Why are my seedlings dying

I start off seedlings of Mini Cucumbers in Seed & Cutting compost, in small plastic celled tray.
Transplant into small pots when well germinated ... with as little disruption as possible.
They thrive (as can be seen by pots on the right)
Then leaves fold over, and the plant dies

They are on a North facing window ( I also tried some in Green house by day) ...

The 2 on the left were good healthy plants then died, the 4 on the right are new sowing, and looks like the same is happening again with the middle pot already starting to curl.

Any suggestions

 

Not sure really but all I can offer is that they weren't strong enough to be moved on. They still look small to me but the again I've never grown cucumbers of any variety.

 

The Secrets To Growing Cucumber Plants Successfully In The UK - Vegetable Growing
Any help?

 

Hello Sargan, definitely wait until they've got 2 proper leaves ( apart from the seed leaves) before repotting. Go easy on the watering and keep an eye open for sciarid flies. If you notice tiny black flies flitting round the pots, stick a match head-down in each pot.

 

I'm in the South - no cold here (now snow up North), they are in a warm room, does not drop below 10 C at night - I can put them on a heat mat if you think it worthwhile, have found it makes plants leggy.

 

I agree they have got chilled in the very early stages of growth they need a steady temperature of above 15c and rising to 20c during the day.
Slightly older plants can handle a bit more variation.
I'd sow directly into the pot, saves pricking out.
Also agree that you are really a bit early unless you have a pretty warm green house.
They go leggy because a north window is not really bright enough.

 

Don't intend putting Greenhouse yet .... not until May, thought it worth starting off indoors now.
Obvioulsy wrong

 

You can get away with early sowing of some plants but with cues they grow so fast once things warm up ,and are temperature sensitive in the early stages, it's usually better to wait and watch the weather.

 

A silly question, but what does the match head do and would that work on house plants too? I have over 20 house plants and we get tiny little bugs flying around the house, even in rooms where there are no plants, are these sciarid flies?

 

Why You Should Place Matches In Your Plant Pots - Ask a Prepper.

Hope this helps you @Tinkerbelle61

 

Thanks @Upsydaisy l’ll try this in the house plants and see what happens, it would be so nice to get rid of the little flies.

 

Hello, sorry for the late reply..been busy Yes, they'd be sciarid flies. They breed like...flies....in damp compost. Not sure about the science behind the matches, but guessing it's the sulphur content. Sulphur and flowers of sulphur used to be used as a soil treatment against pests and diseases. I'm sure it will work for all houseplants, you just need to increase the quantity of matches according to the pot size

 

Must buy more matches before they are banned.

 

Thanks @noisette47 for the advice, it’s odd though as the little flies seem to be about more when the compost dries out, I notice the flies and it reminds me that I haven’t watered them lately! I need a better reminder system