Will Gnats Kill My Plants? How To Protect Your Plants

Two black gnats with yellow bellies on a plant.

At one time or another, we’ve all been annoyed by tiny little gnats hovering around us while we try to enjoy time outdoors.

While we can simply swat them away or move to another area, our poor plants are rather defenseless.

Although gnats pose no threat to people or pets, having them buzz around your plants may be more than just annoying.

Will gnats kill my plants? Fungus gnats seek out damp soil to live and nest. Female gnats lay between 100-300 eggs in the plant’s soil. Once hatched, gnat larvae feed on soil fungus and plant roots. Left unchecked, they can cause fatal damage to the roots, resulting in plant death.

Aside from the nuisance factor, should you be worried that these pesky bugs will kill your plants?

Find out what you can do to prevent harmful gnat invasions from threatening the health of your plants.

Don’t miss our Complete Guide to Getting Rid of Gnats for a comprehensive approach to banishing gnats from your home and yard.

Gnats Love Moist Potting Soil

Fungus gnats are tiny black insects, only about 1/4 inch long, whose larvae pose a potential threat to the health of your plants.

Although gnats have a short lifespan of only about seven days, a female gnat can lay hundreds of eggs at a time in plant soil.

The eggs hatch within a couple of days, and the larvae love to munch on fungus found in the soil, any decaying organic matter, and the roots of the plants. 

Damage to the plant’s root system may vary depending on the severity of the gnat infestation, but any damage will weaken the plant, making it more prone to disease and less likely to thrive.

Heavy gnat infestations can be enough to kill the plant entirely.

Gnats in the Home

The more you water your plants, the more fungus gnats will thrive. They are attracted to and love to live in extremely moist, overly watered soil.

You know you have a problem if you see gnats flying out from the soil every time you water the plants or move the plants while dusting.

Should you worry about getting bitten? Find out here.

Houseplants

Gnats aren’t picky about the type of houseplant they find because it’s the moist soil they seek out.

Adult gnats aren’t the issue; rather it’s the larvae that feeds on a plant’s roots.

Overwatering plants can also result in root rot, resulting in another gnat larvae feeding favorite, decomposing roots.

They start by feeding on root hairs, but with a large enough larvae population, they will move on to the actual roots or the plant itself.

What you will notice is the plant wilting, stunted growth, or yellowing, malnourished, dropping leaves.

Herbs

While there’s nothing better to cook with than fresh, home-grown herbs, gnats will still be attracted to the moist soil, any decaying organic matter, and root hairs. 

If growing herbs from seed, small plants and seedlings are particularly susceptible to damage from feeding gnat larvae.

How to Prevent Gnats in the Home

Gnats can get into your houseplants from various sources (we explain in more detail here).

The purchase of a new plant (especially one that has been kept outside), a new bag of potting soil, or even gnats flying through an open door is all it takes for them to take up residence in your houseplant soil. 

The two main points of eliminating gnats is to keep plant soil as dry as possible and kill gnats in the larvae stage to break their life cycle. 

Here are some tips to kill gnats in the larvae stage:

  • Add a shallow layer of horticultural sand to the topsoil layer of potted plants, which is good for drainage, keeps top layer of potting soil dry, and discourages females from laying eggs.
  • Remove dead leaves and other organic matter from plants to eliminate the gnat larvae food source.
  • Cut a potato in half. Face cut side down in the soil to attract larvae as an alternate food source. After a few days, seal potato in a plastic bag and discard.
  • Mix four parts water with one part peroxide. Pour mixture over the plant soil until water drains from container. This helps kill soil fungus and kills gnat larvae immediately.
  • Drench soil with diluted Neem oil (this one is organic).
  • Sprinkle plants with Ceylon cinnamon, a natural fungicide that kills the fungus that gnat larvae eat.
  • Spritz essential oil sprays near gnat-infested areas. Gnats hate the scent of lavender and lemon, and they hate vanilla extract as well.
  • Sprinkle coffee grounds on the top layer of potted plant soil.

Also consider placing a sticky trap or two (these come in whimsical shapes and work very well) at the base of each plant.

For a more aggressive approach, you could use one of many pesticide sprays, some of which are even organic. We give you our top recommendations in this article.

You could also start growing herbs to combat gnats. Sound counterproductive?

The gnats, while still attracted to the moist soil, will be too repelled by the scent of certain herbs to bother with the plants.

Herbs that are delicious for cooking but unpleasant to gnats include:

  • Basil.
  • Lavender.
  • Lemon Thyme.
  • Chives.
  • Rosemary.
  • Mint.
  • Bay laurel.

Fun Fact: Bounce Dryer Sheets repel fungus gnats too (find them here on Amazon).

Gnats in the Greenhouse

Gnats love the outdoors and all the moist soil that comes with the territory.

If you have a greenhouse with a lot of plants, be especially mindful of gnats living in the soil of any kind of potted plant you have outdoors.

Greenhouses are typically kept at warmer, more humid temperatures, creating the perfect breeding and feeding environment for gnats.

Check your plants carefully and routinely, and take note if you notice any gnats quietly buzzing around your head – a sure sign of a larger problem.

Be sure to stop by our gnat section for a complete list of all of our gnat-focused articles.

Types of Plants

Shrubs

Shrubs attract gnats due to the moisture-rich soil conditions most require to grow.

Shrubs require frequent watering, and female gnats look for such an environment to lay eggs.

Most shrubs require an inch or two of mulch once planted, and gnats are attracted to the moisture and fungus that often results.

Trees

Tree saplings are particularly susceptible to gnat larvae damage because the roots are not as strong as more well-established trees.

