I'm here in eastern Massachusetts in Zone 6b. I have a few thyme, oregano and marjoram plants outside that I'd like to keep harvesting from occasionally during the winter. I've heard that I have the best chance of making that happen if I cover the plants with a thick layer of mulch, so I now have some salt marsh hay for that purpose.
But I'm wondering exactly how they should be covered. if I cover the plants completely with several inches of hay, I'm sure it would be warmer for them, but I'm worried that it would totally block out any winter sunlight that I would imagine they would need to keep the leaves green. I can't imagine that photosynthesis completely stops during the winter. Or does it? It seems that being exposed to as much winter sun as possible is one of the ways that the plant would manage to keep its leaves green during the winter, no?
Protect from wind and frost burn, they are going to be growing so slowly you won't see them have time to turn white, cover and uncover if you have any worries, but these plants may freeze to roots even with covering- but return in warmer weather. Good luck