Don't Waste That Leftover Coffee! Turn It Into Plant Fertilizer with Diluted Coffee

That final bit of coffee left in the carafe? Instead of pouring it away, use it to nourish your plants, indoors and outside. Coffee grounds (and brewed coffee) provide plants with nitrogen, promoting lush green growth and sturdy stems. Coffee also delivers calcium and magnesium, both of which are great for plant health.

To use coffee as plant fertilizer, dilute it to the strength of weak tea. A 1:3 or even a 1:1 mix of coffee and water (depending on your coffee's strength) is about right, though you don’t need to be exact.

You can apply coffee fertilizer to your potted plants, houseplants, and even your vegetable garden. Since coffee and coffee grounds are acidic, they benefit many plants, though some plants like lily of the valley, lavender, and honeysuckle, which prefer alkaline soil, may not do well with coffee. However, many plants flourish in acidic conditions.

Here is a list from Gardening Know How of acid-loving plants that thrive with a dose of coffee, though there are many others not mentioned here:

As a general guideline, water and feed your plants once a week with a diluted coffee solution. They'll appreciate the extra nutrients and the hydration.

And while we're discussing coffee, let's take a moment to talk about those leftover coffee grounds as well.

Coffee grounds are a fantastic nitrogen source when added to soil or compost piles (though some studies, which remain inconclusive, question their direct soil effectiveness). Acid-loving plants like blueberries, azaleas, and rhododendrons will thrive as the grounds enhance soil acidity and act as a gentle fertilizer. Additionally, coffee grounds are an excellent natural repellent for pests like slugs, snails, and ants. If you're a vermicomposter, your worms will appreciate them too!