I have a 4-year old erica lusitanica with a main stem which is now reaching
4ft tall. I would like to reduce the height by about 50%. but my book says
I shouldn't cut into the old wood... There is plenty of new growth at the
bottom and I thought that cutting back the main stem might improve the shape
(make it more bushy). Can I do this and, if so, when is the best time -
it's just finished flowering...

Willobie