I wintersowed mine both last spring and this spring. Mine have already germinated having been sown in mid January. I planted them out and protect them on frosty nights with a piece of plastic sheeting over the bed. I would go ahead and wintersow them now. Place the container in full sun and you should see sprouts soon.

Headed cabbages are best sown in late July for you. That should give you a nice 90 day window to harvest. If you're doing any Asian varieties, you can sow them a little later since you're more interested in harvesting leaves.

The Burpee Earliana is what I sowed as well.