10 Ways Prevent & Kill Fungus Gnats in Seedlings and Houseplants

If you're starting your seedlings indoors, you may have already come across some little tiny flying bugs that seem to hide in your soil. And then when you water them, they fly everywhere. They're more than just one of the most annoying bugs you can handle, especially if you're growing houseplants indoors or starting your seedlings indoors. But not only are they annoying, they can actually damage your seedlings to the point of no return. In this video, I'm going to show you 10 ways to prevent and to kill fungus gnats. Stick around. Hey, I'm Brian with Next Level Gardening. If you're looking to join an online garden community that offers tips, tricks, and support to take your garden to the next level, you're in the right place. Get started now by clicking subscribe and hit the bell so you never miss anything. Now let's get preventing and killing. So I've put together 10 solutions that run the gamut between prevention and getting rid of them if you happen to get them. And prevent as we may, a lot of times you're just going to get them anyway. So out of these 10, if you have any that you have tried with great success, let us know down in the comments. And if there's one I forgot that you've used before and it's worked, let us know that as well. We'd all like to know. So to fully understand how these preventative solutions and killing solutions work, we've really got to go back to what the life cycle is of the fungus gnat and how they work. Adult fungus gnats live for about a week. And during that week, they can lay up to 300 eggs on the surface of your soil. They hatch out in about four days and they become these little creepy crawly larvae that crawl through the soil depth of your containers. And over the next two weeks, they feed on any fungus that's on or in the soil. And they also can feed on your little seedling roots. And if it gets too bad, your seedlings are going to die. After that two weeks in the soil, they emerge as adults. And during the next week, you guessed it, each one of them are going to lay 300 eggs. So this is a problem that can get out of control really quickly. In order to prevent this or to try to prevent it from happening in the first place, the first thing you might want to do is disinfect your potting soil or your seed starting mix before you even start. So if you buy a bag of seed starting mix or you make it yourself, take a pot of boiling water and pre-moisten the soil with that boiling water. And that's going to help to kill any of the larvae that are already in the soil. The second thing you want to do, and this is for many reasons, but fungus gnats like damp soil. If the top of the soil is dry, they're most likely going to move on. And so we don't want to constantly spray our seedlings and keep everything moist. So one thing we want to do for more than that reason, but always bottom water your seedlings. So if they're in a tray already that doesn't have holes, fill the tray with water, give it about 15, 20 minutes, let them soak it up, and then remove that water from the tray. You don't want these sitting in water all the time. If you're using a humidity dome for starting your seedlings, make sure once the seedlings germinate, that dome is removed and is not put back. Now between waterings, make sure that you let the soil dry out on top. If you live in a more humid environment or if the place you've got your seeds is humid, you can also use a oscillating fan in the general area of your seedlings to just gently blow across the seedlings. That's going to strengthen your seedlings. It's also going to dry out the top, you know, quarter inch of soil. And that's totally fine. That does not mean that the seedling needs water. It is safer to let the seedlings dry out between waterings than to keep them completely wet all the time. Another preventative measure is with something you probably have around the house. Plain old cinnamon. Cinnamon is an antifungal, and just by sprinkling a layer of cinnamon on the soil, it's going to keep fungus from growing on that soil. And that is what's going to feed, the fungus is what feeds the gnats. Get rid of the fungus, lessen the chance of fungus gnats. Okay, that's enough of prevention. Now we've got to kill them. No gentle way to say that. First thing I'm going to talk about is diatomaceous earth, food grade diatomaceous earth. Now this is good for any soft bodied, creepy crawly. What it does, it feels almost like baking soda or even flour. It's even finer than baking flour. But microscopically, this is millions and millions of tiny, razor sharp particles that will actually cut into the skin of soft bodied insects. So when you're preparing your seed starting mix, just sprinkle some over the soil and mix it in. Now this isn't necessarily going to kill the adult fungus gnats, but this is going to cut into the skin of the larva. With any of these solutions, one by itself is not going to take care of the issue. Choose several, a couple of prevention and a couple of killing strategies. 