How to Prevent and Kill Microgreen Pests Episode 23 of the Microgreens Podcast

Microgreen Pests

Episode 023 of the Microgreens Podcast

There are few microgreen pests to worry about. Because microgreens are usually grown inside the house, and they have a short life span there isn’t much contact or time for infestation.

The three most common pests are aphids, whiteflies, and fungus gnats. 

In this episode of the Microgreens Podcast, we discuss how to prevent microgreen pests from infesting our trays; and when they do, how we kill those little pests. 

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Here is a Related Article

We have published a related article on How to Stop Fungus Gnats from Attacking Your Microgreens.

Links to Products Discussed in the Podcast

Diatomaceous Earth

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FREE Home Microgreens Grow course that teaches you the basics of growing microgreens in your home! There are 12 video lessons (over 120 minutes), downloads, and more written information and tips!

Yellow Sticky Traps

Home Microgreens Potting Mix

microgreen soil

Below is a Transcript of the Microgreen Pests Microgreens Podcast – Episode 023

Welcome to the Microgreens Podcast, episode number 23.

Today, we’re going to talk about insects that bother your microgreens or can bother your microgreens.

We’re not talking about microgreens that you may grow outside or on a patio. We’re going to talk about the ones that are in your house, either on microgreen racks or near windows.

There are really just three that are very common to microgreens.

These are aphids, whiteflies, and fungus gnats.

Now whiteflies generally are around your house plants. They like to lay their eggs on the undersides of larger leaves. So they don’t really bother microgreens. They may be around your microgreens if they’re around other house plants and we’re going to take care of them in the same way that we take care of fungus gnats.

So we’ll discuss those later.

The other pest is aphids. The only time I’ve had aphids on my microgreens is when trays of them have been by the windows in the summertime.

And they generally don’t get on the microgreens that you harvest in 10 or 14 days.

But the longer term, microgreens like basil and cilantro, especially basil and cilantro, and if you have some holes in your screens they can cause an infestation of those longer term microgreens.

There really is a problem with microgreens at that point, because they’re really hard to get off the plant.

You could have put insecticidal soap on them.

I don’t really think that’s a great idea.

I mean, it’s really hard to wash insecticidal soap, whether it’s harmless or not, off the microgreen. Still will get that taste.

Aphids are really hard to rinse off your microgreens after you harvest them too.

So if you do get aphids and again, really the only way you’re going to get aphids, if they’re on other house plants, you bring them into the house or from other house plants and the microgreens are by a open window. That’s when you could get aphids and I’ve only had them once or twice.

What happened is that I actually had some basil plants growing in these large pots, underneath the windows. My microgreen trays were nearby. I think the aphids infested the larger basil plants and then spread to the other microgreens.

So really it’s a good idea to keep your microgreens away from your other house plants or other indoor growing vegetables that you may have.

With larger leaf basil, it’s pretty easy to get the aphids off before you eat it, microgreens, it’s a little bit harder.

Aphids are tough and the best prevention is just to keep your microgreens away from house plants or large growing herbs that are in the house.

Aphids however aren’t that common.

The most common insect that bothers microgreens is fungus gnats.

And again, those can get into the house either through a window screen.

They’re pretty ubiquitous. They’re almost everywhere. They just show up.

Bags of potting soils can also contain fungus gnat larvae or eggs.

We’ll talk about this in a little bit, but fungus gnats are a little bit easier to take care of and to get off your microgreens.

But really the best way to deal with fungus gnats is prevention.

So let’s talk about these preventive measures first.

Fungus gnats can either come in on the plants or in the soil of any plant that you bring into the house. So if you bring a plant home from a nursery, a garden center, or a box store, it’s a good idea to stand around those plants beforehand.

Just sort of be quiet and see if you notice any insects flying around these plants. Fungus gnats are really small black flies.

Get a little bit of light behind the plants so that you can see through and if there’s anything flying, you will see them.

If you see any flying insects around the tropical plant center or the garden center, don’t buy those plants.

It’s just a safe bet not to bring any plants into the home that have been infested by fungus gnats.

If you do have to have that plant, that’s a special plant that you want and you bring it home, try to quarantine it, try to put it in someplace where it’s not near your other plants, where if any flies get off of that plant or any larvae hatch out of the soil, they won’t get to your microgreens or other house plants.