Because saplings require more water than houseplants or other types of plants, gnats will migrate towards those that offer the most well-watered conditions. 

Fruit trees are a big draw for gnats, as is any wet mulch around the base of a tree.

Seedlings

Any type of plant that is grown from a seedling is far more susceptible to becoming damaged, stunted, or killed if the larvae population of gnats infests the soil.

Keep an extra watchful eye on seedlings to protect them from this damage. 

If you notice gnats flying around plants in a greenhouse, larvae are present. Protect seedlings with either:

  • Gnat traps – simply place these whimsical, yellow sticky traps into the soil and watch how many gnats are drawn in to their death.
  • Organic insecticides – these are typically botanical insecticides made with naturally occurring insect killers. This one is made from chrysanthemums and can be used up until the day of harvest.

How to Prevent Gnats in the Greenhouse

There are several things to keep in mind to control a fungus gnat population in a greenhouse:

  • Monitor humidity levels as gnats thrive in the warm, humid conditions necessary to maintain moist soil.
  • Do not overwater plants.
  • Remove standing water in bottoms of plant containers and watering cans.
  • Dry puddles from dripping hoses or after watering.
  • Don’t store compost or any decomposing organic materials inside a greenhouse.
  • Seal extra mulch and potting soil in covered plastic containers.
  • Use an organic pesticide, like this one, or neem oil to kill both gnats and larvae.

Gnats in Outdoor Gardens

Gnats can be found outdoors anywhere there is moist soil and decaying organic matter.

It’s important to keep gardens well manicured and remove any dead or dying leaves, stems, or flowers. 

Remove wilted or dying plants because gnats, in addition to other garden-harming insects, will jump on the opportunity to feed on these plants.

This almost guarantees an infestation that could threaten the health of all the rest of your plants.

Flower Beds

Adult gnats are attracted to and feed on flowers. They can’t resist the sweet scent and will live in your flower beds.

Flower beds provide the perfect environment of the moist soil conditions and a food source, both of which they need to live and reproduce.

Vegetable Gardens

Gnats are attracted to vegetable gardens as they also provide a food source and moist soil where they like to live.

Any decomposing vegetables or parts of vegetable plants are a prime source of food for gnats.

At some point, it may be necessary to use an organic pesticide on fungus gnats rather than risk losing your plants.

Using an organic pesticide allows you to kill gnats and larvae while still enjoying a safe, bountiful vegetable garden.

This organic option uses rosemary, clove, and peppermint essential oils to effectively eliminate and repel soft body insects such as gnats, yet is safe to use and won’t harm beneficial pollinators.

Earth's Ally Insect Control Spray | 24 fl. oz. Ready-to-Use | Safe Insecticide for Garden | Pet Safe | Bee Safe

Check Price on Amazon

Raised Garden Beds

Just because your garden isn’t in the ground doesn’t mean it’s safe from gnats. The important thing to remember about raised garden beds is proper drainage.

Keep the first inch or two of soil as dry as possible and do not overwater plants.

Potted Plants

As with any indoor potted plant, the number one issue is that gnats are attracted to fungus and moist conditions in the soil.

Outdoor potting soil tends to have a greater chance of containing fungus due to all the exposure to outside elements and fungi sources. 

Keeping plants well pruned, removing dead organic matter, and keeping the soil as dry as possible will help prevent gnat larvae from taking over the soil and roots of outdoor potted plants. 

How to Prevent Gnats in Outdoor Gardens

Promptly removing all decaying and decomposing matter from the area will go a long way in preventing gnat infestations. Also:

  • Eliminate sources of overly wet soil or standing water.
  • Correct any leaks or drainage issues that promote extremely wet or moist soil conditions.
  • Plant things gnats hate, such as marigolds; decorative grasses, like lemongrass or citronella grass; and herbs, such as lavender.

Read through our list of recommended traps and sprays to discover both natural and chemical solutions for outdoor gardens.

Gnats in the Yard

If you are attracting gnats to your yard, the odds of them getting into the outdoor gardening areas is a given.

Remove the sources of attraction and you will have more enjoyable time spent outdoors without annoying gnats, while reducing the odds of them coming inside your home.

Sources of Attraction

  • Garbage cans
  • Recycling containers
  • Compost bins
  • Bright yard lights
  • Wet grass, leaves, and weeds
  • Messy gutters
  • Wet mulch
  • Leaky hoses
  • Birdbaths
  • Gardens, plants, trees, and shrubs in overly watered soil
  • Condensation around doors, windows, and air conditioning units

How to Prevent Gnats in the Yard

The most important prevention method is to maintain dry, clean yard conditions.

  • Keep your yard and garbage bins clean. 
  • Keep garbage cans covered. 
  • Store extra mulch and potting soil in sealed, covered plastic containers. 
  • Remove and dispose of any decaying organic matter.

Again, check with our recommended products for treatment options.

Wrapping It Up

By keeping your outdoors neat and dry, you help keep the gnat population down. This decreases the odds of gnats getting inside your home. 

If and when you notice gnats circling plants, take immediate action.

By using natural traps, commercial gnat traps or environmentally friendly insecticides, it’s easier to disrupt the life cycle of gnats and extinguish them during the critical larvae stage.

By putting these gnat-busting tips to good use sooner rather than later, you can avoid a lot of headaches, prevent potential damage to your prized houseplants inside, and enjoy a beautiful, gnat-free outdoor oasis.

If you’re like most people suffering with a gnat problem, you probably have additional questions or would like more advice for eliminating them entirely.

Head on over to our gnat page for more tips, strategies, treatment plans, and recommended products. Click here for access to all of our gnat articles.

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