I have a large Deadedra at the side of my pond in the back garden. It`s 20 foot high and a 15 foot spread and getting a little out of hand. Can it be topped and the spread cut back if so when and how severe can I be

I don't know what a Deadedra is, and neither do my encyclopaedias nor Google...

Could you mean Deodara, which is a type of pine?

Good thinking batman! I've been racking my brains for something similar, Sid, came up with zilch...
Flowerman, if it is Cedrus deodara, this tree cannot be pruned - once it gets too big, you need to get it out and replace it.

Could it not be trimmed back Bamboo, so long as he doesn't cut back into old growth?

If it really is Cedrus deodara I'm not at all sure how you could prune...

No, Sid, this tree will not tolerate it

Good job you're here Bamboo LOL

Is it? I have no doubt Flowermanx will give it a shot anyway, though;-))

I hate to disagree - but I KNOW I've seen one with its top removed - on GOY - I remember it because we have a Cedrus deodara in the garden. The person to ask is Bluespruce....

I didn't actually like the 'look' of the tree like that, so we didn't top it in the end...so to speak...

I think we have to accept that some plants outgrow their welcome. Dig it out and plant something more suited to the space. A planting opportunity!!

You're right Spritz - any pruning takes away the beauty of this tree, its fabulous shape and those lovely drooping tips, not worth it.