Follow this advice to determine if your holly is male or female.
Q: I'm told that you need to have a male and a female holly in order to get berries. How do I determine if I have one of each? And two years ago I bought a holly that was supposed to be berry-producing but so far it hasn't produced any. What's up?
A: It's true — for most hollies, there are males and females and you need one of each in order for the female to produce berries. Unfortunately, you can't tell by looking at the plants whether they are male or female. You can make the determination by dissecting the flowers, but even this is difficult because the flowers are so small.
Nursery-grown hollies begin from cuttings of a positively-identified holly variety. The cuttings are labeled either male or female based upon the gender of the parent plant.
It's possible to graft either a male or female branch onto an existing holly to produce berries, but you can't change the gender of a bush or a cutting. If you want to have only one holly, you could either purchase one of these special grafted hollies or one of the naturally self-fertile types such as the Burford holly (Ilex cornuta 'Burfordii').
Often a lone female holly will be successful in bearing fruit, thanks to one of the "wild-card" hollies, such as American holly (Ilex opaca), that are able to pollinate a number of different varieties. If you're pretty sure you have a female and you haven't seen any berries, consider planting a 'Jersey Knight' American holly (a male). There's obviously no guarantee, but on the upside, you'll be adding great cover for the birds and getting a good landscape plant.