Indoor gardening is all about sharing: the sharing of plants and the sharing of information about them. Much of the information sharing takes place online—where gardeners can access a wealth of information and/or fall into a trench of deception. It’s kind of a crap shoot whether a google search comes up with dubious myths or accurate science. One of the internet plant myths that won’t die is using kitchen trash in your plants.
I’d say the most popular trash-for-plants myth is soaking banana peels in water and using that to water your plants. As a daughter of a former banana farmer, I am no stranger to the 101 things you can do with bananas. But never did we use banana as a fertilizer. First off, in order to be classified as a fertilizer, there has to be an NPK value, three macronutrients essential to plant health – nitrogen, phosphorous, and potassium. These are often represented by little numbers on fertilizer containers. Bananas have no NPK value and therefore cannot be classified as a fertilizer.
Bananas are known to be packed with nutrients, especially potassium, but did you know dozens of other fruit and vegetables contain MORE potassium than bananas? A medium sized baked potato has twice as much potassium as a banana. Avocados, papayas, pinto beans, and tomatoes (this list goes on and on) also have more, but you won’t find internet advice about adding these to your houseplant water. I suppose bananas are more fun.
Additionally, as bananas break down, they will eat up nitrogen in the soil that’s vital for plant growth. This is true for a lot of food waste. In the long run, it can inhibit plant growth. Not only that, banana water is a great way to attract fungus gnats into your house, which is one of the top houseplant problems people also google about (and receive false advice as a result—saving this for a future rant!).
Egg shells and coffee grounds are also commonly hyped up as great additives to houseplants and garden beds. These, too, should be avoided for similar reasons. They contain minimal nutrients and do little to benefit your plants.
Coffee grounds in particular cause more issues than benefits. Caffeine may be great for humans (debatable), but it’s bad for plants. The extra boost we get can do the exact opposite for plants, actually inhibiting growth in many species.
Perhaps the reason more people are trying to utilize material like this in plants is because of the noble call for sustainability. But matter like coffee grounds, eggshells, and banana peels quickly break down in compost piles. There are better ways to be more sustainable in our plant-keeping —and that’s another rant for the future.