Seedling Flies

francesmckeon21

Hello, is anyone able to help me, please?  I have grown geraniums, sweet peas and achillea from seeds. I'm thrilled with their progress ( yip, it's all new to me 😊), however, I have many tiny, black flies both on the seedlings and on the compost.  I've googled the problem and it was suggested I use hydrogen peroxide 1/4 parts on the plants. Has anyone any other less drastic-sounding advice? I'm frightened the solution will kill the tender plants. 
Many thanks
Frances

MikeOxgreen

Normal fly spray will do.

GardenerSuze

They could be fungus gnats which can be the result of overwatering. Hydrogen peroxide sounds drastic. I guess you have tried soapy water not sure of the ratios.

francesmckeon21

Thank you both. I haven't tried either suggestion. 

Fairygirl

Where are you growing them @francesmckeon21? Are they indoors, and what size are they?

bédé

Sounds like fungus gnats.  Try some of those yellow sticky pads.  

bédé

I haven't heard of hydrogen peroxide.  Worth a try.  What concentration does one start at?  If 6%, then 1/4 is quite weak.

One thing about H202is that it becomes water and oxygen.  Both quite harmless at low concentrations. 

H202 is the active ingredient from fermenting barley straw added to ponds to control algae.

Fairygirl

Water -and/or a hand, usually works perfectly well, as @GardenerSuze says, or putting plants in a cooler site, hence my question 

francesmckeon21

Fairygirl said:

Water -and/or a hand, usually works perfectly well, as @GardenerSuze says, or putting plants in a cooler site, hence my question 

Thanks. They are on a heat mat at the moment so probably nice and toasties for the wee gnats. The flies/gnats are tiny and very flighty. 
Thanks very much for your help, I'll spray some soapy water on the seedlings. 

francesmckeon21

Fairygirl said:

Where are you growing them @francesmckeon21? Are they indoors, and what size are they?

They are indoors at the moment. The sweet peas have started to germinate so reading advice on GW forum, I've put them in an unheated greenhouse.  
Should I also put the geraniums and achillea outside? The geraniums have only 2 leaves each at the moment. I have a heated greenhouse too.
Your advice is always welcome, thanks.

Fairygirl

Ah - this is the problem. Heat and moisture is a perfect set of conditions for those compost gnats. 
There's no advantage to using heat for sweet peas, apart from a bit of natural warmth in late winter/early spring when sowing indoors. They make better plants if they take around two or three weeks to germinate, and they need no heat to do that. This is why it's not a good time of year to sow them either, certainly not up here, or anywhere colder. Around mid March is ideal, as they germinate slowly, and are at a decent size to then go outside when the weather is more reliable.  
Otherwise, you just have to spend time checking them, and hoping they don't succumb to cold weather, which can happen very easily in the next couple of months, or, you have to keep them heated and pinching them out long term.
If they've just germinated, you may have to do that, or else hope they continue to grow well enough in the unheated greenhouse. I'm not sure which will be better, so you may have to experiment. Not something I've ever done. If they're only an inch or two high, that's far too small to suddenly go outside, even in a greenhouse. 
Too much heat leads to weaker, etiolated plants, generally, and then it's hard to acclimatise them for outdoors.  Lack of light here is also a problem at this time of year.
In warmer parts of the country, it's easier to get them outside earlier in the year, so it's less of a problem. They're very tough and only need protection from the worst of the winter weather, but that's ok if they've been autumn sown, and are sturdy little plants already   

Two leaves on any plant are only the seed leaves, so those will still need some warmth - you couldn't put them outside now if they've been inside, and are only just sprouting.
Geraniums [I'm assuming they aren't pelargoniums?] and Achilleas are hardy, so would have been better sown either a bit later [or else  in autumn ] without excess heat, but you'll have to keep them inside now, and then move to your heated g'house [probably] for a while before acclimatising them. 
If you have plenty of seed, do some more in a couple of months