I think you will be fine, but you will need to water more often if they get 'high-noon' sun.

Just wondering.. why would you wrap planters in plastic of the winter?

Ohhh.. if you are planting larger flowering dahlia or tall specimen be sure the planter is heavy enough so it can not get knocked over in the wind.

Keriann~

Thanks for the answer, I'll be covering the planters on the deck with plastic, to keep them from filling with water, then freezing and bursting--least thats my thought.
The other thought was to make loops on the back of the planter (outside) so I can slip rebar down for support.

Oh I see... that makes sense.

I have two large pots that I have drilled extra drainage holes and then pounded rebar (5' tall) through them about 1/2 down to 'stake' them down. I grow large trees in them and the wind was a problem. But these are on a gravel walking path... your idea sounds great for a deck!

Keriann~