Just started veg in greenhouse

I've never used soil blocks. They look like they'd dry out quickly. How do you water them? 

Just got round to making my soil blocks, most of my small seed for veg are in them (see pic). Hoping my success is repeated this year using the blocks. The trays are also on heat mats, but I can't find big enough covers for the tray, cling film maybe? Also got spuds chitting away, which will be planted in the next couple of weeks.

I am thinking about giving soil blocks a try currently I sow in small modules and pots. It is said that the air pruning achieved by growing in blocks helps the plants establish when planted out, did you find that to be the case?
One thing I really notice, not related to your post though, is how much bigger the seed potatoes are in the UK compared to France. Seed potatoes down here are generally about 25 to 40 mm in diameter .

Just got round to making my soil blocks, most of my small seed for veg are in them (see pic). Hoping my success is repeated this year using the blocks. The trays are also on heat mats, but I can't find big enough covers for the tray, cling film maybe? Also got spuds chitting away, which will be planted in the next couple of weeks.

Never heard of soil blocks before. Can I have more information please?
Thanks