Rumors fly and the debate rages on. Are coffee grounds good for tomato plants? As modern-day gardeners, we often question gardening pearls-of-wisdom seen on the internet or handed down from previous generations. In this case, scientific studies have demonstrated whether or not tomatoes benefit from coffee grounds.
Fact or Fallacy: Do Tomatoes Like Coffee Grounds?
The short answer is yes and no. Like any garden additive, too much of a good thing can be detrimental. Consider what happens when too much fertilizer is applied to the lawn. Instead of a lush green carpet of grass, the turf turns brown.
So yes, tomatoes can benefit from coffee grounds, but only in moderation. Here are some positive ways coffee grounds improve soil quality and growing conditions for tomatoes:
- Adds nutrients – Coffee grounds contain nitrogen, phosphorus and potassium as well as micronutrients such as boron, calcium, copper, iron, magnesium and zinc.
- Slow release of nitrogen – The proteins in coffee grounds must first be broken down by microbes before nitrogen is available for plant absorption.
- Compatible pH – With an acidity measuring between 5.5 to 6.8, coffee grounds are within the ideal pH range for tomatoes.
- Compostable – With a carbon-to-nitrogen ratio of 20-24:1, coffee grounds can be added to compost. For optimal benefits, limit the coffee ground component to 20% of the total volume of organic materials.
- Fungal suppression – Studies have indicated the microorganisms which feed upon coffee grounds suppress common tomato diseases, including Fusarium, Pythium and Sclerotinia.
How To Use Coffee Grounds For Tomato Plants
With an estimated 700 million cups (165,611,766 L.) of coffee being consumed by Americans each day, keeping this by-product of the brewing business out of landfills is an earth-friendly option. In addition to home and work sources, coffee shops and restaurants may supply gardeners with used grounds for the asking.
Here are a few ways to use coffee grounds in the garden:
- Compost for tomatoes – When mixed with leaves or sawdust, compost made with coffee grounds provide essential nutrients for tomatoes while combating fungal diseases. Incorporate compost into the soil or use as mulch around tomato plants.
- Mulch – Spread a 1/2 inch (1.3 cm.) layer of fresh coffee grounds around tomato plants to retain moisture. Natural chemicals found in coffee grounds may suppress weed seed germination.
- Soil amendment – Planting tomatoes with coffee grounds encourages the growth of beneficial microorganisms. Earthworms consume the grounds and pull them deeper into the soil, which also improves soil structure.
- Coffee ground “tea” - Although, technically it would be coffee, this liquid fertilizer can be used to water tomato plants. Make the tea by adding two cups (473 mil.) of used coffee grounds to five gallons (18.9 L.) of water.
Again, moderation is the key when using coffee grounds on tomatoes. This java byproduct has phytotoxic qualities which can have an adverse effect on tomatoes when applied in excess.
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FAQs
Tomato Plants Like Slightly Acid Soil
How often should I put coffee grounds on my tomato plants? ›
How often can I put coffee grounds on my tomato plants? A sprinkling of coffee grounds mixed into the soil before planting tomatoes will not harm the plants. However, no additional coffee grounds should be added to the soil during the growing season.
Do you just sprinkle coffee grounds around plants? ›
Though gardeners most often use grounds that have been brewed, fresh coffee grounds can also be used. Only composted coffee grounds should be mixed into the soil, as fresh grounds will have a higher acid and caffeine content which may burn plant roots. Make sure that grounds aren't too wet to discourage possible mold.
Which vegetables do not like coffee grounds? ›
Coffee grounds inhibit the growth of some plants, including geranium, asparagus fern, Chinese mustard and Italian ryegrass. Conversely, grounds (used as mulch and compost) improve yields of soybeans and cabbage.
Can plants get too much coffee grounds? ›
Excess coffee grounds, if applied to the soil before composting, have multiple effects on the soil system. In addition to microorganisms tying up nitrogen temporarily, the caffeine residues in the spent coffee grounds can suppress germination and slow the growth of some plants.
How often can I water my plants with coffee grounds? ›
If you evenly sprinkle coffee grounds around the plants once a week or so, the amount will likely be okay.
Do you put coffee grounds on top of soil? ›
Adding coffee grounds directly to the soil as a fertiliser can be a good option. Coffee grounds are rich in nutrients, especially nitrogen. They also have some amount of other nutrients like potassium and phosphorous. Overall, this means that adding coffee grounds to your garden can work fairly well as a fertiliser.
What are the disadvantages of coffee grounds as fertilizer? ›
Coffee grounds are highly acidic, they note, so they should be reserved for acid-loving plants like azaleas and blueberries. And if your soil is already high in nitrogen, the extra boost from coffee grounds could stunt the growth of fruits and flowers.
Is it better to give coffee grounds to plants mixed with water or not? ›
The key to using used coffee grounds as a liquid fertilizer is dilution! Too much of a good thing is possible, particularly for plants potted in containers. We recommend using about a teaspoon of coffee grounds per gallon of water.
Why do tomatoes not like coffee grounds? ›
Nitrogen Drawdown
When coffee grounds are added directly to the soil, they begin to decompose. During this process, soil microorganisms consume nitrogen to break down the carbon-rich grounds. This phenomenon, known as 'nitrogen drawdown,' temporarily reduces the amount of nitrogen available to the tomato plants.
Some plants that benefit from coffee grounds include: acid-loving plants like azaleas, blueberries, and rhododendrons. plants that need nitrogen, such as tomatoes, peppers, and leafy greens.
What plants Cannot have coffee grounds? ›
Not all plants like coffee grounds because they are slightly acidic, contain caffeine and are nitrogen-rich. Some plants that won't thrive in these conditions include vegetables like Chinese mustard, grasses like Italian ryegrass, rosemary, lavender and flowering plants like geraniums.
Should I pour old coffee on plants? ›
It's okay to water plants with leftover coffee or to add coffee grounds to the compost pile but learning when and why to use coffee in the garden will protect your plants. Only use black, unflavored coffee with this method to offer plants a source of nitrogen which can fertilize certain indoor and outdoor plants.
Why put eggshells in your garden? ›
The shell of a chicken egg is comprised of about 96% calcium carbonate (CaCO3). Calcium is an essential plant nutrient and moderates soil acidity. Fast-growing plants deplete the soil of calcium very quickly so egg shells are an ideal supplement and feed for outdoor flowers, vegetables and fruit trees in your garden.
What plant benefits most from coffee grounds? ›
Acid-loving plants like azaleas, blueberries, and roses benefit greatly from coffee grounds, as they help to increase the acidity of the soil. Other plants such as tomatoes, carrots, and radishes also benefit from the slow-release nutrients in coffee grounds.
Do eggshells help tomato plants? ›
Most of us have heard that eggshells can help increase the calcium in our garden soil, and some of us may have even tried it in our own yards. The goal is to help prevent blossom end rot on tomatoes and other plants affected by calcium deficiency. As it turns out, using eggshells really doesn't fix anything.
Are banana peels good for tomato plants? ›
Banana peels are also brimming with potassium, which is excellent for plants like tomatoes, peppers or flowers. “Banana peels also contain calcium, which prevents blossom end rot in tomatoes,” the Cape Gazette adds.
How often do you feed coffee plants? ›
Caring for a coffee plant
Feed your coffee plant every two weeks during the growing season (March to September) with a liquid feed. Keep the compost moist but reduce watering during the winter when the plant is dormant. For more on house plant care: Caring for house plants.
