No worries Cara, glad to pass on what little knowledge I have. Your post was timely actually - reminded me I hadn't put any in yet!! (We're a bit behind thanks to all the soggy weather this winter.) Celeriac don't like being disturbed, though equally better brought on in modules/pots to start with (see , they even start off awkward!). Just disturb the roots as little as possible when you transplant them. Try creating a shallow dip in the soil when you transplant them to act as a water sink when feeding/watering - it helps somewhat. If you can get the feed/water routine right they should do great in a polytunnel.
I can think of worse things than being seed sowing happy, especially as there's a 'happy' in there
I'd love to hear how you get on with the celeriac again if you remember come harvest time - I've only ever grown them outdoors, which is not ideal (though it does work), and at this rate won't have the planned polytunnel in place come time to put them in the ground this season...
Good luck - I'm off to plant more seeds... Is there such a thing as too many...?!?