They are probably fungus gnats, which for me are harmless but annoying... they like overly wet soil... so try letting it dry out a bit... cinnamon on the soil is supposed to work and maybe one of those sticky yellow strips? If you aren't much into clashing yellow in your decorating anyway. :D

Harmless to mature plants, but not so harmless to young seedlings....The larvae will feed on roots and small seedlings with small root systems can weaken and die.
Heathen is correct about allowing the soil to dry between watering...at least 1/4" down. Also scratch at the surface to bring up eggs which will dessicate. If you have other plants in the house that are overly wet the gnats will seek these out as well.

Vera

I have been wondering about this as well. A couple of my juvenile citrus trees have been having the little gnats around them a couple days after I water them, stirring up the topsoil seemed to get rid of them.

I have these little flies on a couple of pot marjoram seedlings and I'm trying the 'sticky yellow strip' approach placed strategically close by. The soil was rather too moist so I suspect that's why.

I get these also....i tried misting with a mild soap solution to run them off, and it seems to deter them of a while, but they come back....i usually wait to water more mature plants until they actually begin to show signs of wilt, but i have been maintaining a high humidity environment....possible this contributes to problem....in addition to larger plants, i also have seeded pots and cuttings, so it's tricky....a more pesky trouble is little spiders; they seem to have an affinity for marigold, chicory, and butter and eggs....the stupid pests basically suck the plants dry...i plan to try garlic juice in water next to deter them, and failing that, hot sauce in water....

peaceful day,

doug

I grow my seedlings in a soiless medium with a top layer of coarse sand or fine vermiculite and water from the bottom only. This top dressing helps the pots to dry out on the surface quickly. When I start my sowing I always have a fan blowing 24/7. It doesn't have to be a large fan but you need the air circulating. I just brought all my potted stock plants in from outside into the greenhouse and the fans were immediately turned on. This will eliminate many problems.

I had thought when I read your subject line that you had brought mint in from outdoors and the result - - here comes the fungus gnats! That is a problem we face every year when herbs and houseplants are brought in for the Winter. It seems that this is common to a greater or lesser extent with your responders. Doug, you almost for sure have red spider mites.

Herb_lover, what I do is take the potted plants outside on a warm afternoon and spray them with pyrethrum/rotenone - making SURE to wet the soil surface. About week later, the plants & soil is sprayed again. This usually stops all the gnats.

Pyrethrum is a natural insecticide which comes from a chrysanthemum species. You can buy a powder containing 100% dried pyrethrum flowers. Permethrin is a pyrethroid (a synthetic similar to pyrethrum) which remains effective against insects for a longer period of time. Permethrin is used by exterminators against termites and soil dwelling insect larva in lawns. It is used by farmers for critters like cutworms below the soil surface. It's also recommended by U of Connecticut for fungus gnats (see link below).

You can use pyrethrum powder on your dog to control fleas (or for killing aphids in your garden, for that matter). And, I'm thinking that it may be a better way of getting rid of the gnats than a spray. Could be wrong.

Remember, pyrethrum is a poison even tho' organic and not very persistent.

Steve

Here is a link that might be useful: UConn IPM: Fungus Gnats

Reporting back about my sticky yellow tape experiment which appears to have been a success. It kept falling off where I placed it, so I left it lying on the soil surface. A short while later, flies were found on the upperside of the tape. I haven't noticed them elsewhere since, but I don't think I had very many.

Joanne, I have the same problem!!! Only I was stupid enough to plant the mint next to the walk to the front door!!!!

Actual bees come to mine and I don’t mind them, but there’s a mass of very large flies about 1/2 inch long, a fuzzy thorax and a shiny black abdomen. Annoying!!!

For the past several years i have kept the soil of all my houseplants covered in a thin layer (enough so you cannot see any soil) of sand. Presto! No fruit flies at all-not one! It keeps the adults from laying eggs in the soil. I even water from the top. No issues at all. If you are from the Pacific Northwest then thank Sisco Morris for the tip next time you see him!!

So no one seems to know a solution for the flies around the OUTDOOR mint?! Yes they are flies not gnats. I too planted my mint by the front door now I have to use the back door or walk through swarms of flies to access my front door.

Is the mint flowering?

Yes! I found more info on another site. I cut all the flowering shoots off the plants and immediately no more flies!!! hooray! ;)

The insects are attracted by the flowers. Some of us think this is a good thing since insects are in decline all over the world. However, if they are a nuisance clip the blooms off. Also the mint will grow bushier and produce more fresh shoots if you regularly shear them before they flower.

When I was growing cpmm

Use a cloths pin to hold it onto a wood stick.

These are big old flies! I'm having company this week and we are going to eat out there. What can I do to get rid of them? The bees aren't a problem, the flies by the thousands! The mint grows all along my patio. This hasn't happened before.