Fuchsias Definitely On The Up. Why Now?

The fuchsias are definitely on the up, as this strong new growth illustrates. Although those kept over 4 deg C have never shut down - despite a couple of false alarms - and have been growing very slowly, growth seems to be much faster and stronger since the winter Solstice. I don't know why this should be. They seem to know better conditions are on the way, that we are gradually coming through winter.

It can't just be day length or temperature, since until recently temperatures have been fairly constant (within a range), and the days were the same length or longer at the end of last year. Why were they not growing as strongly then?

CAN FUCHSIAS DETECT CHANGE IN DAY LENGTH?
Most living things have an internal biological clock called a 'Circadian Rhythm' which they use to measure time. Is this the case with fuchsias? Or perhaps they are measuring the CHANGE in day length and thus know that day length is increasing. There doesn't seem to be any evidence that plants can do this (they just measure day length, the 'photoperiod' (actually, they measure the length of uninterrupted darkness)), unlike animals such as domestic fowl and other birds, for example, which lay eggs in spring (increasing day length) and moult in autumn.