I can't imagine any of these plants would continue to produce throughout the winter for you in such conditions. They wouldn't here and I'm only slightly colder since I'm technically zone 6a. You might be able to extend the season some with a cold frame or a cloche, but there are limits to that. And yes, if you want to harvest from the plants, photosynthesis is needed since it is the green leaves you are intending to harvest.

What is the zone hardiness for marjoram? I think that one may be too tender for your zone. I know it is for mine.

FataMorgana

Thanks. I've seen several articles on the web suggesting that you can continue to harvest from oregano and thyme even during the winter if you put a thick mulch on top. Here's one:

http://www.countrysidemag.com/issues/85/85-6/Gail_Reynolds.html

The author Gail Reynolds writes:

"Covering your herbs with a heavy layer of straw can buy you months of continued harvest"

And later: "Simply lift up the straw cover, gather yourself a handful of the herb of your choice, and reposition the covering. Done deal."

But she does say that she is using this technique in the fairly moderate climate of southwest Missouri, which certainly has warmer winters than Boston.

Well, I guess I'll experiment and see what happens. I'd be curious to know if anyone else has done this in Zone 6 or thereabouts.

In a region with wet winters, mulch on Mediterranean herbs would be death. You're even recommended to keep fallen leaves from them. They need air circulation. However, if you have cold, dryish winters it might be OK.

I agree with Flora - I think such mulching would mean sure death in my winters for these plants. Or at the very least, all the above ground portions of the plants would be lost to the mold and rot such a covering would do. I can't imagine much different results in other Northeastern US locations.

FataMorgana

I grow common thyme and lemon thyme in the ground in zone5b without mulching it. But oregano and marjoram, I have to grow them in the pot and move them in the garage for the winter. They will not survive winter outside here.

Thanks for all the advice and I'm really glad I asked this question. As I read various articles on the internet about winter mulching, it looks like maybe the idea is to mulch *around* the plant so as to maintain uniform soil temperatures around the root and therefore prevent the ground from heaving from freezing and thawing, rather than to keep the plant warm which is what I originally thought.

In that case I wouldn't put the mulch on top of the plant (though that one article I mentioned does seem to suggest doing that -- though maybe I'm misreading it).

And maybe the thyme will be fine unmulched but not the oregano. I'm hoping the oregano will at least survive my 6b winter if not keep its leaves green. Whether either the thyme or oregano will remain green during the winter is anyone's guess, but from what folks are saying I shouldn't be surprised if they don't.

Thyme and oregano should survive the winter but I wouldn't expect much growth from mid November to mid February.

If the plants are big enough now you could try drying some for winter use.

Thanks, GJCore. Even though I shouldn't expect much growth from mid-November to mid-February, do you think it's possible the oregano and thyme leaves might stay green and harvestable during those months?

Oregano survives here in the snow, cold, and ice of Western NY State. I mulch nothing. Sage, thyme, english lavender, oregano, roses, etc. all survive with no problems. Drainage is key to winter survival. Pooling water = death. Of note, I was originally zone 5 and rezoned in the last zone map updates to 6a so oregano (Origanum vulgare) should survive your 6b with no problems.

FataMorgana

Thanks, fatamorgona. That's great news that the plants survive through the winter. I'm curious if the leaves of thyme and oregano stay green and harvestable during the winter?

Oregano dies back to the ground. Thyme retains its leaves but the plant goes dormant and often looks more purple than green through the winter. So no and no.

FataMorgana

Even here where they all stay green I find the flavour less strong in winter.