Seedlings stopped growing…

[Sailingby]

Is anyone else finding that their seedlings have stopped growing for 4 weeks? Rudbekia (Goldsturm and marmalade) and echinacea (Magnus and white swan) have been the worst - (stopped after the first 2 or 4 leaves) - but salvia (red blaze) and cosmos also doing poorly. I’d put them outside - but covered with plastic lid when raining - soil surface is going green with algae. I’ve brought them inside at night the last 4 days when it’s been cold (London) and to stand a chance of drying the compost out a bit. Roots not really developing. Did try some much diluted feed as some of the leaves looked a bit yellow.

I was going to say that it's been really cold, my bin (midlands) had frost on it at 4am the other morning.

Did you start indoors then harden (not sure of correct term) them.

They might have been killed off, the temperature has definitely fallen to zero or below.

Sorry that's not much help.

Yes - I started off indoors - until they got the first 2-4 leaves - and were clearly flourishing. Once outside I covered them with a plastic lid overnight. The last few nights I’ve brought them indoors. Daytime I’ve been putting them where they get the most sun outside… It’s bizarre - my sweet peas have done really well (I planted them in the garden 4 weeks ago).

It's been cold and quite dark here for the last week, I've kept mine inside.

Sweet peas are hardy, you can sow them in autumn and leave them out all winter! All the others you mentioned are more cold sensitive and Cosmos is particularly tender. It'll be the cold.

my outdoor plants have all stalled the last couple of weeks due to the cold weather. they will pick up now with the heatwave that's in the forecast.

Some of my seedlings are looking very pathetic at the moment. It’s been so cold. The recent frosts damaged the potato plants on the allotment.
Hopefully some warmth is coming.

Unless you are on the south coast - 10 days ago it was boiling hot in the day/frosty at night. That’s too much for tenders to cope with. Unless you have a heated greenhouse they’ll be in shock. The same has happened to my tomatoes/cucumbers.
So, now you’ve had them in pots longer than ideal, they’ll have used the nutrients up. They’ll recover when the weather stabilises, but going forward don’t be so keen to sow, it’s all a lot easier if you wait a bit and (hopefully!) have the weather on your side. Give them a weak feed if you've got some fert to hand.

I’m in London - the temperature hasn’t gone below 6 degrees at night - which I appreciate is a bit cold - but 6+ trays of seedlings start to take over a small house! I didn’t sow them until the first week of March - which I thought was quite cautious! Do you think the warmth indoors now will help them recover - plus diluted feed? And warmth from tomorrow onwards…?

The warm sunshine during the day then low temperatures at night is a recipe for repeatedly shocking your seedlings.

I'm in the West Country and haven't put any of my seedlings outside yet because the night time temperatures are too low and the days haven't been much better.

If I were you I'd just put the whole lot somewhere inside and let them relax a bit. I wouldn't feed them....you might make too much soft leafy growth too early on.

In my experience all seeds go through a stage where you think they've stopped growing when actually what they're doing is concentrating on putting down roots to support growth. Keep the temperature consistent and let them do their own thing in their own good time.

I got the hardening off completely wrong. Left tomato plants out when it was too cold and was too windy for the courgettes. Everything has died!

I think they are just growing their roots and probably more slowly than they would normally. I keep checking the bottom of pots for signs that they are filling out the pots and they aren't really. I'm hoping a bit of warmth next week will send everything skywards. In the north west and while we've had some sun it's been cold with a cold wind. Still got the heating on...

Have you got somewhere for a small cold frame? They’re very helpful for hardening off. Even a pane of glass resting against a wall would help. Well propped up so the wind can’t get under it obvs!

I haven’t got room for a cold frame - but I do cover them (unless very hot) with tall plastic covers - with the vents open - again - when the weather is mild I take them off to allow air to circulate.
Clearly this year I have got it wrong - just trying to see how I can make the best of it. 8 trays currently enjoying the warmth of being indoors for the 6th day.
it hasn’t been that hot during the daytime - I thought putting them out in the morning sun (before it started to rain) would be the right thing to do..

I have everything inside still and they are growing painfully slowly.

I’ve given the tomatoes especially a liquid seaweed feed and some have grown a bit more.

hopefully the predicted good weather will bring things on.

My runner beans were growing 6 inches a day indoors. I planted them out a week ago and they haven't grown at all since. Hoping the warm weather later this week kicks them off again.

Mine have largely stopped growing too- I've been putting it down to the fact they so badly want out of their little pots but it's been too cold to plant them out (also London). I'm hoping that with the warmer weather later this week the time will finally come to plant them out in much bigger pots and the growth will come back. Hopefully yours will be the same!

I agree with this. And love the phrase 'let them relax a bit'!
OP it was a learning curve for me too as I was focused on frost only, but lots of things don't die between 5-10 degrees bit just stop growing and stay small, which means they don't take up much water, then they just sit there sulking. I've put things out yesterday as the night temps are forecast to be 10+ but would definitely let yours relax and get less soggy. And the echinacea and rudbeckia are perennials anyway so even if you don't get many flowers this year you'll hopefully have lovely strong plants that will romp away next year!

YES. Everything slow. And now that good weather is forecast finally, I’m going away for the long weekend and they may all shrivel up! I can’t decide whether it’s better to get them all outside and risk them frying without enough water, or keep them in and risk them not getting the sunny boost they need.

Thanks for the tips and empathy. I’ve now looked at the forecast for the next week - and wondering how to acclimatise the seedlings to 28 degrees…! Will the algae on the surface grow faster than the seedlings?! Should I repot them into new compost… or watch them like a hawk in case they show signs of collapse!!

You could repot, but as @FoulBlister said don't go mad with the feed. Keep them in the shade and 28 degrees shouldn't be a problem.

Mibe too. Hoping some warm weather will kick start them and can finally plant out veg plants.

This year has been very difficult, and I agree with PPs I think it's the cold.

I have found germination very hit and miss and the seeds that do germinate take an age to get going. I have got loads of stuff on window sills I don't dare put out yet

The joy of gardening

Are you using peat free compost? I do but find the quality varies wildly - a couple of years ago I had similar to you and I think it was due to a dud bag - everything started off well then stalled and no amount of feeding would help. If they're big enough to try in some new compost, maybe A/B test and pot on a few then see how they compare after a week? You can also top dress and put fresh compost on top if the existing algae stuff has settled lower? I've had success with the sylvagrow this year but I think the new peat free brands can really vary wildly!