Coffee grounds are recommended by amateur gardeners worldwide for a variety of gardening problems . From fertilizing to mulching to pest control, there seems to be nothing a spoonful of used coffee grounds can’t do. But can you fertilize tomatoes with coffee grounds? We’ll explain how to use this home remedy so it won’t harm your tomato plants either.
How does coffee grounds help tomato plants?
Coffee grounds provide good amounts of essential nutrients, all needed for healthy growth, and should still benefit tomatoes by:
- increasing the nutrient content
- balances the pH
- stabilizes soil temperature
- increasing water retention
- reducing harmful bacteria and fungi
- improves germination
- increases the growth rate
- promotes earthworm activity
- serves as a natural and organic insecticide
- reduces weeds
The main nutrients to add to the soil with coffee grounds are:
Since nitrogen and phosphorus are two of the three main nutrients for plants (the other being potassium), coffee grounds are a great way to fertilize your tomato plants. While nitrogen levels can vary, it is often the most valuable nutrient in coffee grounds.
There is also evidence that coffee grounds are good for earthworms and compost worms, which in turn helps improve the soil.
In addition, research suggests that the natural bacteria and fungi found on decomposing coffee grounds reduce harmful fungi and even prevent them from becoming established in the soil of tomato plants.
Finally, coffee grounds can also be used as a natural insecticide . The reason for this is the caffeine it contains. Usually insecticides have harmful effects because they also kill beneficial worms and pollinating insects, but coffee grounds are a much safer and natural alternative. For example, there is some evidence that coffee grounds repel insects such as ants, slugs and slugs .
However, there is still debate about the science on this topic, as some believe that the caffeine is gone after coffee is brewed and others say that much still remains in the coffee grounds.
Do coffee grounds make the soil acidic?
Tomatoes are an acidic food, so it’s no surprise they like a slightly acidic soil. Tomato plants prefer a soil pH between 6.0 and 6.8, while a neutral pH is measured at 7.0.
Science is divided on whether coffee grounds make the soil acidic. In short, unused coffee grounds are acidic, but most of the acid is lost during brewing. This means that used coffee grounds have only a slightly acidic pH of 6.5-6.8. However, since this pH is right in the range of what tomato plants prefer, coffee grounds prove to be a great addition to the soil.
The pH of soils treated with coffee grounds increases for the first three weeks and then slowly decreases. For this reason, it is a good idea to check the pH of the soil every few months.
How to use coffee grounds as a tomato fertilizer
There are basically three ways to use used coffee grounds as a fertilizer or soil conditioner for your tomato plants:
- You can spread it directly on the soil
- mix it with mulch
- compost it first
Basically, you can add coffee grounds directly to the soil of your tomato plant. But coffee grounds can easily clump together if you use them in large quantities, preventing air and moisture from reaching the soil. That’s why it’s best to mix coffee grounds with mulch or compost them first. Leaves, bark and pine needles are good to use as mulch for tomato plants.
Spread a 1.5-inch-thick layer of used coffee grounds around the base of your tomato plants and cover with 5 to 8 inches of organic mulch.
Another way to fertilize tomatoes with coffee grounds is to spread 1 cup of used coffee grounds around the base of your tomato plant and work it into the top 5 to 8 inches of soil with a trowel or small cultivator. This will stimulate decomposition of the coffee grounds and prevent soil compaction problems.
If you compost the coffee grounds first, you can add them to the compost pile in the fall so they are ready for use in the spring. When doing this, you should pay attention to three things:
- Coffee grounds should make up no more than 20% of the total compost.
- Wait 2-3 months for it to decompose before spreading it in your garden.
- Apply the already finished compost to the soil of your tomato plants in a layer of 2 to 5 cm.
Whichever method you choose, the important thing is: don’t let the coffee grounds (or compost) come into direct contact with the tomato plant. The same goes for mulch. You should leave at least a 2-inch space between the coffee grounds and the lower leaves. This is because coffee grounds and compost can cause mold, and their high nutrient content can chemically burn the plant.
How much coffee grounds should you use on your tomatoes?
While coffee grounds are great for the soil and compost, they can also be too much of a good thing. You should use coffee grounds in moderation. The high nitrogen and potential caffeine content can upset the soil or compost if used in excess.
Limit the amount of coffee grounds in your compost to no more than 20 percent. Coffee grounds are considered green material, such as fresh grass clippings and kitchen scraps, and must be mixed with brown material, such as dried leaves. You can read how to compost properly here .
For a standard compost pile measuring 90 x 90 x 90 cm, this means no more than 570 cups of used coffee grounds. As you can see, it would be quite difficult to exceed this limit.
90 x 90 x 90 cm = 0.72 cubic meters
20% of this is 0.144 cubic meters
Since 1 cubic meter = 4000 cups, that makes about 570 cups of coffee grounds
When and how often should you fertilize your tomatoes with coffee grounds?
You can use coffee grounds when you plant the young plants outdoors and 1-2 times per month thereafter. Typically, most plants prefer fertilizer in their growing season, just before they set fruit, but any other time is fine.
Be careful not to use too much coffee grounds as this will affect the frequency of application. Check the pH of your soil regularly.
Here’s how to fertilize tomatoes with coffee grounds:
- Add composted coffee grounds to the planting hole to improve the soil composition. It will act as a slow-release fertilizer, providing nitrogen to the soil for several weeks.
- Mulch tomatoes with composted coffee grounds (or coffee grounds + mulch) throughout the summer to retain moisture in the soil, prevent weeds and add nutrients to the soil.
- Work the coffee grounds into the soil in the fall and allow them to decompose directly into the soil. Experts recommend enriching the soil twice a year with organic material such as compost, manure or coffee grounds.
- For tomatoes in pots: mix coffee grounds and soil in a 1:1 ratio and add the mixture to the pot so that the soil is completely covered. Always allow the coffee grounds to dry out thoroughly before use to prevent mold growth.