Having a quarantine space is a good idea, really anytime you bring home any tropical or house plant from a garden center or a box store, especially the box stores, those plants are just watered over the top.

The soil is always moist and that’s what attracts fungus gnats.

Fungus gnats need wet moist soil in order to lay their eggs.

They’re attracted to wet moist soils and damp organic matter. And this is especially true if the soil has some dead leaves laying on top of it, where the flies can get underneath there. Those leaves will hold moisture onto the soil and the fungus gnats will lay their eggs.

The fungus gnat eggs take between 10 and 14 days to hatch.

So there’s a long incubation period there.

Fungus gnats actually live in the soil as larvae and the larvae will feed on the roots.

I forget how long it is before they pupate and turn into flying fungus gnats. But I believe it’s quite a long period of time.

The worst case is those eggs, if the soil does dry up, those eggs can lay dormant for a long time.

So the best cure for fungus gnats is preventative.

Do not have moist soil.

We’re talking even with house plants. If you can get by without top watering your house plants, that’s a great thing.

Keep the surface of that soil at least semi-dry and you won’t have any problems with fungus gnats.

They’re really drawn to over moist soil.

But as I said, fungus gnats take a long time for the eggs to incubate and they also can lay dormant. And a lot of times you can bring in fungus gnats from potting soil, even a so-called sterile potting soil that you find in your garden center.

This is because the bags that the garden soil is stored in actually have holes in them. And these holes are a dual purpose. One, they’ll let out any excess moisture because these bags are stored in cold places and warm places.

So moisture will condensate on the bag. So they do need the holes for the moisture, the extra moisture to come out of the potting soil bag. The bags also have these holes so that if there’s a change in air pressure, so if they go from a low altitude to high altitude or high altitude to low altitude, the bags don’t expand or heat up and expand with some air. And an employee or customer drops the bag, or stacks up a bunch of other potting soil bags on top of it and that extra air can actually burst the bag like a balloon, it blow out a seam.

So they have holes in those bags so that when you put weight on top of the soil, it can compress. The air will come out of the bag and won’t blow the bag open.

However, those holes do leave room for fungus gnats to invade and lay their eggs in the soil.

And then you bring that soil home, you put water onto it, you plant your microgreens and then you have a fungus gnat infestation.

So I recommend not to buy any potting soils from garden centers, nurseries, or box stores in areas where the soil is stocked or stored near the house plants or the tropical plants.

That’s just asking for trouble and sooner or later you’ll be buying a bag of soil that has fungus gnats in it.

Now there are precautions and actually, the Home Microgreens potting mix has these precautions, one of the cures, and we’re going to talk a little bit more about this later, to help get rid of fungus gnats in the soil is called diatomaceous earth or DE.

It’s basically a silica skeleton of a diatom. That’s what diatomaceous earth is. It’s also used for filters in swimming pools. It’s very small and it’s actually a silica.

It’s basically just like quartz, if you will. And it’s very sharp, with lots of shards.

What happens is the larvae crawl through this diatomaceous earth, even just a little, it’s so sharp that it actually cuts the exoskeleton of the larvae or even the female fungus gnats as they’re laying their eggs.

Those cuts will actually desiccate the moisture out of the larvae and out of the fly and kill either the larvae or the flies.

It’s basically death by 10,000 cuts.

Home Microgreens potting mix actually has diatomaceous earth in it.

So there’s a little bit of a precaution.

I don’t know of any of the other commercial brands that do this.

I have never had any problems with fungus gnats with anything I’ve grown, but then I’ve been really careful to take all my house plants out of any areas where I grow microgreens, to begin with.

As a matter of fact, I did get rid of all my house plants because I have so many vegetable garden plants and microgreens growing that I don’t really need to take care of any other house plants.

That is the first cure.

Our preventative measure is not to overwater. Don’t water over the top. Don’t keep the surface of that soil moist.

The second precaution can be to add a little bit of diatomaceous earth, it’s fairly inexpensive, to the tops of your soil or mixes it in with your potting soils. That way if there are fungus gnats, the larvae will have a tough time getting to the roots, grow and turn into other flying fungus gnats.

