Winter Mulch for perennials
May I please have guidance on winter mulch.
I am in Ontario on the north shore of lake ontario near Toronto.
I have read that I should use winter mulch for some perennials like german iris. But I am very confused about when to put it on. I've collected a whole bunch of evergreen boughs and I put them on some more tender perennials a couple of days ago because the ground seemed pretty frozen. but maybe it was too early? Now it's raining. Did I put it on too early? Should I take it off and wait till later? I seem to remember reading that the ground was supposed to be frozen to a certain depth but not sure how I would verify the depth of freezing?