When using organic soil indoors, you will inevitably run into fungus gnats and possibly root aphids. Wet soil full of organic matter will almost always end with a fungus gnat infestation. It's as if you are purposely starting a fungus gnat buffet.
A few gnats won't hurt anything, but if the numbers get to high you will see damage to your plants. If it gets even more out of control your plants may even die.
In contrast, any amount of root aphids is bad. Once they take hold in your garden, they are extremely difficult to kill completely. Typically once your plants are showing signs of stress, damage, or strange growth, it's to late.
With both fungus gnats and root aphids it's always better to be preventative. Offense is way easier than defense in this situation. I have seen entire crops wiped out because the grower didn't notice that root aphids had taken hold of their soil. Once you get root aphids, it's a bitch to get rid of them. You will end up spending tons of money, and could lose part or all of your crop.
This is where nematodes come into play. Nematodes are a microscopic worm like creature that will attack the larvae of other insects. If you choose the correct strain of nematode, they will help defend your garden against these invaders.
Steinernema Feltiae Neamtodes is the strain best suited for indoor gardens. This particular nematode will battle a host of pests including:
Beet Armyworm, Black Cutworm, Cabbage Maggot, Codling Moth, Corn Earworm, Crane Flies, Cucumber Beetle, Fruit Flies (Drasophylla), Fungus Gnats (Bradysia impatiens), Onion Maggots, Raspberry Crown Borer, Root Maggots, Sclarids, Shore Flies, Subterranean Termites, Sweet Potato Weevil, Thrips (Franklinothrips sp), Ticks, Tobacco Cutworm & Root Aphids
(Nematode Cluster Coming to Life)
When using them indoors these nematodes are of interest because of their ability to protect you against fungus gnats and rot aphids. Once you apply the nematodes to the soil they locate pests and enter through various body openings or through the body wall. Once they have entered the host pest they inject a bacteria into the pests blood. Nematodes release this bacteria to create food and a friendly environment for their reproduction. As food begins to run out inside the host pest, the nematodes will move onto a new host. The nematodes will continue to do this until they have exhausted their food source.
That's all super sciency & great, but how do I actually use nematodes in the real world?
I have been using nematodes for over 10 years now. I use to use them way more than I needed. I was throwing tons of money out of the window by over applying. What I have found works the best in my indoor gardens is to apply nematodes once every cycle.
I will apply them in my flower containers, as well as mom's and veg containers. When applied outdoors in the right conditions nematodes will last roughly 18 months. Indoors is a different story. I have found that 3 months (which is roughly a flower cycle) is the best time to reapply. In the early years I was using them every month. That's just to much, and a total waste of money. If your garden is on point you may be able to get away with every 6 months, but why risk it for a few bucks. If you end up with root aphids it's going to cost you way more than the extra nematodes would have.
(Nematodes Under A Microscope)
When applying nematodes You want to mix them in room temperature water, and let them sit for about 30 minutes. I will store them 2 or 3 times during this 30 minutes. What's cool is that if you scope the nematodes in the water when you first mix them you will see they are still dormant from being refrigerated. After about 5 minutes under a scope you will start to see signs of life, and it will rapidly progress as you reach the 30 minute mark. At 30 minutes of soaking you should see tons of alive and squirming nematodes.
You want to pay attention when watering in your nematodes. They tend to stay in the same place you put them. So if you are in a rush and miss a big chunk of soil, then in all likelihood that soil will never have a nematode in it. This will leave you vulnerable to attack by pests. I tend to apply them when lights are getting ready to go out to allow them some time to settle in without those giant fucking beams of light roasting them. Gotta take care of your homies so they take care of you right? ;)
Using nematodes with a couple of other preventative measures can really help to keep your soil pest free. The number one thing I would say to use with nematodes is a fabric container. Fabric containers (like Smartpots etc..) act as a mechanical barrier so pests can not enter your soil. This leaves the top of the soil as the only place for pest infiltration.
Since you only need to worry about the top few inches of soil, then the use of nematodes, rove beetles, and hypoaspis miles, along with a weekly application of gnatrol, will keep you pest free. I haven't seen a gnat in my garden in over 1.5 years. Literally not 1 single gnat. As you scale up this can all be applied to whatever size grow you have.
If you want to learn how to grow your own Rove Beetles, this past blog post I wrote about making a DIY Rove Beetle Farm may be of interest.
Years ago it was said by many a grower that gnats are just part of using organic soil indoors. We now know that gnats and root aphids do not have to be any part of your garden, and with the application of nematodes coupled with a few other methods you can garden pest free from here until eternity.