Box! oh just read the size requirements... you might need several pots. Ivy, Bamboo, a Yew....
If in a pot they would need to be watered regularly and fed.
What are you trying to hide behind this plant?

12ft x12ft I dont think thats possible to achieve in pots?

i am trying to hide an unsightly garage behind my garden fence.the fence is 4x4 .and the garage sits higher !i am willing to use perhaps 2/3 large pots

Have you got it right as 4m is an extremely high fence that more than 12foot high? or if so I wonder have you considered planting in the ground instead self clinging climbers such as Virginia creeper or Ivy they may give you the cover you want?

Agree with Drc726 :)

Agreed! 4 metres high trees in tubs won't work - not enough root space, not stable. Even if you could get the trees / shrubs / bamboo to survive they'd be constantly blowing over. This idea's not a runner, sorry!

You would need pots at least a meter in diameter, and a meter deep, ideally concrete, to support the shrubs properly.

SORRY... just checked measurements 2.5m(H) x4m(L),has to be in pots as the floor is an old garage base and no chance on getting in to ground

That's still over 8 feet high. You might get something lighter like bamboo to grow in big pots. To cover 4 metres wide (more than 13 feet) you'd need that width in pots. So 4x 1 metre wide pots would do it. Why not paint the garage wall. If it's not on your property you could ask the owner. Do you feel a mural coming on?

Thanks for remeasuring but I still dont think this will work? Have you thought about how much water this would need? I still think climbers are your best bet so how far away is some soil? Because a Virgina creeper is vigerous and reaches 60-70 feet also Hops would cover this area.

I like the idea of a mural....maybe a mirror to reflect garden stuff and make it look like a door in the wall!
I'm getting carried away now :)
Have you got a photo of the area?