How to trim my rosemary?

About 4 years ago I planted a new rosemary in quite a sunny spot. Now it seems to be falling apart - I mean, the centre is empty and all the branches are falling outward. Other than this shape it is healthy. How, and when, should I trim to center it again?

 

I should take cuttings and when they have rooted dig out the rosemary. Cheers, Tony.

 

I can't remember how I did that, do you just take a cutting and put it in water till it roots?

 

When I take cuttings of rosemary, I tend to pull off sideshoots about 2-3 inches long, so that there is a little heel from the main stem. Remove most of the leaves, so only 4-6 are left, and either stand in water until roots show (not done that at this time of year, TBH, but certainly works in the spring), or space around the edge of a small pot of compost...

 

You can cut rosemary back really hard and it will usually bounce back. I normally cut mine back in spring, but I have done it in the middle of winter when heavy snowfalls have broken branches off and it's never done it any harm.

 

I've hedged my bets: trimmed back hard, took cuttings, and am drying some for cooking. And put some in the shed to keep the mice off my food stocks! Thanks for your answers.
See also http://www.ageless.co.za/herb-rosemary.htm.

 

Lorea is right; you can cut it pretty hard back and it will regrow as long as you don't cut it back to bare branches. Having said that it can still grow lopsided and straggled but that is part of Rosemary's charm.

 

I just left a few needles ..... but used all the cut-off rosemary wisely!