Often when shrubs grow the energy goes to the buds at the growing tip. When you look at your picture you can see how there's a lot happening at the tips - and the stems are just holding it all up.

In amongst all that there will be new sprouts. You can usually tell which they are because the wood is a different colour - often more brown-y than the old wood. That's your 'last year's wood' in the making. That's the wood that will be using summer to create buds for flowers.

I suspect the main reason it says to leave the pruning to spring is so you can also deal with any frost/snow damage.

If you take a look at the old stems you might find little (seriously little) buds along the bare length. They're dormant. However, if the growing tip was damaged - or removed by a pruner - then those buds would get the chemical message to start into growth.

The new wood that they produce will usually be shorter and slimmer than any suckers or sprouts starting from the base. However, they will also produce flowers when the wood is old enough.

If you've decided to have a stockier shrub than the one in the picture then you would cut back the old stems (at least some of them) 'hard' to a height that suits you so they'll resprout from lower down.

You'd leave your new wood to mature and set buds. You'd sacrifice some of your new wood up there on the tips to bring the height of the bush down.

Take a couple of years to do this - part this; part next, so you still get the flowers you enjoy (though perhaps not as many as you'd like.)

It might also be useful to apply a serving of good compost and/or a helping of a general purpose fertiliser to promote the growth of new wood. If you have reliable water over summer do that earlier rather than later. It's vital that the new wood has plenty of time to harden and get set for winter, otherwise the frost will wreak havoc with those juicy sprouts.

Thank you. It's dark out now, but I will print this out and take it to the bush tomorrow and see if I can make the distinctions between all the wood bits. I'm sure I won't have a problem. You were very clear. Thanks for telling me to do this over a few years: I tend to go a bit nuts with the pruning shears!

If it is one of the smaller varieties, just cut it to your knee every spring, then take out a few of the thickest canes.