It's as tough as old boots. I cut mine at almost anytime of the year. Ideally now, to give it time to make growth for next year

I've just given mine its annual trim. Now the flowers have finished it is just the time to cut it back but leave some greenery although it will produce a huge number of new shoots from the old wood. As correctly said above: don't leave it much later as it will need to regenerate for the flowers next May.

As an aside I have just completed a page about this species:
http://www.buddlejagarden.co.uk/globosa.html

I am interested in whether people have identified their plants as male or female.

Thank you very much. I will get trimming! I'm so pleased to find I can tackle it now as it is quarrelling for space with my sambucus nigra. Any advice on that one, Worthy? And , Buddlejagar, how would I identify the sex of the BG? Thanks both for your help.

Difficult to sex. If there are others (male) around the female will set seed but if there are no compatible pollinators it won't. This year I have a male (var. araucana) alongside my female globosa and it (should that be she?) has many more seed pods than ever before.
Botanists have to dissect the flowers and stain them to identify microscopically either viable pollen or ovules.

My RHS book says to cut back Elderberries in the winter.

I did my sambucus nigra this morning.

Thanks Buddle! Whoops Steragram! However the sambucus grows like billy oh so will be fine I expect. Mine has a few berries, however, so I will leave it for the birds. I don't understand why the shrub isn't laden with berries because it certainly had a wonderful display of flowers.

That advice will be for the big white flowered elderberries I guess. Pruning the nigra depends on whether you want flowers or not. If you don't then you can prune in winter but it you do you can prune as soon as the flowers are over. I don't think its worth keeping them for the berries as they are nothing like as big or prolific as the wild ones, not even for the birds. If you prune in winter you may be cutting off the flowering branches.

I think that advice must be for the wild type elderberry. The nigra should be pruned in March/April if you don't want flowers and immediately after flowering if you do.
(Be as drastic as you like) You can confirm this if you put Sambucus Nigra Pruning into the search box at the top right of the page (I just looked to make sure it was there)
The berries on the Nigra are never up to much and I don't think they are worth keeping even for the birds.