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How to Fertilize Your Houseplants

When I first started collecting plants, I certainly was not thinking of all of the maintenance tasks I’d have to start doing. The biggest and scariest one for me was fertilizing.

There are just so many fertilizing options out there. Not only that, but there are soil conditioners, foliar sprays, root hormones, and pretty much every chemical you can think of to stimulate growth. So which one was I supposed to use and how often?

If you’ve looked at fertilizer, you’ve probably seen the letters NPK. NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K). So what do these things do? Nitrogen helps the leaves of a plant grow and is responsible for making plants greener. Phosphorus helps root growth, flowering, and fruiting. And Potassium helps with the overall health of the plant, helping prevent disease and strengthening the durability of the plant.

Your plants crave Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Potassium. These last three come from the soil, so the health of your potting mix is vital for the health of your plants. Different fertilizers offer varying ratios of these nutrients. And you are going to need a different percentage depending on what you are growing.

For this blog, we are going to focus on houseplants. You’ve probably seen advertisements for soil conditioners like Superthrive, Liquidirt, and Noot. These are actually soil vitamin supplements and not fertilizers.

Soil conditioners alone are insufficient for a complete fertilizing regimen. That’s not to say that these products aren’t great. For reviving stressed plants or rooting cuttings, they can be awesome. But for a complete food source for your plants, they are just not enough.

For my personal collection and for the plants that I grow for sale, I use a mixture of long-term release fertilizer, fish fertilizer, and worm castings in my potting mix.

For a long-term release fertilizer, I use Osmocote Plus. I like this option because it is something that is always in the soil of my plants. Every time you water your plants, a little bit of the nutrients dissolves into the soil—an excellent option for those of us that tend to forget to fertilize regularly.

During the growing season, I supplement the long-term release granules with fish fertilizer. I use Neptune’s Harvest Organic Fish Fertilizer. Be warned that it can be a bit stinky if you apply it inside, but it is SO WORTH IT. My plants absolutely love it, and it comes with easy directions to follow.

earthworms on a persons hand
Photo by Sippakorn Yamkasikorn on

In my potting mix, I use a mixture of worm castings to build my soil. I like the Wiggle Worm brand. For those that don’t know, worm castings is pretty much just worm poop. I highly recommend adding some to your potting mix whenever you repot a houseplant.

What is great about these three options is that I have yet to experience fertilizer burn. Fertilizer burn happens when you overfertilize a plant. It just causes your leaves to show damage, which is especially sad when you are just trying to feed your plants.

If you are looking for a full rundown of how fertilizer works, I highly recommend Summer Rayne Oakes’ video Houseplant 101: Complete Guide to Fertilizing Houseplants.

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