I usually sow in march/april (by the moon - but that's me!) Then anytime after the longest day (21st june in UK) when they're big enough, I make deep holes with a dibber (or a stick!) then throw a leek seedling in, and add plenty of water, then the nice friable small grains of soil follow down into the hole. The water settles the soil in. I'll give it a few days to settle in - then get a mulch on quick - to stop the weeds and keep the moisture in. They don't get any more water or feed - BUT - I do put compost on all the beds in spring or autumn. Sometimes well-rotted manure, sometimes my own made compost, sometimes the black stuff you get from the council. I also use comfrey - minced up in the shredder, to mulch as much as possible. I believe if you feed the soil regularly - it will feed you back!
Last winter's leeks were 3" across - monsters!!

You don't have to put a collar round them unless you are going in for showing and are very experienced! I ridge ours up as they get to some sort of size then keep ridging up until they are ready for use.

Thanks for your comments they are very helpful