I chop mine back by quite a bit each year, but it makes about 5 ft growth a season now. I have new ones spring up one month and the next month they're about 4ft tall, so i'm probably not the best person to advise about stopping growth ;D. They tend to be vigorous (not just in my garden) so you need to keep an eye on them. nipping the top out will certainly help, and also help them bush up
I have two, that were grown from seed about 3 to 3.5 years ago, and between them they cover fencing about 8ft high and 30-35ft long :o. The trucks on them are about 3-4 inches at the base. Vigorous pruning may have stopped them in their tracks earlier, but I specifically wanted them to cover the fence. My neighbour a few doors down has one and has had similar experience.
It may be they just like the soil, and hard pruning will help.
Dawn
PS if anyone wants a seedling(s) I can try to dig one up and post [not sure how successful it would be but willing to have a go] - they only get pulled up here.