300 eggs a week per fungus gnat is a lot. So we need to kill some of those adults. One way we can do that is by making a trap. I'm going to show you two different ways. So for that, we're going to need a little bowl, a little jar, some dish soap, and some apple cider vinegar. For the bowl trap, you're just going to put a half inch to an inch of apple cider vinegar, a little bit of dish soap. Set this trap in amongst your seedlings and they're going to come feed on that apple cider vinegar. That's going to attract them and between that and the soap, they're going to get trapped and killed, basically drowned. Now with the jar, we just need some apple cider vinegar, about half inch to an inch, some plastic wrap and a rubber band that I buried in there. Put the plastic wrap over the top, rubber band it and just poke a tiny slit. Again, the apple cider vinegar is going to attract them. They're going to crawl through that slit and they're going to get stuck. You might want to change these out every few days, otherwise you're going to have hundreds of tiny little ants or fungus gnats floating in them, which is kind of satisfying. But I don't know, if I saw a hundred humans floating somewhere, I probably would stay away. I don't know if they're that smart. Probably not. I know apple cider vinegar certainly wouldn't attract me to anything. The next way is with sticky traps. Now you've probably seen something like this hanging in fruit trees. Maybe you've done it yourself. I got these on Amazon. I'm going to show you also how to make a DIY version, but these are about $7 and there's 12 of these in here. I think they were $7. I'll put a link to this and anything else on my website. If you go to my website, I'll put the link below under products I love. The fungus gnats are attracted to the color yellow and so these come pre-sticky. You just peel off the coating and stick them in your seedlings. They're going to get attracted to it and stuck. If you want to make a DIY version, you can get yellow cardstock or if you go to like Home Depot in the paint section, they've got all the different colors of paint swatches. Get a couple of yellow cards. Smear a really thin layer of Vaseline onto it. Maybe glue it to a popsicle stick and stick it in your seedlings. It should work the same way. The next one is one of my favorite garden standbys and that's neem oil. You're just going to mix this. You can do it two ways. You can do a soil soak or you can spray it on the surface. I prefer a soil soak. I mix this half strength of the bottle and basically just pour it over the soil of the seedlings. Neem is an antifungal and it's also an organic insecticide. That's going to take care of the problem a couple different ways. The next solution is good old hydrogen peroxide. 3%, no stronger. Very easy to find. Most of the ones in the drugstore are 3%. You can put this on two different ways. You mix 5 to 1, 5 parts water, 1 part hydrogen peroxide and you can actually just spray the plants. It's an antifungal and then you can also spray the top of the soil. You can do this every couple of days. That's going to keep the fungus from growing and basically cut down on what the fungus net has to eat. You can also do a soil drench with hydrogen peroxide. That would be 1 part peroxide, 2 parts water and soak the entire soil with it. Just pour it right on the surface of the soil and you can do that every week or so. It's important to know with hydrogen peroxide you need to use what you mix up basically immediately. If you can't use up what you have immediately, it needs to be stored in a container that is not clear. It needs to be dark otherwise it's going to degrade very quickly and basically just become water. The last thing I want to talk about is mosquito bits. This is something maybe some of you in the south or get humid summers you already know about this out in ponds or in the gardens in bird baths and things to kill off the mosquito larva. It does the same thing for fungus gnats. You can mix this in the soil or you can you sprinkle them on top. The active ingredient in here is Bt which I've talked about on the channel many times for cabbage worms and tomato worms. Same thing Bt bacillus thuringiensis. It's a bacteria that kills them from the inside out but is harmless to humans. So like I said again don't rely on one of these methods. Pick two or three from each category and you should have no problem either preventing or getting rid of them once you have them. If you learned something from this video please give it a thumbs up. It helps a lot and I will see you tomorrow.