Ivy is traditionally the feminine partner to holly, although some schools of thought take the opposing view and consider it to be masculine, due to its white berries which are said to be symbolic of semen.
Ivy is thought to be protective in nature and if grows on the walls of a house, those inside will be kept safe from misfortune. My Mum's name was Ivy and she certainly went out of her way to keep us all safe from harm.
In times past it was considered unlucky to bring more ivy than holly into the house at Yuletide, however, this was probably due to the fact that patriarchal society wanted more masculine plants in the home rather than feminine. Balance again, I feel is the key to harmony.
Read more in 'Mrs Darley's Pagan Whispers'