Apologies but I can only comment on the Fatsia (sometimes known as the Castor Oil plant) - if you look up a picture you'll know if it is. I'm assuming your height is 800mm which on my iffy calculation is about 3' 6''.

Fatsia need not be pruned but if getting out of hand then trim in Spring.

If it is the true Castor Oil (Ricinus) I believe it is a tropical tree and I have no experience of them.

Just to add, if it is the true Castor OIl plant (Ricinus) it will die outside in winter being as noted above a tropical plant.

The False Castor Oil plant (Fatsia) as John says can be pruned in spring either lightly or back to heavy wood from which it will sprout quite happily. Just under 3ft if 800mm (80cm) so I wouldn't think it would need pruning yet.

There was a discussion on here about Fatsia last week they suggested that the leaves are bent over now to protect the crown. Here in the south east I havent ever done that, but north of Watford it is often much colder! I have never pruned either of mine and they are both at least 6ftx4ft with lots of flower heads through the summer.

No they do not need pruning. They only need a trim if they are getting too big. Mine is 6 feet x 6 feet and I give parts a little tidy up from time to time but regular annual pruning for a plant your size is not required.

All the people that live just south of Watford must be breathing a sigh of relief that they live in the tropics then Lol.

Oh Fractal - we southerners think its cold here but compared with with the rest of the country we often get away with it in the garden as rarely are our cold spells prolonged.