Nicotiania help

I’ve managed to get my Nicotiania seeds to germinate but they’ve just stopped growing. They are currently tiny and have been so for a couple of weeks. They are in seed trays and I’ve had them on a heat mat while it was cool but removed the cover now it’s warming up. They are in a sunny and warm (when the suns out) conservatory. Any suggestions on what I’m doing wrong?

 

I find lots of tiny seeds seem to stall after germination, I'd be inclined to carry on with what you're doing, be careful they don't dry out and water from the bottom, mind the sun doesn't scorch them ,so not too bright, the sun is getting stronger now.
What compost are they in, I'm finding lots of my seedlings are very yellow in the peat free stuff.

 

You're probably not doing anything wrong.
As long as the seedlings look healthy and they're not getting leggy just let them have more time.
It sounds like the conditions you have them in are ok.

But, does it get cold at night in the conservatory?
If it does, they won't like that - I'd put them back on the heat mat overnight

 

I’ve had the heat mat on 24/7. I accidentally bought compost which does contain peat so they are in that but I’m not a fan of this brand so far. Some have done really well eg cosmos other terribly eg aquilegia.

I used the milk carton method with a different variety of Nicotiania where the seeds came inside green balls of something on the same compost and they are doing much better and are bigger I spite of being planted later.

 

Mine often germinate then sit and think about growing for while, I just leave them to get on with it. I presume they are busy growing roots and will start growing more when they are ready.
The green balls sounds like a pelleted form of seed, makes handling small seed easier and you can sow into modules easily for plugs.
How do you get the seedlings out of the milk carton, through the neck with chopsticks?

 

I usually give seedlings a weak dilute of liquid feed if they seem to be stalling and it's too soon to pot them on.

 

The pellets contain fertilizer suitable for seedlings, so that has probably given them a boost.
I often grow N Sylvestris and also find they are slow starters, but once the warmer weather arrives they shoot up to 6ft in a few months.
Just give them more time and don't try and force growth - they'll grow when they're ready.

My only concern using a milk carton is that if there any traces of fat remaining, that may hinder growth.

 

I had that happen last year and gave up on them in the end. Wasn't going to try again but saw a cheap pack in Asda and thought, just one more go. Did a couple of things differently: sowed as thinly as possible (very difficult with those little seeds) and took them off the heat as soon as they appeared. They have been on a south facing windowsill for two or three weeks now, developed their first set of real leaves and I have pricked out the best of them. So looks like I might actually get some plants this year, if I can keep these tiny seedlings alive.

Another thing different from last year is the compost. I always used the coir based compressed blocks for convenience, but this year I bought the "Mr Fothergills" brand enriched seed compost from B&M. It has added seaweed and B&M have it at £4.99 for a 10 litre block with a 3 for 2 offer. All my seedlings have done well in it so far.

 

Thanks all. I’ll continue as I am.

 

Seaweed extract added to all watering of seeds 10ml per 5litres (2 teaspoons per gallon)

 

Can't say I've ever heard of growing seeds in a milk carton.
Do you cut the top off first.

 

Some people use it to get a head start early in the year. Lots of YouTube vids on it. It’s basically just a mini free propagator. Cut round on 3 sides and then tape it down once seeds have been sown. It works really well.