Fast growing small root ball evergreen - any suggestions?

Hi, I wanted to know if there is a fast growing small root ball evergreen tree I could plant in a large container. We want to block out a neighbours sitting room window which looks directly into our back garden. Tree would need to grow to about 16-18 feet and ideally be evergreen. The width of the tree should be about 6 feet at its widest. Any help appreciated.

 

I presume there is concrete or similar there, hence you need a container?

Growing a plant to 18 feet would be much easier if it was in the ground.

Don't think you are going to get anything to grow that big without a decent amount of root space (could still be in a container though)

A climber up a frame might be easiest - if that would be suitable? Clematis armandii for example (Evergreen, pretty vigorous, white flowers round about now)

 

leylandii in a huge pot could be a contender, but will take a while to get the height and width that you require

or .... a fast growing bamboo in a huge rectangular pot

 

16 to 18ft is quite some height. How will your neighbours feel about it? Would it cast their living room into perpetual shade or are they far enough away so it wouldn't really affect them, in which case it begs the question, why worry about it?