Here's a tip if you're sowing tomatoes at the moment. Sometimes when the seedlings first emerge and straighten out they still have the seed husk stuck on their head. It may come off as the seedling grows and expands, but more often than not it stays there and the seedling is effectively strangled, unable to free itself. When this happens, try putting a drop of water on the head of the seedling. The seedling should then be able to free itself within a few hours. If not, moisten it again until it does.
The problem arises because the seed husk dries out and contracts once it's elevated out of the soil, and if the seedling still has its head inside it when this happens ... ouch.
Never ... (I offer the rosy red fruit of my own experience here) ... never attempt to pull the seed husk off with your fingers. You'll be sorry.
Anyway, I'm growing a preposterous number of tomato varieties this year, albeit in small quantities of each. These are the ones I already have growing as fine sturdy seedlings, and no constricted heads. More varieties still to come.
Salt Spring Sunrise
This year I'm growing them in simple coir (from reconstituted blocks) watered with a very dilute solution of organic seaweed extract. If the weather's bright and not too breezy I put them outside during the daytime to maximise their exposure to light. A day or two of winter sun every week brings them on nicely.