorite cup of Joe. Thus, used coffee grounds will not deter pests such as snails and slugs. They will roll over them and find their way to your juicy tomatoes.

Also, there is no evidence that coffee grounds can deter other pests that like tomatoes such as flea beetles, white flies, or aphids. If you want to eradicate a pest infestation or deter pests, try other remedies that are specially made to deter particular pests. Also, try companion planting of tomatoes as a natural pest deterrent method.


Are Coffee Grounds Effective When Used as Compost for Tomato Plants?

Another claim about coffee grounds is about using them as compost for tomatoes. Essentially, a healthy compost requires a proper ratio of carbon and nitrogen to break down easily and offer tomato plants the nutrients they require. Fortunately, coffee grounds offer a reliable material to make compost for tomatoes.

Mixing about 20 percent of coffee grounds into your compost pile is beneficial for tomatoes. However, exceeding this percentage may inhibit decomposition.



So are coffee grounds good for tomatoes? Rather than throwing away coffee grounds after brewing coffee or when they become stale, use them to make a compost pile for your tomato plants. Coffee grounds are proven to help tomatoes thrive when used as compost. Using coffee grounds as mulch, weed control, or fertilizer for tomatoes will do more harm than good. Thus, only use coffee grounds in the recommended way to avoid harming your tomatoes.


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