Maxim
Celeriac in the US

Celeriac seeds are tiny, like dust almost, so don't bury them deep. I like to sow mine indoors in seed trays, just sprinkling them on top of moist compost and lightly covering with a dusting of vermiculite, or even just leaving them exposed. They need warmth to get going, around 60-70°F (15-21°C) is ideal, so a warm windowsill or a heated propagator is your friend here. Timing depends on your USDA zone, you know what I mean. If you're in a colder spot, say Zone 3, you're looking at May, but if you're down in Zone 10, January or February might be your best bet for an early start. Check the GrowMore CookMore app for your specific zone timing.

Once your seedlings are big enough to handle, with a couple of true leaves, carefully prick them out into individual small pots or cell trays. They're a bit delicate, so take your time. Grow them on in a cool, bright spot. Before planting them out, make sure you harden them off properly for a week or two, gradually getting them used to the outdoors. Plant them out after all danger of frost has passed, usually around late spring, giving them about 12-15 inches (30-38 cm) between plants. They don't need any special support, just good soil and a bit of space to form that lovely root.