I multi sow my leeks. That is, I sow them in clumps as starters and let them grow in a group. My leeks are nearly all harvested. But they are still producing even now in January. Despite the cold, and despite the snow. One benefit of doing a no-dig compost mulch is the soil does not freeze as much or as hard as my sub-soil clay would. Making harvesting much easier, even at sub freezing temperatures. But what is important is the end result: a lovely fresh garden leek ready for slicing into my winter soup.