I will just copy and paste what I said on here in January 2018, nothing has changed.
I sow my Leeks around April in an unheated greenhouse in 4 inch deep trays. They germinate in a few weeks.
My choice for many years has been Musselburgh.
At end May or first week of June I plant them out when they are about 6-8 inch tall.
Plant in rows, six inch between each row.
Use a dibber (well old cut down brush handle) to make a hole about 4 inches, as with the root the leek sits proud a good 2-4 inches above the soil. Make a hole every six inches.
Fill hole with water and drop the leek in (I do not trim my roots), then over the day keep topping the hole up with water, trying not to break the top edge so it does not become a muddy bath.
Grow them all around the plot but the majority in a raised bed. You can grow things between the leeks when they are growing like radish.
Nothing special compost wise, just a light dig over in the spring and work in lightly some of my homemade compost.
They prefer the soil to be firm or they flop over, so hence the light dig above.
My variety produces from late October through to March. They are tall plants and produce a good upright leek all of the same size.
Never get any problems at all with my leeks and nothing seems to want to bother it insect wise.
Here are some pics;