If you see some fungus gnats, it’s not a bad idea to sprinkle a little bit of diatomaceous earth on top of your soil or add it to the soils of the next microgreens you’re going to plant as a precaution.

So diatomaceous earth is really a very good product to have in the house.

It’s going to last forever. It’s fairly inexpensive and it’s handy for a lot of those soil-borne insect problems. You can also obviously use it in the garden. It’s pretty much all I do use in the garden. I’ve tried a whole bunch of other things. And to me, diatomaceous earth is one of the best measures against burrowing insects.

I do want to say that all the cures that we have for the fungus gnats will also kill beneficial insects.

So it’s not something that you want to haphazardly put into anything in the garden where there could be beneficial insects.

We don’t want to kill those.

Only add it once you see a problem insect.

There are two other physical methods that take care of fungus gnats. The first is a vacuum cleaner. Fungus gnats are small, very tiny flying insects.

So if you do see them flying around your plants, use your vacuum cleaner hose. Don’t suck up the plants, but just use the vacuum cleaner hose around the plants.

Any of them that are flying will be sucked into the vacuum cleaner and killed. Also, take your trays or your plants and shake them, drop them so that if there are any fungus gnats on those plants, they’ll fly up out of the air and the vacuum cleaner can take care of them.

Another passive way to do this is to use yellow sticky traps. They’re just basically a piece of hard cardboard, solid cardboard, not corrugated, but solid cardboard that has a sticky glue on it. They’re gently yellow because the yellow color attracts the insects. And it’s just a physical means. So the flying fungus gnat flies onto them and sticks and can’t get away.

You would have to leave these around for probably a month or so to make sure that all the fungus gnats eggs in your soil, the larvae have hatched and gone into the flying stage so that they can get caught into these sticky traps.

 So I think that pretty much covers it.

Let’s do a little summary here.

So there are three insects that are commonly found on microgreens or most commonly found on microgreens. These are aphids, whiteflies, and fungus gnats.

Aphids are pretty tough. If you get them, can try to clean them off, rinse them off, but it’s a very difficult job.

And generally, you’re better off when you see them just getting rid of that tray, so the aphids don’t spread to other plants.

The other two, whiteflies and fungus gnats we can take care of the same way. Whiteflies do lay their eggs under the underside of leaves. So they very rarely are laying the leaves on microgreens, generally are on some other larger house plant that’s around the microgreens.

But again, the sticky traps, and the vacuums will take care of them.

The diatomaceous earth won’t work so well because they don’t really enter into the soil.

For fungus gnats, the best prevention is to not buy soil that is stored or stocked anywhere near house plants or tropical plants in the garden center or box store.

Second, keep your soils covered.

Third, bottom water. Don’t keep the surface of the soil moist at all. If you don’t have moisture on the soil surface fungus gnats won’t be a problem.

If you do have fungus gnats, get out your vacuum cleaner, take the hose end off, and tap your plants. Let those fungus gnats get flying and suck those babies right out of the sky. That will kill them.

However, you probably still have larvae in the soil. So either you’re going to have to put diatomaceous earth on the soil or purchase some yellow sticky traps.

Put these sticky traps up, leave them up for about a month, even on other places, other soils where you don’t think there are fungus gnats, they may have larvae or eggs in them. So keep the sticky traps there. Soon as those larvae hatch, they’ll be attracted to the yellow sticky traps, and you’ll get rid of the problem.

It’s not very often that you have to worry about insects on your microgreens in the home, but if you do, it can be rather frustrating.

So it’s a good idea to have some diatomaceous earth or yellow sticky traps handy, both will last forever. Then they’ll be handy when you do get an insect issue with your microgreens.

I hope you have a great day.

And I hope you plant some seeds today and get those healthy nutritious microgreens growing in your home.


  • Todd

    Todd is the founder of Home Microgreens & the Home Microgreens store. He also writes for several other websites, including MyViewFromTheWoods.com. Todd worked at a large farm market, garden & nursery center for 20 years. Somehow he snuck off to become a geologist and professor before coming back to his senses to write & lecture about microgreens and gardening. When not at the computer, he can be found in the garden, trout stream, or mountain trail with his new Springer Spaniel Caden.

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