Hi, Well it could be due to a number of issues. First, it depends on the age of the plants. They need to be mature enough to develop pollen and then berries. If these are relatively young plants or new transplants they may need some time before they produce berries. Also, it depends on how much sun they are receiving. You say they are on the north side of your house, but don't say how many hours of sun they are receiving. For best berry production, hollies require at least 6 to 8 hours of direct sunlight a day. And, finally, if your male holly flowers, but you get no berries on your female it's probably due to lack of pollinators such as bees and insects. You may want to help nature along by using an artist's paintbrush to move pollen from the male to the female.