Houseplant pests series part 1: Soil or fungus gnats

This is my first in a series of posts about common household pests. I am starting with soil gnats (also referred to as fungus gnats) because in my opinion, these are the most common houseplant pests. Unlike most houseplant pests, which usually only effect certain types of plants, soil gnats can effect any plant that is potted in dirt. 

Soil gnats

You will notice them crawling or flying out of the soil around your plant when you water or otherwise disturb the soil. 

Soil gnats look similar to fruit flies, and I have seen many people mistaken a soil gnat problem with fruit flies. 

Soil gnats lay their eggs in moist soil where the larvae will hatch and feed on small roots, fungus and other organic matter in the soil. 

They are mainly just a nuisance and are rarely destructive to the plant. Sometimes they can cause root damage if the infestation is heavy, but normally they only eat rotting roots.  

A soil gnat infestation can come from anywhere. They can be in the soil of a newly purchased plant or a bag of potting soil, they can come in with a plant that was outside during the summer, they can even come through the screen of an open window during the summer. Even if you are successful in eliminating an infestation from your house, recurring problems with soil gnats are difficult to prevent. The good news is that soil gnats are one of the easiest houseplant pests to control. 

Soil gnats are difficult to eliminate if you have a large number of plants. The adults can easily fly or jump from one plant to the next, laying eggs wherever they find moist soil. Like fruit flies, the adult gnats only live for a few days. Once all the larvae are dead, your problem will go away. 

As I stated earlier, soil gnat larvae thrive in moist soil. Actually, they can’t even survive in dry soil.

Sticky paper fly trap to capture soil gnats

Therefore, the easiest and most effective way to control and ultimately eliminate soil gnats is to make sure you do not regularly overwater your plants. 

 Always check the soil before you water a plant by sticking your finger into the soil. 

Do not water the plant if the top inch of dirt is moist. 

Be careful though, you don’t want to allow the entire root ball to dry out on most houseplants; and you definitely don’t want to wait until the plant has wilted before watering it. 

Here is a list of other things you can do to control a soil gnat infestation:

• Water the plant from the bottom. Soil gnat larvae live in the top inch of the soil. Watering from the bottom will make it easier to maintain dryer top soil without risking the overall health of the plant.
• Put a fly trap near the plant to capture the adult gnats. Note that this will only be effective to control the adult population, it will not take care of the problem at the source (the larvae).
• Pour or spray insecticidal soap into the top of the soil to kill the larvae. This should be effective after a few treatments. You can also use a mixture of dish soap and water rather than an insecticidal soap.
• Remove the top inch of soil and replace it with new, dry soil. This will remove the eggs and larvae. The larvae could still hatch and mature in the soil after you remove it, so make sure you remove the soil from your home immediately.
• Replace the top inch of soil with a layer of sand, gravel or decorative moss. This will help detour the gnats from laying eggs in the soil, and also adds a decorative touch.
• Store potting soil in a sealed container. I store mine in buckets that have a tight lid rather than in the bag it comes in. Also, don’t store potting soil outside in the summer.

Please feel free to leave a comment and share your tips on how you deal with soil gnats. I would love to get more ideas from others out there that have found a better way!

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Pesty Pests

I constantly get questions regarding houseplant pests. Now that the busy holiday season is over and we are officially in the dead of winter here in MN, I thought it would be a good time to write about my experiences in dealing with common houseplant pests.

Houseplants

Though houseplants can become infested with pests at any time during the year, winter is when they are most susceptible. There are several factors involved here. 

• Houseplants go into a state of dormancy during the winter, which can make them more prone to attacks from pests.  
• Winter growth on a many houseplants is weaker than it is in the summer, making it more vulnerable to infestation.  
• Humidity levels are much lower in the house during the winter, which is the perfect breading ground for pests like spider mites. Plus, your plants don’t get any fresh air.   
• Pest infestations are worse in the house than they are outside because there are no natural predators to control the pest population (unless you raise lady bugs, or other beneficial bugs – which some people do!).

Aphid infestation

Many of you may have already had issues with a pest infestation, and never realized it. 

Maybe you had a plant that seamed perfectly healthy one day, then the next day it started to die and you couldn’t figure out how to save it. 

(On several occasions, I have found infestations on friends or family member’s houseplants that they didn’t even know they had.)

Or maybe you had a plant that you knew was infested, but you didn’t know what to do - so you just threw it out.  

Scale infestation

If you have houseplants, at some point you will have to deal with pests. 

It just goes with the territory. 

The best defense against any houseplant pest infestation is prevention. 

Over the years, I have dealt with many pest infestations, and have learned ways to prevent/manage them.



Here is a list of general pest prevention/management tips...

• Keep it sanitary - Always clean and disinfect pots before reusing them. I like to use the dishwasher for this task.
• Keep it fresh – If you're repotting a houseplant, it's fine to reuse the soil in the new container for the same plant. However, you should never reuse potting soil from one plant to repot another plant. If the plant that you are repotting has recently had a pest infestation, it is a good idea to remove and discard as much of the soil as you can and replace it with fresh soil. This can help prevent a future infestation; however I do not recommend repotting a plant just because it has a pest problem. Repotting can further stress an unhealthy plant, which could ultimately be fatal to the plant.
• Keep it sterile - Always use sterile, commercial potting soil when you pot your plants; and never, never use garden soil! Most common houseplant pests live and breed in soil. Also be sure to sterilize your clippers and other tools each time you use them. You can wash them with soap and water, or you can dip them in rubbing alcohol between uses. Be sure to wash your hands after handling an infested plant.
  
• Keep it in check - Inspect your plants on a regular basis for signs of pest problems, I usually do this each time I water my plants.
• Keep it clean - If you find any pests on your plants, be vigilant in fighting them. Inspect the plant daily and continue to treat the plant until all signs of the infestation are gone. Most common houseplant pests multiply very quickly, and take several treatments to control or eliminate.
• Keep it isolated – If you find that one of your plants has a pest problem, isolate it for several weeks during treatment. Additionally, when you bring home a new plant, make sure that you inspect it closely for any signs of pests; it’s also good to isolate new plants for a few weeks to make sure no infestation shows up. I have brought plants home before and didn’t check for pests, only to have an infestation a few weeks later which, in some cases, spread to surrounding plants.

Mealy bugs

Stay tuned! I plan to write a series of posts that will discuss several common houseplant pests, and my experiences with trying to control or eliminate them. The pests I will discuss in this series include spider mites, whiteflies, scale, aphids, soil gnats and mealy bugs. Yuck, yuck, yuck, yuck, yuck and yuck!

Please feel free to add comments about your own experiences. I find that the best advice comes from fellow gardeners! I am also happy to answer any questions you may have. Thanks for reading!

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