We have limited access to fresh herbs here in the cold North winters, but the needles from Pine family (including hemlock, fir, and spruce - but not the toxic Yew!!) are high in vitamin C and available year round, especially here close to the boreal forest. Also wintergreen, as indicated by it's name, is fresh even under the snow, and has aspirin-like qualities similar to willow.
This time of year, before frost, we can harvest asters and goldenrod, and many plants to dry before they die off or back. I'm also planning to collect seeds from the wild yarrow and St. John's wort on my property to try to grow them from seed next year. I'm hoping to start a medicinal herb business, starting with selling potted herbs that I grow from seed. So I'll collect seed soon, and then I think I'll probably stratify it starting around New Year's, and plant under
lights in February. I also think I found some New England Aster growing along the side of the road in a nearby town, and I'm going to try to get some seed from that as well and introduce it to my property, which only has white aster (New England, which has deep purple petals, is apparently the most effective aster for lung ailments, with the most resinous flowers).
For me, winter is the time to play with all the herbs I collected and dried during the growing season, making tinctures and salves, and of
course, using the herbs to keep colds and flus at bay, particularly the immune-enhancing ones like astragulus and echinacea (and garlic - I love garlic!).