[Growster...]

Weve got a rather tall expansive lilac, which some years has a huge array of blooms and other years, they're a bit indifferent. I reckon it's about 24 years old.

The tree (it's too big for a shrub now), needs cutting back to a reasonable size, as it is over 12' at the moment, and getting in the way.

Does the team have any tips for timing, and how much we can take off please?

[Sparkyrog]

I have a lilac hedge which I got annoyed with ,I cut it back and laid it ! it never flowered if I am late trimming now it does . Probably needs feeding though   

[mumofstig]

I always cut mine back after flowering cos, otherwise, it tends to overhang the greenhouse.

Cutting it now must give it enough time to grow flower buds cos it flowers regularly  but I suppose this depends on just how hard you're planning on pruning it. 

[Yorkie]

I've looked it up in my RHS book on pruning:

Prune in midsummer after flowering, or renovate (major work) in winter - so timing depends on what you're trying to achieve.

Midsummer pruning = deadheading with secateurs to avoid damaging the young shoots which will flower the following year.

Renovation = Cut back main stems to 1-2' from ground level.  Regrowth should be thinned but flowering is likely to be delayed by up to 3 years.  It is preferable to stagger hard pruning over 2-3 years.

If renovating, remove side branches first to make life easier.  Cut straight across when cutting down to 1-2'.  To prevent tearing by heavy branches, consider doing the first cut about 1' above where the final desired cut will be - then cut the final 1' away.

No need to treat cut surfaces.

Feed well and mulch.

In the next dormant season, thin the numerous shoots (from the pruned stumps) to 2 or 3 strong, well-placed shoots per stump.  Remove any further surplus growth and suckers.

[Trillium]

I did the same with mine, pruned them after they finished flowering. I just hacked mine back to a good shape that doesn't get in my way with the lawn tractor, and past the point where the flowers just finished. I have another lilac that thinks it's a pole bean so it will get it's head hacked off very soon so it can put out side shoots this year.

[Growster...]

This is very helpful Folks, thank you for such good advice.

Staring at it now (which is somewhat difficult at 6.45am with only one mug of tea), the real greenery starts at about 6', and then forms a canopy which extends over 12' easily.

I reckon we need to cut it right down so the 'trunks' are about 4' off the ground, so from there, the new branches can get going again.

Does this sound about right? I'm not too worried about missing the blooms over the next few years, more to the point, I'd like to keep my car aerial as well, as that always gets clobbered every time we reverse out of the drive!

[Yorkie]

I guess you could do a preliminary prune to 4' now, and then go in hard if you want to over winter.

[Growster...]

I guess you could do a preliminary prune to 4' now, and then go in hard if you want to over winter.

Sounds about right Yorkie, thank you.

I have no problem getting rid of the branches, and of course, half a dozen cuts at 4' is much easier..;0)

Reading your first post again, I can understand the regrowing part, as somehow Mrs G has managed to get several of these going over the last couple of years, mainly because she got so fed up with asking me to do it..;0)