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I love watching my plants grow under my care. I hate to watch my plants slowly die outside my control because of pests. If you think pests are only an outdoor problem, think again. Likely you bought the dirt from a store where it sat in a warehouse or outside on a pallet. All sorts of critters could have come to live in the dirt before you brought it inside. (If you just went outside and dug up some dirt, ha! bug free?) Think of the last time you saw ants or spiders in your house, if they can get in so can other bugs!
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I will share some solutions I tried, what worked and what miserably failed. The two main pests I see inside are fungus gnats and aphids. In outside gardens, fungus gnats aren’t really a problem because they are really bad fliers and have short lifespans. Aphids are an outside garden problem as well and I will share some tips that translate outside for them.
These little buggers are pretty destructive and reproduce very quickly! Aphids will kill the plant and suck the sap from the stem. They don’t lay eggs, but rather give birth to live young! At least they don’t have wings. One solution for indoor growing systems in an enclosed environment if lady bugs. However, introducing a bug with wings into my apartment to eat a bug that doesn’t have wings is not my optimal solution. My carrots got very badly infected at one point. Luckily, they were confined only to one crop of carrots, but within the 6 weeks from tiny sprouts to this stage they were covered in aphids.
Before you go ripping out your entire crop, read this!
Blue Dawn Soap:
Blue dawn soap, the soap that saves the penguins from oil spills, will kill aphids! (This soap.) Gently mix a few drops of soap in some warm and gently spray your plants. The soap should kill the bugs on contact but leave the plants unharmed. This is not recommended for seedlings but works very well for older plants. Using blue dawn soap I was able to save these carrots.
I repeated the application of the soap a few times, to not overwhelm the plant as I didn’t know how it would react. After a few days, all aphids were dead. When I harvested the carrots a few weeks later, only a few manage to escape death. I thoroughly sprayed the entire surface of soil to kill any remaining. After mixing and replanting the same soil, I had no bugs remaining.
Blue Dawn Soap Rating: 9/10 Kills aphids, could be labor intensive for large crops.
In my outdoor garden, I planted marigolds along side my tomatoes to prevent aphids. Marigolds are largely touted to repeal aphids. All summer long, I had very limited number of aphids on my plants. This is a sample size of one, but it worked for me. I have not tried this inside. I plan to try it again outside next summer.
Marigolds Rating: 8/10 Repels aphids but I have a small sample size.
Now on the much harder and much more annoying fungus gnats. These tiny flies find their way into warm moist soil and reproduce rapidly. They don’t have a long lifespan, so they will also die rapidly. In my case, I was vacuuming the dead flies off the window sills weekly. Gross. Its really a wonder that fungus gnats are still alive but they have strength in numbers. They will die in a cup of water, in soap, in the sink, flying too close to the lights, sticky traps, and flying into your month. You can be a kung fu master and catch them straight out of the air (‘cause they are really bad fliers). But still after all this, they prevail.
My infestation was so bad we stopped inviting people over our apartment. We had to cover out drinks at dinner and keep a lid on any pot on the stove. It’s really a wonder Tim put up with it all as I struggled to find a solution.
Vinegar + apple slice with soap in a cup:
Google fungus gnats and you will find some people recommending to put a few drops of soap in a cup of vinegar as well as an apple slice. The flies will be attracted by the apple or vinegar and will drop into the cut. The soap will break the surface tension and the fly will die. In my opinion, this is too little too late. Also these flies will die in a cup of water or juice, so skip the fancy set up and just put a plate of water on the soil. However, this means you already have an infestation and this won’t stop the flies from laying eggs before they drown.
Vinegar soap rating: 3/10 Does kill flies but not fast enough.
Freezing the Dirt:
You may be tended to look outside at the snow and think: "I will just stick my dirt outside, the bugs will die and I can replant in the same soil." False. Fungus gnats can survive being frozen and thawed out.
Freezing the Dirt: 0/10 Does not work.
This pesticide I found at my local hydroponic store and can with the claim that all the weed growers use it to kill fungus gnats. I thought if it was good enough for commercial pot growers, then it should have no problem on my tomatoes plants! Wrong. So wrong. This pesticide is rosemary oil and is absorbed by the plant. In theory, the fungus gnats (larvae or adult) come along for a nimble they will become lethargic and wander off to die.
There are 3 main problems with this theory.
- It requires plants to work. If you have seedling and infested soil, the fungus gnats will wreak havoc on the young plants and the rosemary oil provides no soil protection.
- You need to saturate the soil completely for enough of the oil to be absorbed by the plant. You will need a large quantity of SNS 209.
- SNS 209 takes weeks to come to full effect. You will need to watch as the fungus gnats grow stronger while you wait for the plants to absorb the oil.
SNS 209 Rating: 0/10 Save your money, time and patience and keep reading.
GnatNix is made of white rocks that you spread over the surface of the soil. They are made of a sharp volcanic rock similar to diatomaceous earth (D.E.). I have had wonderful success with the GnatNix. When you completely cover the surface of the plants in ½ - 1 inches of the rocks it completely seals off the soil. When the flies try to dig through to get to the soil, the protective coating on their bodies are cut and they rapidly dehydrate. This prevents flies that have hatched in the soil from escaping (killing them) and prevents adults from laying new eggs in the soil. This cuts their life-cycle neatly in two. After a few weeks, the remaining live adults will die and you should see dramatic reduction in the fungus gnat population.
For this to work, all soil need to be protected. The files will find the one plant uncovered (including other houseplants). I will issue the drawbacks to the rocks.
- I do not recommend letting the rocks mix into the soil, especially if you have self-wicking bins. The rocks do not hold moisture so all water will drain right through. This is good for the rocks on top but not great if it gets mixed into your soil. To avoid this, I use my vacuum to remove the rocks from the surface before harvesting or reseeding a bin. I then am able to reuse the rocks from my vacuum to replace on the surface of the soil. This saves rocks and prevents them from being mixed in.
- Roots crops will start at the top of the soil, not the top of the rocks. When growing carrots, there may will be a small section on the top of the carrot that was in the rock layer. This section often looks darker (almost like sun-burnt shoulders of an outdoor carrot), and may have inhibited growth. I sometimes will remove this small section for aesthetics.
GnatNix Rating: 9/10 Kills the flies, minor hassle to deal with harvesting/replanting. (Get it here!)
How can you prevent fungus gnats from starting?
Part of the problem with my propensity for fungus gnats is the self-wicking bin method described here. This means the entire +12” inches of soil are moist all the time. It provides fertile soil for laying eggs. If I used a drip system where the soil was allowed to dry out once in a while I may have less of a problem with fungus gnats. I am working on a new irrigation system, stay tuned.
Yellow Sticky Traps:
These yellow cards found here are cheap and covered in a sticky gel. Fungus gnats get stuck and die, simple as that. These are good for indications of a problem. I try to place fresh cards near my plants, if I see a fly stuck I know I need to address the problem before it flares up. They are good for catching adults, but will not solve the problem. If you get the sticky gel on your fingers, wash with oil first then water as the gel is hydrophobic.
Yellow Sticky Traps Rating: 5/10 Good for monitoring of problem, not solving the problem.
I hope this article prepares you to handle major indoor pests in your growing system. Blue dawn dish soap in water is a good way to kill aphids. Yellow sticky traps are good to let you know there may be a problem with flying insects. GnatNix on the soil is a good way to disrupt the life cycle of fungus gnat. Good luck!
Have you ever had these pests in your house? Have you had other pests, and what worked to get rid of those?
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