I would like to grow green leafy vegetables such as lettuce, kale, collard, bok choy. Can someone share their experience as to which ones you can grow in north easy I'm in Zone 6 upstate NY.
I gardened in zone 6b, central Ohio. I couldn't start planting until some time in March. I usually celebrated what I called "the planting of the green", meaning peas and other cool weather crops, about St. Patrick's Day, March 17th. The soil simply was too cold until then. If the soil is too cold, the seeds will likely rot, unless of course, the birds get them first. A soil thermometer comes in handy. There is usually information on the seed package giving a range of germination temperatures.
Now, inside some kind of cold frame structure, I did keep some mixed lettuces until almost Christmas a few mild years. But these were already established plants, not seedlings. They didn't really grow a whole lot, just kind of a stasis thing, but darn it did feel good. I'd just take all the seeds I had left, mix them together, and just broadcast seed them into the designated area. If I remember correctly, the red varieties performed better than the green ones.
I never had any luck with spinach, spring or fall, although fall was better. Sometimes I had luck with trying to overwinter some spinach though, assuming a mild winter, one with enough snow cover to protect the plants. I know that sounds odd, snow cover to protect, but it prevents the cycle of freeze and thaw to a certain degree, as well as frost heaving of the plant. Spring warmed too quickly, and it would just bolt and go to seed, in a very short time. Annoying.
I'm not a fan of cruciferous greens, so I can't speak to them. I do believe most of them prefer cooler weather though.
And, FWIW, green onions (aka spring onions or scallions) will overwinter, but may go to seed early in the spring following the winter.
Johnny's Select Seeds has a really fun selection of all kinds of greens.
Of course, this time of the year there's always the set of sprouting jars in the kitchen.