Should You ‘Water’ Your Plants With Leftover Coffee (and Other Drinks)?

Should You ‘Water’ Your Plants With Leftover Coffee (and Other Drinks)?

We’ve all wondered as we carry a bunch of mostly-empty glasses and mugs from the workspace to the kitchen: What would happen if I dumped these in my pothos plant?

Probably nothing — at least not right away. While some common drinks should never be used to “water” plants, others are harmless, or even potentially beneficial. It all depends on what types of compounds a beverage contains.

Seltzer: Perfectly fine

All beverages are mostly water, but seltzer — even flavored kinds — is really close to plain tap water. It’s definitely more acidic thanks to the carbonation and flavoring essences, but most plants grow best in mildly acidic soil anyway, so that’s not necessarily a bad thing. (Potting soil has a pH of between 6-7, and it’s usually closer to 6.) An ounce or two of flat pamplemousse LaCroix is harmless, especially if you dilute it with tap water before pouring it onto your plants.

Plain tea and/or coffee: Good, actually

Our favourite caffeinated beverages are just dead plant matter and water, which happen to be two of the three things growing plants need. (Light is the third.) Said dead plant matter contains small amounts of essential nutrients like phosphorous, nitrogen, and potassium, which make the resulting beverage slightly acidic. Basically, leftover tea or coffee is a very weak fertiliser.

Keep in mind, though, that this only works if you take your tea and/or coffee black. For reasons that will soon become obvious, sweeteners and creamers should never go in your plants — especially if they live in your house.

Booze, juice, dairy, and other sweet or fatty drinks: Hard pass

If you’ve ever chickened out of dumping the dregs of a wine bottle into your ficus, your instincts were right on — even if your reasoning wasn’t. Ethanol isn’t all that bad for plants in low doses, but the sugars and other carbohydrates in alcoholic beverages (and others) definitely are.

Plants have no use for the carbs, fats, and proteins that make food nutritious to humans. While a little bit of sugar isn’t an immediate death sentence, over time, giving plants nutrients they can’t and won’t use will kill them — if the pests they attract haven’t already finished the job. Insects love sugar, yeast, fat, and anything else they can scavenge; dumping beverages with those ingredients into a small amount of potting soil is an ant or fungus gnat infestation waiting to happen.

If the idea of watering your plants with anything but pure water still makes you nervous, you certainly don’t have to do it. But if you’re constantly leaving mugs with an inch or two of coffee around the house, this is a good way to put that liquid to good use. Just remember that the dose makes the poison: When in doubt, dilute the (sugar/dairy-free) beverage with tap water and spread it around to multiple plants.

Log in to comment on this story!