Diluted Coffee For Plants: Can You Water Plants With Coffee

Table With A Coffee Cup Book And Small Potted Plant
plant coffee
(Image credit: byryo)

Many of us start the day with some sort of coffee pick me up, whether it's a plain cup of drip or a double macchiato. The question is, will watering plants with coffee give them that same “perk?”

Can You Water Plants with Coffee?

Coffee used as a fertilizer is not exactly a new idea. Many gardeners add coffee grounds to compost piles where it decomposes and mixes with other organic matter to create some fantastic, nourishing soil. Of course, this is done with grounds, not the actual cold cup of coffee sitting here at my desk. So, can you water your plants with coffee proper? Coffee grounds are about 2 percent nitrogen by volume, nitrogen being an important component for growing plants. Composting grounds introduces microorganisms that break down and release the nitrogen as it raises the temperature of the pile and aids in killing weed seeds and pathogens. Very useful stuff! Brewed coffee also contains measurable amounts of magnesium and potassium, which are building blocks for plant growth as well. Therefore, it seems a logical conclusion that watering plants with coffee might indeed be very beneficial. Of course, you wouldn't want to use the cup sitting in front of you. Most of us add a little cream, flavoring, and sugar (or sugar substitute) to our Joe. While real sugar would not pose a problem to the plants, milk or artificial creamer won't do your plants any good. Who knows what effect any of the many artificial sweeteners on the market would have on plants? I'm thinking, not good. Be sure to dilute before watering plants with coffee and don't add anything else to it.

How to Water Plants with Coffee

Now that we have ascertained that we should use diluted coffee for plant fertilizer, how do we do it? Coffee has a pH of from 5.2 to 6.9 depending on the variety and preparation. The lower the pH, the more acid; in other words, coffee is pretty acidic. Most plants grow best in slightly acid to neutral pH (5.8 to 7). Tap water is slightly alkaline with a pH greater than 7. Therefore, using diluted coffee for plants can increase the acidity of the soil. Traditional chemical fertilizers, the addition of sulfur, or allowing leaves to decompose on soil surfaces are methods to decrease soil pH levels. Now you have another option. Allow your plain brewed coffee to cool and then dilute it with the same amount of cool water as coffee. Then simply water acid-loving plants such as:

Water with the diluted coffee just as you would with plain tap water. Don't use this to water plants that do not like acidic soil. Don't water every time with the diluted coffee fertilizer. Plants will sicken or die if the soil becomes too acidic. Yellowing leaves may be a sign of too much acid in the soil, in which case, abandon the coffee irrigation and repot plants in containers. Coffee works great on many types of flowering indoor plants but can be used outside as well. Diluted coffee adds just enough organic fertilizer to encourage bushier, healthier plants.

Amy Grant

Amy Grant has been gardening for 30 years and writing for 15. A professional chef and caterer, Amy's area of expertise is culinary gardening.