I never trim my gilliesii, but here's what a phoenix reference recommends for pulcherrima:

In the early spring, after the danger of frost has passed, you should cut this shrub back to 6 to 12 inches above the ground. As soon as the weather heats up, it will explode into growth, growing to 5 to 6 feet tall and wide in one summer. Deep, weekly irrigation during the bloom season will keep plants healthy and prolong the flower display. It performs best in full sun and well-drained soil.

So... Looks like it's best to leave it leggy through the winter and then prune after frost danger is passed...

--Bob

Here is a link that might be useful: Got that info here

Is P.gilliesii hardier than P. pulcherrinum? I have some plants that I raised from seed last summer, they did not grow very big, but were healthy. They've been in the greenhouse all winter and now seem to be dead, the stems being greyish-looking! Is there any hope that they'll send up shoots from root level? They've had frost-protection, most of the time. I don't think I've ever seen this plant growing or offered in the UK, maybe it is just not really suitable?

C. gilliesii IS quite a bit hardier than C. pulcherrima. The former will take temps to at least 10F/-12C with little damage, whereas the latter will be toast at about 27F/-3C. There is a form of C. pulcherrima that is slightly hardier (with no thorns), but only by a little (to maybe 25F/-4C). C. gilliesii likes heat and prefers to be on the dry side, although it will grow well for a few years in high rainfall areas.

Can either of these plants be stored away for the winter in a cool garage with little light and little water?

I'm using this method to overwinter stuff like dwarf pomegranates, bananas, bouganvillea, plumeria and tropical hibiscus.

I'm not sure that I have the space to winter any more plants that require enough light and heat to stay in active growth....

Thanks,

Dan