There are little bugs flying around my houseplants. I did some research online and found out they are called “fungus gnats.” Help!

Rachel

Brooklyn, NY

Dear Rachel,

Fungus gnats are pesky and common—most people who have houseplants encounter them at one time or another. But don’t worry! There are solutions.

A flying insect with a dark body and two translusent wings against a white background.
The mighty fungus gnat, from the family Sciaridae. Image by B. Schoenmakers at Waarneming.nl via Wikimedia Commons.

The larvae of fungus gnats can chew on and damage plant roots, so they’re not ideal visitors. Still, it may be helpful to think of fungus gnats as a symptom rather than the root problem. If you address the underlying issue, the gnats will go away.

Have you ever had fruit flies? If so, you know that once you get rid of their food source and breeding ground (ripening or decaying fruit), they go away on their own. The same is true for fungus gnats. The main trigger of a fungus gnat infestation is overwatering, because fungus gnats thrive in soggy environments. Larvae feed on decaying organic matter in moist soil. The best cure is to allow your soil to dry out between waterings. Most houseplants are happier in these conditions, so this step alone can work wonders.

If letting your soil dry out between waterings doesn’t seem to reduce the fungus gnat population, the next step is to check for root rot. Gently remove your plant from its pot. If the soil smells bad or if the roots look mushy, dark, or slimy, you probably have root rot.

As long as you still have some green growth on the aboveground plant parts, your plant is likely still salvageable. Trim away the rotten-looking roots, leaving any firm, light-colored roots. Discard any foul-smelling soil. Repot the plant with fresh, sterile soil after thoroughly washing the pot. If you want to invest in extra protection against fungus gnats, you can buy sticky traps to control the adult population. These are adhesive-covered cards you can put around your plants to trap and kill the adult gnats.

A black pot with soil contains two yellow squares with tiny black bugs on them.
Sticky traps can help control the adult population. Photo by Maja Dumat via Flickr.

To prevent future problems, take a step back and consider your watering routine.

For the majority of houseplants, water when your plant’s soil is dry to the touch to a depth of about one knuckle. Some plants may need more or less frequent watering, but this is a good rule of thumb to start with—you can adjust after observing your plant’s response.

Also be aware that your plants’ watering needs will change over time, so watering on a strict schedule can actually cause problems like fungus gnats. I often hear from people who have fungus gnats in the winter. This is usually because they are watering once a week rather than when their plant’s soil is dry.

In winter, plants use less water due to lower light and slower growth. As the sun’s rays weaken in the winter months, the soil isn’t drying as quickly—and if you don’t adapt your watering to the changing conditions, the soil becomes waterlogged, which is exactly the kind of situation fungus gnats love.

With a little attention to watering and some proactive measures, your plant should recover beautifully, and the gnats will be a distant, pesky memory.

How do I know when it’s time to repot my houseplants? How do I repot them?

Amira

Brooklyn, NY

Dear Amira,

Although plants cannot speak to us with words, they can tell us what they need in other ways. Here’s how to tell when it’s time to repot:

  • The roots are peeking out of the drainage hole on the bottom or visible on the soil surface.
  • The water rushes quickly through the pot when you water it (indicating the soil is so root-filled, it’s not holding water anymore.
  • Your plant seems to dry out much more quickly between waterings than it used to.
  • Your plant is top-heavy and seems inclined to tip over.

If you see any of these signs, it’s time to repot. Here’s how:

  1. Prepare your plant. Water your plant about 30 minutes before repotting.
  2. Choose the right pot. Pick a pot 1–2 inches larger in diameter than your old pot.
  3. Prepare the pot. Put some fresh soil at the bottom.
  4. Remove plant from old pot. Gently loosen your plant from its current pot and lift it out.
  5. Position and fill. Place your plant in the center of its new pot, and fill all around it with fresh potting mix. Leave space at the top so you can water it without overflowing. Tap the pot firmly on your potting surface to remove any large air pockets.
  6. Water thoroughly. After watering, the soil may settle more, so fill in any additional potting mix needed to make sure your plant is potted at the same level it was in the old pot.
  7. Return to its original location. Repotting can be stressful for plants! Keeping it in its familiar location can help it adjust.

Unless your plant is truly bursting at the seams, I recommend waiting until spring to repot. When the sun gets stronger and the days get longer, your plant will grow more vigorously, and it will be easier for it to recover from the shock of repotting than during the winter months. 

How can I tell if my indoor plants are getting enough light, and what are some low light options?

Wen

Woodside, NY

Dear Wen,

Whether you are gardening indoors or out, the most important step for success is to make sure you are putting the right plant in the right place. When gardeners think about the “right place” for any given plant, sunlight is one of our first considerations.

You will know that your indoor plants are getting enough light if they have:

  • Healthy, vigorous growth.
  • An upright form. If your plants seem to be leaning toward the light, they probably need more than they are getting.
  • Vibrant leaves. Yellowing or dropping leaves are cause for concern.
  • Proper spacing between leaves. If your plant has long gaps between leaves (aka, is “leggy”) it is probably not getting enough light.

If you think your plant is not getting enough light, moving it to a higher exposure area can help. In our area, southern and western exposure windows will have more light than eastern or northern ones.

(I do not recommend using supplemental plant lighting, because it’s just not a sustainable long-term solution. You’re better off placing your plant in the right conditions.)

Two potted plants with large bright green striped leaves.
Cast iron plants are a good low-light option. Photo by K M via Flickr.

If you don’t have sunny areas in your home, I recommend these low-light plants:

ZZ plant (Zamioculcas zamiifolia): The ZZ plant’s upright stems and glossy, deep-green leaves give it a striking architectural appearance.

Pothos (Epipremnum aureum): This trailing plant with heart-shaped leaves is available in solid green or variegated varieties.

Snake plant (Sanseveria sp.): A low-light classic available in several different variegation patterns as well as different leaf shapes.

Peace lily (Spathiphyllum wallisii): With its dark green foliage and white blooms, this graceful plant adds an elegant touch wherever it is placed.

Cast iron plant (Aspidistra elatior): This plant is as tough as its name sounds, but it’s also charming and a worthy addition to any low-light areas of your home.

All of these plants are easy to care for and commonly available at most plant stores. Some are toxic to animals, so be sure to do your research if you have a pet at home. With their resilience and beauty, they’ll help turn your space into a cozy winter sanctuary.