When to prune rhododendron

[schloss]

Hi,
As the title says really - have very tall 15ft-20ft high rhododendron which are flowering, but now blocking some light so need reducing in height.

The issue is conflicting advice on when and how much to prune. As they have just flowered, some advice is to prune now, other advice is after Christmas.

The question is which is the best time and how far can I reduce the height in one go plus do I just take the height off and/or shape the whole plant? Just for info we are in an area where hard frosts occur if that is important.

Thanks in advance if anyone can provide help.

I'm interested to find out the answer to this, too. I wanted to prune one in the autumn, but every time I looked it up, most advice said they didn't really need pruning!

Ours has flowered pitifully this year. I didn't deadhead it until spring though, so I think that's why.

I have pruned my very large ones now, as new growth will grow from the bottom, but it needs light. I have taken out the very oldest branches to let light in, but have left some as insurance for flowers next year!
I started this cycle of pruning last year, as all the growth was at the top of the plants 8ft up. This year there is strong new growth lower down and some has flowered.
They seem to be quite tough!

Yes all the info online which says do not prune, obviously aimed at pretty dwarf plants not gigantic ones!

Thank you JT05 that has given me the push to start pruning now! Just one question, did you only prune the smaller branches or thicker branches which I will need to use a pruning saw on?

Thanks.

I have an azalea in the front garden. Sort of the same family of plant/tree/shrub . I attack mine with the hedge trimmer after it's flowered . Cut away all the scraggly bits at the bottom . It must be quite hardcore as it flowers beautiful every year

I cut away the thicker bits down to the main trunk, if they were old and blocking the light.
A good rule of thumb when pruning any bush type plant is to remove one in three of the old stems.