leaf curl in young tomato plants

REMF33

Quite a few of my young tomato plants seem to have leaf curl.
I have never had this before, at least not so early on. They have not been outside so I think on balance not a virus (although it could be in the compost, I suppose). Any suggestions? I realize it's a bit lke going to the doctor's and saying you feel tired all the time... 
The only thing I have done differently from usual is to use peat free compost. I am using a moisture monitor so probably not under or over watering. They are in 3 inch pots but some of them are getting quite tall, although nowhere close to being root bound. Might potting them on (maybe into a different brand of compost) benefit them, or could that just shock them too much?
Some have been under grow lights. Others are just near a big window. The temperature has not been excessively hot or dipped below 12C.

The two main varieties afflicted are Shimmer and Big Mama Hybrid. I have read that the latter is prone to leaf curl.
It's a bit distressing!

Fairygirl

They possibly need moving on into bigger pots, but sometimes it's just a case of the foliage outdoing the rest of the plant for a short time, and the moisture isn't quite reaching the leaves fully. If the roots are showing out the bottom, then pot them on and bury them up to the first leaves. It shouldn't set them back enormously -  it's quite common. 
Do you have a pic? 

Even on a sunny day that isn't too hot, they can get a bit frazzled on a windowsill too. If that happens with mine, I close the blinds. In that warm March we had, my south east facing kitchen was reaching temps in the 30s, which is far too hot for any young plant. 

REMF33

Thanks. I will pot them on, then. They are a bit leggy, I suppose. I know the pots look ridiculously small, but the roots are not yet visible. I need to start off later next year. (As I probably said elsewhere, I stupidly thought I'd be able to put them in the (new) greenhouse earlier than I could put them outside i.e. around now, so I started them off earlier than usual. Doh.)

Fairygirl

Oh - those are very big for the size of pot!
I think they'd appreciate a bit more room 
I'm surprised you aren't seeing any roots come through the drainage holes though. Perhaps they're going round and round instead. 

REMF33

I think I have just one a bit wrong, generally, somehow this year! Or maybe I am doing myself a disservice. I have plenty of other healthy tomato plants (but now wondering if I should really have given half of them away on Sunday!)

I don't think the roots are going round and round. I gently pulled one plant out of it's pot to have a look. I will pot them on anyway tomorrow. Tomato plants do usually seem quite tolerant to a little root-boundness for a limited amount of time, though, in my experience.

I am wondering if I am not getting the watering right in spite of all my monitoring. I suppose being in small pots will effect that potentially. Peatless problem too (not used to it yet, nor this brand...)

REMF33

Ha I couldn't wait. I just potted on 4 of the saddest-looking ones. They weren't root bound, really. I have used a different potting compost.
Will do as many of the rest of my larger tomato plants, curly leaves or not, as I can tomorrow. (I don't really have enough of the right sized pots, alas. I don't really want to put them in much bigger ones if I can help it.)

Fairygirl

Yes - I like to stress mine a little, but maybe they're just top heavy due to the circumstances. If it's been warm where you have them, they'll have shot up, and that would suggest the lack of water reaching all the foliage, and hence the curling. 

I know what you men about the peat free stuff too. I've experimented, using my recently sown sweet peas. Most have been doing as well as the ones in a standard mix, but there's one variety which hasn't appeared yet. They've all had the same care, and watering according to how they're doing, and I've not noticed a massive difference re moisture loss with the ones in the peat free .

These things sometimes just happen, no matter what you do! 

REMF33

I am not feeling that optimistic. Just noticed one in a slightly bigger pot has the same problem...   Will just have to wait and see. If all else fails, there are bog standard varieties in garden centres and I have a few on order from Suttons.
I just hope the ones I gave away are ok in the end.
I do feel a little off kilter with my growing this year, but there have been distractions...

Fairygirl

It's tricky if you're using a different compost, especially if you haven't done a comparison sowing with the one you normally use. Some of these peat free ones seem to be dreadful, judging by comments on the forum.
If you've used a different compost, maybe they'll perk up and be fine in a couple of weeks. 

REMF33

I hope so. I confess I don't quite trust peat free. I had some peaty stuff left over and will use that for potting on. I think my peas were sown in PF and are ok, though... All the other flowers that have been pricked out into it so far, seem ok too.  Everything was originally sown in PF seed compost, but a different brand. (I really like the seed compost, actually. It's the Fertile Fiber one.)

REMF33

So I potted the whole lot on in new compost. Some of the plants were far too wet (not pushing the hygrometer down enough, clearly.) A few were a bit pot bound but these were actually among the most healthy specimens. The ones I potted on last night still looking very sad, so maybe beyond help, but that's only four plants and I think I have other ones of each type.
So, I still don't know what the problem is but I just hope that a change of compost will help. (I still have lingering in my mind the worrying possiblity of herbicide-contaminated compost.)
Some Cosmos that were looking unhappy were a bit soggy too...

I am not going to water anything for a few days! (Which is awkward because in a few days I will be away...)