Posted: 17/03/2013 at 15:11
If they are container grown plants then most times of the year when the soil is 'workable' ie not when its frozen. Spring and Autumn are the best times to plant trees/shrubs.
Sounds like you've got a bit more scope with the trellis aswell. If the pot you use is big enough you might get away with a climber aswell? Although i wouldn't encourage you to overcrowd it.