Many of our local nurseries inventory trees in 15 and 20 gallon pots. If not you could buy one in a smaller container and transplant. Twenty feet tall might be a stretch but many are twelve to fifteen tall. Be aware of the growth habit and rooting habit of your selection as the tree will eventually become root bound. I have some 1.5" caliper Corkscrew Willows in 20 gallon containers and they are doing well.

Is a tree in a container your only option? No nifty retractable awning systems or wooden lattice 'walls'? I've seen really cool looking treatments where a large piece of brightly colored canvas is lashed to two opposing posts with grommets and roping. Very nice looking, simple to install, taking far less room than a large container, and much more effective to boot.

Just a thought.....

If you do go with the lattice, you could plant some really lovely vines...

Thanks for all the advice will now look at all my options.
great ideas.

What will grow in a pot that will reach 20 feet high?color>

Nothing that won't blow over in even moderate wind. Anything that will grow to 20 feet (More than 2 stories. That's tall for any container!) is going to create a fair amount of bio-mass & therefore wind resistance along the way. Any tree will certainly topple, unless the container is very wide and heavy, and then you risk the container remaining stable, but the tree toppling because the root system might not offer suitable anchorage because of container confinement. Even trellised plant material would need to grow on a securely anchored trellis.

Perhaps an inorganic solution like the one Dorie (Rhizo) mentioned would be more practical?

Al

I was wondering if anyone would bring up the wind issue- thanks Al.

There is a garden bed on my new property, near the foundation. There are established plants in it - A Rose of Sharon Tree, and a Fuschia. These have been planted in about 7" of pebbles, Beneath that is a large piece of hard plastic. I don't want to have to rip this all up. Can I just add compost and hope to gradually enhance this mess? Thanks, Madeline Bruce, Nanaimo,B.C. Canada

An update on the tree in a pot. I bought a 65cm planter and a metal pot mover, which I have fixed to the base. Now I will look at which tree to plant. Never thought of the wind problem, but I have a rail round the deck so I could attach it to that some how, any ideas? Thanks.