Seedlings stuck at cotyledon stage

andrew.g.dallastBmRvLpF · April 2023

Hello all,
I have several sets of seedlings that germinated well but have been stuck for ages at the cotyledon stage - no true leaves. The worst offenders are gaura, penstemon, nicotiana and lobelia. Germinated on a heat mat. Then in a South facing window or green house. Two different types of seed compost used.
Three photo is lobelia, with cosmos sown over a week after for comparison (in the same levington seedling compost)

Any advice on what I should do would be much appreciated!
Kind regards
Andrew Dallas
Inverness

JAC51 · April 2023

I don’t know what the problem is but I have it too 🤨

Lyn · April 2023

Lobelia take a long while to grow, just leave them, they’ll sort themselves out, don’t pick them, hopefully be big enough to plant out in June.

Fairygirl · April 2023

It's still very early for tiny seedlings, but they'll come on when conditions are more suitable for them.

It's often a problem when sowing too early as well. It just isn't suitable for many plants - light can be a big factor when sowing early.
Some composts are a bit dodgy too, and stay too wet, or don't get wet enough, which doesn't help. I'm no longer using them - I use old compost/soil and grit or Perlite, as most seed needs very little to germinate and grow. The only advantage of using new compost at this time of year is that there's more nutrition in fresh compost, which you want to avoid when sowing in autumn, but is good for spring sowing. Easily sorted by adding a little when potting on.

Palustris · April 2023

Not had it this year, but I tried growing some Gentiana verna from seed two years ago. It was still without true leaves 12 months later when I gave up and composted the seed tray. I would love to know why it happens. I did ask a really knowledgible nurseryman and he had no answer to it.

JennyJ · April 2023

I agree, lobelia, nicotiana and some other things with tiny seeds take a while to get going.

My theory is that there's not much energy in those teeny tiny seeds, and the tiny cotyledons don't gather very much light (small surface area) so they're bound to be slower than something like a cosmos or a courgette that has a much bigger seed and bigger cotyledons right from the off.

Lyn · April 2023

With lobelia seeds, you don’t cover them with compost, just press in and leave.

Fairygirl · April 2023

I think there's also the element of chance with many seeds. You can sow an entire tray or pot, all the same seed, all the same soil mix, all done correctly, and some won't germinate no matter what.
It's the same in the wild - not all of them germinate, which is why many wild plants produce so much seed. Many simply don't make it for various reasons, although it's more hit and miss than a controlled environment.

LunarSea · April 2023

I've had the same problem with Gaura but one came good in the end and, though still small, is now in the ground. My Thalictrums have been very slow too.

Obelixx · April 2023

I have this problem with some musk strawberries - sown weeks ago in the same conditions and compost as chillies and tomatoes which are now several inches high and have been potted on twice after being moved from heat mats indoors to the better light in the polytunnel.

Musk strawberries have germinated well but now just sit there. I'll wait a while longer before giving up on them.

GardenerSuze · April 2023

@Palustris I recall watching Beechgrove Garden on TV a long time ago. They grew Gentians from seed and they did point out that they are very very slow.

Seedlings stuck at cotyledon stage

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