I recently saw a friend empty out a remaining pot of coffee into a potted plant in their living room. While it seemed like a slightly strange thing to do, she assured me that liquid coffee can be beneficial for some plants in the right quantities. I didn’t believe her and told her so. An argument ensued. I called her crazy (I’m sorry for calling you crazy, Lisa). She told me to look it up. I looked it up. I was wrong. So here I am writing a blog post about how I was wrong. Think of this blog post as the digital age equivalent of wearing a dunce cap. I write these words with much shame and sorrow, but alas!
My research yielded three different categories of the relationship between coffee and plants: 1) coffee liquid in soil, 2) coffee grounds in soil, and 3) coffee grounds in compost. Let’s take a quick look at all three to see how they might benefit your plants and garden.
Pouring Coffee in Garden Soil
Whether or not you should pour the last remaining bit of your coffee into your garden or in your potted plants will ultimately depend on the plant’s soil preferences. Some plants love acidic soil, others hate it. Here are a few things to keep in mind:
- While I hope this goes without saying: make sure there’s no milk, cream, or sugar in the coffee before adding it to your soil.
- Don’t make this an everyday thing. If your plants jive well with acidic soil, try doing this weekly.
- If your plant’s leaves begin to drastically curl or turn yellow, this may be an indication that the soil is too acidic.
- Some acidic soil-loving plants include azaleas, Norfolk Island pines, rhododendron, African violets, and tomatoes.
Coffee Grounds Directly in Garden Soil
In essence, adding coffee (used) grounds directly to your garden soil is a way of adding organic material. While most plants can tolerate this, there are a couple things you’ll want to consider:
- Used coffee grounds aren’t acidic, making them suitable for most types of potted and garden plants.
- Fresh coffee grounds, however, are acidic, and should only be mixed in the soil of plants who thrive on acidic soil.
- As noted, used coffee grounds is organic material. Mixing it in soil will attract beneficial microorganisms, like earthworms.
- For best results, mix it in your soil well.
Coffee in Compost
In short, if you have a compost pile already up and running, there’s no reason why you shouldn’t add your coffee grounds to it. Here’s why:
- First, less space in your trash can = less space in the landfill = better for the environment. It may seem like a minuscule difference, but it adds up in the long run (especially if you’re a big coffee drinker).
- Coffee grinds add nitrogen to your compost, a necessary component in the composting chemical reactions.
- When buying coffee products—filters, K-cups, etc.—opt for compostable options, which are now widely available.
