If the deck is walled on three sides and covered with a roof, can we presume it is not shade you're after, but screening? It would help if instead of just describing your idea of a solution, you'd describe the problem. What benefit are you trying to accomplish?

BTW, soil is very heavy and potted trees can weigh tremendous amounts. Consider if this might be damaging for your home. (Most 2nd floor decks would not be designed to accommodate this type of weight.)

Thank you so much - I hadn't considered the weight issue, and I'll have to confirm that it's OK.

My deck is small and looks out over other townhouses; and I thought some evergreens could make it look more like a garden. If you have other suggestions, I'm eager to hear them!

I agree with the comment about shopping in person - I purchased one tree online and returned it as soon as I saw it. But what kinds of stores have these on display? I haven't been able to find any.

Most tree form plants that would survive winter in your zone, in a container, are going to need plenty of sunlight. Too, getting plants to survive winter in a container is sometimes tricky. I think you'd be better to focus on "patio" plants that enhance the area during the warm season, and then just clear those things out during the winter ... when no one expects there to be a garden on a balcony. Some tropicals could move inside, if you have the space and conditions. Or, you may need to treat things like annuals, getting rid of them at the end of the season and starting anew every year. I have a balcony, too, and grow a variety of things just to have some life and color. In the winter, things mostly just exist but don't look great. (I'm in Florida so have a significant advantage over your location.) Things I've grown include tomatoes (they get messy looking), Thai crown of thorns (one of the better plants for flowering), Caladiums (an easy, colorful annual that can be saved for next year), orchids and bromeliads (the easier ones ... great for color and form). Plants that do not spread out sideways too much work out better because of space constraints. This summer, I added water chestnut to the entourage and think highly of it for a patio plant. I like that it gets tall, the foliage is vertically oriented and, being an aquatic plant, cannot be over watered. One just tops off the container every couple of days. It's about 3' tall now but supposedly can get to 5'.

(Next year, I'll get a better looking container!) :-)

Wherever you want an actual tree form, you'd probably be better off in the long run with an artificial plant. It wouldn't have the weight problem of a real "tree" and it wouldn't have any light or water requirements. You'd just need to get something that fits and looks good.

I did buy a dwarf Alberta spruce for the deck, but put it on the front porch when I recognized the deck's sunlight issue. It will be my experiment to see if a container plant survives the winter here.

I really wanted plants on the deck for the winter season, though - I imagined looking out from my dining room table to see greenery instead of houses, maybe with some festive lights on them for the long winter evenings.

I'm afraid artificial plants are the best way to go - I'm just having trouble finding any that I can see in person before buying. Shopping online is tricky because if I don't like what I've ordered, the return shipping will cost a fortune.

Check out Home Goods or Home Depot. HD may not have them in stock but they can be ordered and easily returned to your local store if you don't like them. Another good selection is carried by Nearly Natural and they have free shipping and free returns. I'd also check out Wayfair or Grandin Road

Thank you so much for the tips - I hadn't heard of Nearly Natural, and they have some things that might work. I'll let you know how it turns out ...

Just ordered a potted cedar from Nearly Natural!