bad at plants

Help, My Plants Keep Spawning Gnats

Photo: Getty Images

Welcome to Bad at Plants, a new column in which plant expert Maryah Greene, of Greene Piece consulting, answers your questions about plants, so that we might all become at least slightly better at keeping them alive.

“I recently became a houseplant person (yay!) and have quickly accumulated 17 plants, 10 of which I keep in my kitchen. My oldest plant is a quite long trailing pothos that I inherited from a friend about four years ago (when I didn’t know what I was doing; it’s a miracle I kept it alive for that long). Now that I’m learning the ropes of the plant lifestyle, I am attentive to bugs/pests, and have noticed tiny black bugs flying around the soil and leaves closest to the soil. I tried spraying all of my plants (because I know one plant’s bugs can infect all the rest) with neem oil diluted in water, and staking those sticky yellow butterfly-shaped traps into the soil. The sticky trap in the pothos filled up quickly, and I replaced it, but I’m wondering if I’ve done what I need to do and now I just have to be patient and wait, or if I need to take more drastic action. Also, do I keep watering it as usual? Do I modify my behavior at all? Do I dig out the larvae?”

This is a great question, and one I get a LOT in my Instagram DMs. The water schedule is the biggest thing that needs to be changed once you start to see those gnats. They like moisture in the soil. With a pothos plant, let’s assume you’re watering it once a week. I would move to every ten days to every two weeks. We want the soil to completely dry out — not to the point it’s harming the plant, but so that all the excess can get out of there. The roots are really not happy right now, and we don’t want them to become moldy. Moldy roots is the second stage of a waterlogged plant. Gnats are the first.

I promise it’s okay to completely dry out a plant’s soil if it means ridding a plant from a pest infestation. It may even be worth completely repotting the plant in fresh, insect/pest-free soil after the plant shows some signs of normalcy. There are a ton of insect repellents out there, but nothing will truly help your infected plant more than reducing the amount that you water it. For example: a pothos that is being watered every three days (WAY TOO OFTEN — it should be more like every seven to ten days) should have a significant change in watering schedule once pests/fungus are found. Rather than three days, try watering every 15 days. When pests and fungus subside, move to a regular seven to ten day schedule and stick to it.

The other thing that goes along with this is that the plant might not be getting as much as light as it needs. Your watering schedule is based on how much light you’re getting, so the water has to go through the plant or evaporate on top. If you’re not getting a lot of sunlight, that evaporation won’t happen. I’m currently living in a basement, so gnats are just a part of my life. I just deal with it, and I have those sticky traps everywhere. I don’t get a lot of sunlight to burn that top layer off.

You mentioned neem oil — the plant shop I partner with, Rooted NYC, recommends neem oil all the time. It’s a great solution, but it won’t do anything unless you change the watering schedule. The neem oil can only do so much. If your gnat problem isn’t crazy, I’ll often recommend starting with cinnamon — sprinkling just a little on the top layer of soil. If it’s worse, I’ll recommend neem oil, and if it’s really intense, I would take the plant outside and inspect the entire thing. That’s a whole other road you have to go down. For you, it sounds like neem oil is the right thing to do, plus adjusting your watering.

I also have a bowl I’ll fill with apple cider vinegar and dish soap. The vinegar attracts the flies, and the dish soap gets them stuck in there. I put plastic wrap on top with a couple holes, so they can get in, but it’s hard for them to get out. That also helps, but it’s not preventative.

You asked about pothos. Pothos are what I call a speak-to-you plant. The leaves will tell you everything you need to know, versus, like, cacti, where you’ll have no freaking idea. When your pothos’s leaves droop, they’re telling you they’re unhappy. A little drooping is okay, but browning and yellowing is when we get concerned, and when you need to modify your watering schedule and/or your sunlight.

Help, My Plants Keep Spawning Gnats