Its okay to do that in winter?

Yes.

Late fall/early winter after the ferns have turned yellow and dried is the correct time to cut the ferns off at ground level. I then do as Rodney mentioned and top with a couple inches of compost , add a little balanced fertilizer, and 3-4 inches of shredded leaf mulch.

I leave the dead foliage alone (because I'm lazy). It works well to mark the area where the plants are. I try to cut them to ground level before the new sprouts emerge in the spring because if you don't do that, it is difficult to cut the new spears.

Linda

Jeff, I am a bit south of you. I generally leave the dead stuff up until late February. My reasoning for this is winters can be a finicky thing here and my hope is that foliage will help to catch precious snow. I often scratch in fertilizer in early June when I am done harvesting and put a new layer of straw mulch down then.

If you get Asparagus Beetle you need to remove overwintering debris before the overwintering adults emerge and lay their eggs on the emerging spears. So I'd get rid of the old growth early.

I suppose I should have added that when I cut them in the end of February, I also pull up the old mulch and put the old mulch plus the old foliage in the chicken pen. There is still plenty of cold weather between then and my average last frost date of May 15 to help keep the asparagus beetles in check.

Ha - I could do with a chicken or two to deal with the beetles.

My chickens will get into my Asparagus jungle after I have let them fern out after harvest but I'm not sure how many beetles they eat. Most of the beetles and larvae I see are towards the top of the ferns, but maybe I just don't see the ones lower down in the jungle. I try to limit the time they spend in the patch because I don't want them scratching down to far and damaging the crowns.