This is over my head, but best as I know, evergreens are for the most part dormant during winter, meaning they are not actively putting on new growth. Thus, they do not need light for photosynthesis because they have shut down operations for the winter. Just think of winter as a "pause" button for evergreens. Again, speculation without much factual knowledge behind it, but others can hopefully chime in with their expertise.

I am not a tree/shrub person by training, but as an example, I keep my strawberry plant covered all winter and the leaves stay green all winter, then it comes back to life in Spring. So my hunch is that evergreens would not be damaged by covering in winter, as long as you don't trap moisture (use porous material).

Snow is an excellent insulator because it traps air, so deep snow that lasts through the worst of winter is a great protector for plants of all kinds. Styrofoam and other forms of plastic do not allow for air exchange, encourage molds and fungus, and do far more harm them good despite the claims made for various devices. Don't use them.

Evergreen boughs, burlap screens, air permeable landscape fabric, anti-dessicant sprays can protect evergreen and other plant types from the dessicating effects of winter cold, sun and wind .

where are you???

NEVER.. i mean NEVER.. cover any live plant with plastic ... whats that all about ...

its very simple ... in my MI ... its not the cold... its the repeated thawing and freezing of tissue.. due to winter sun and winter winds.. that desiccate leaves until they are freeze dried.. and dead.. and if it does that under the bark.. then the plant is dead ...

being buried in snow.. removes all wind ... and direct sun ... fat and happy ... [presuming it isnt crushing them]

my usual comment is.. get them dormant.. keep them dormant ... and that is your goal with winter protection ....

and i have kept many a plant.. in my polebarn most of winter .. dormant plants do NOT need sunlight ... [but the pole barn is 2 zones warmer.. and creates its own problems in late winter ] ...

so thats the overview in a nutshell .....

ken

BTW: most winter protection.. is a burlap wrapped around a plant .. leaving the top open ... NOT COVERED in toto ... and that allows the LIGHT [as compared to sun] in ... and allows any trapped heat out.. and completely removes that darn winter wind ...

But it sounds as though it is genuinely true, that green plants can be kept in COMPLETE darkness for the winter months, and not suffer for it?

My present evergreens are mainly Mt. Laurels and Hollies but this past winter, the deer nearly destroyed them, and so next winter I want to cover them mainly to protect from deer. These plants have generally not been bothered by deer in warmer months.

I'm in Z6, but I wanted to try growing some Z7 evergreen plants, and was intending to protect them in the winter, so that has also prompted my question.

Winter protection from sun and wind can make a real difference in an evergreen plant's chances for survival, but such protection has a very minimal effect on actual temperature. In other words, if a plant is genetically hardy to 0 and you experience frequent and/or prolonged lows of minus10, it's unlikely to survive no matter what sort of protection you use. (Snow is a different case entirely. Plants buried under deep snow may not experience temperatures much below freezing even if the air temperature is well below 0.)

So,is it worth trying some Z7 plants? Sure. Look for areas of microclimate. Use burlap or landscape fabric - on a framework of some sort, not touching the plant. Such protection can trap just enough ground heat to make a few degrees difference. Sometimes that's all that's needed.

to repeat ...

a dormant plant.. if truly dormant ... [setting aside your zone pushing idea] ... does NOT need a lot of sun ...

what for ???? .... it can NOT process it for anything.. its dormant..

ken

ps: a stressed deer.. will eat anything ...

I think it matters what kind of plant you are talking about and where you live.

The local chapter of the Camellias society, for example, recommends covering newly-planted camellias with Microfoam. This has some micropores which allow for some air circulation, but does also allow light in. These plants are often in bloom when the Microfoam is removed in Spring, so yes, they do need light to develop those buds and bloom!

Some evergreens will continue to grow just a bit in our zone in winter. Hellebores for example, some evergreen witchhazels, and anything else that blooms or develops buds over winter.

dave11, I think the answer to the darkness question for most plants is yes. I think you can safely cover most evergreen plants in winter (again, with breathable material). I can't think of any evergreen shrub that actively grows in winter with the exception of those that bloom in winter or very early Spring as mentioned.

Shrubs aren't usually evergreen because they want to grow during the winter. Usually it is because they gain an advantage in not having to expend energy making new leaves in Spring, so they make anti-freeze for their leaves instead.

Plants only grow when they are happy. Winter is not a happy time, so most become dormant and wait it out. Thus, they really don't need light because they aren't growing. Most are programmed to know when to emerge from dormancy based on the length of day, temperature, etc. If you were to continue to withhold light at that point the plant would start to suffer -- they can't maintain dormancy forever.