Posted: 12/01/2014 at 17:24
As a general rule on pruning berry producing plants, prune them after their berries have finished to give them as long as possible to produce some more.
So for example Cotoneaster, the berries are being picked off by birds into the winter, so prune in early spring.
In my experience, sorbus/ rowan, cotoneaster, and lycestera formosa don't need male and female plants, but holly generally does and the varieties in catalogues will often say whether they are male or female.
For more info see: http://www.egardenplace.com/index.php/nursery/do-i-need-a-pollinator-for-my-hollies/