Woody plants in particular often require both a warm and a dry period before they come up. Some kinds may sometimes take years to germinate.

It's all about making sure the seedlings don't appear at a dumb time, like right before winter.

Right, I am waiting till the end of April, then moving the pots where I do not have to squeeze past them on a daily basis.....like alongside the coldframes at my allotment - 42 x 5litre pots, apparently containing nothing but soil are just...taunting me. I usually hang on to seedling pots for a couple of years and if all else fails, I throw the contents round the back of the greenhouse....often enough to spark recalcitrant seeds into life.

I'd wait a while yet. Today I saw another white elm coming up from seed I planted last year in the porch. Allthough the seeds had been frozen before I got them, some are coming up now after an additional winter in the unheated porch. Some came up right away last year, but there seem to be going to be quite a few more.

Staggered germination like this is not unusual with woody plants. If they don't all come up at the same time there is a better chance some will make it, whereas if there is a killing event and they are all out of the ground at that time the whole crop is lost.

Campanula, Slightly off-topic. We here in the northern U.S. and Mid-atlantic got a winter like you guys got (I think) last year. And last year wasn't a really bad winter here. Unless planting timing is different for your climate, you likely have til April before planting time is in full swing. If you have perennials and annuals already germinating, you are ahead of me here. If you have a commercial business, then don't mind me. If it's for personal satisfaction (your yard) what's the rush, right?