Buying troughs. How deep or wide do I need to plant shrubs?

[Upupandiwent]

I have a long, bare fence, poor soil and I can't dig down because of pipes etc. I want to buy large wooden troughs to plant shrubs to cover the bare fence. Any ideas on depth or width of the planters I should buy? I need 6ft long. They all seem to be 39cm deep by 30cm wide. Or...40cm wide and 24cm deep. Please help, I'm a novice!

Have a look on line, but troughs large enough for shrubs are very expensive. Very large, plastic pots 50L upwards might be better and cheaper. I have bamboo in 3 similar pots that screen about 6ft of fence.
Climbers will also do well in large pots and can be under planted with smaller plants.

Thank you. The bamboo are a great idea. I'll definitely get some.
Could I plant lavatera or buddleia in a large trough or planter?

Both can be planted in pots.

Lavatera

s3.amazonaws.com/YouGarden/Web/500x500/510339.jpg
Buddleia
www.thompson-morgan.com/static-images/tandm/how-to-grow/buddleja-group-pic.jpg

What about climbers such as star jasmine, honeysuckle, etc. They can be grown in large pots (cheaper than troughs as a PP said) and grow relatively quickly. I have both growing up a fence in pots with a trellis behind them. If you place numerous pots beside each other in front of the trellis they tend to merge together and end up looking like one solid wall of plants (which is what I was aiming for!). They are also fairly low maintenance. Star jasmine is also evergreen.
Jasmine
i.pinimg.com/originals/17/7d/5b/177d5b67f1623db2fa422526440dddc2.jpg

30l tub is the minimum for a shrub like rose or hibiscus.

Deep is better than wide and shallow, as there is less surface area for water to evaporate from.

I recommend the “elho loft” series, they are chic and they also do 50l~ ones big enough for shrubs. They have a built-in reservoir reducing chances of over-watering or drying out. Get the deepest ones to reduce drying out and to allow good root growth and top the surface with a thick layer of bark or stones to reduce surface water loss.
I huffed at the plastic pots at first but i now favour them over my fancy swagged teracotta ones.

Thank you everyone! Thanks for the links @MsMamaNature. The jasmine looks lovely.