I'm not an expert, they may be some seeds that need cold stratification to germinate, but overall you can still WS. I doing a couple of types today that need the cold because we are suppose to get snow this weekend. We should have more freezes at night through April.

It is not too late to ws in Z:4. I have only a few containers done and have many more to do.

Most seeds do not need cold stratification and can be started throughout the early spring, summer, or fall. Perennials and cold hardy annuals can be started now. I don't start tender annuals until April/May.

If a seed needs an extended cold period you can put some damp mix in a small baggie and sow seeds in that then put in the refrigerator for the required time. When the time is up or seed has germinated either winter sow as usual or plant germinated seeds. A few other seeds need warm cold warm.

There are several germination databases that you can use.

Here is a link that might be useful: Seed Germination Database