I feel I had success this year with mine. Started off in modules in March,, IIRC I put three seeds in per module on a 24-drop set, thinned to the best seedling in each module. Planted out mid may from memory. THe secret is rich soil (I put a load of horse manure in and a big shake of BFB for each station) and watering.... the old joke is that as soon as it stops raining get down to the celeriac with a watering can... I just plumbed it into the autowatering in the GH cos it was close so it got two hours per day every day rain or shine....
I'm now harvesting 5-6" roots, they've stood the weather OK and are great roasted. Sort of like a celery-themed parsnip. A lot easier to harvest than a parsnip when the grounds frozen too....
