Answer: The Blue Girl and Blue Boy are considered a fruiting pair, meaning they will bloom at the same time and so the male is a suitable pollen source for one or more females. The pollen is moved by flying insects, there is nothing you really need or can do to help it along. Heavy flowering will produce a heavy berry crop the next fall. Sometimes rain or windy weather can interfere, but otherwise there should be a berry for each flower on the female plant.
Pruning is probably the biggest culprit in reducing berry set. These plants need little or no pruning, their natural shape is quite symmetrical and even. There is no "good" time to prune because it will either reduce flowering (buds set on wood that grew the year before) or remove berries.
Another potential problem is winter damage, where cold or wind reduces flowering. You might use an antidessicant spray and/or erect a wind break for them if they are in a windy location.
Finally, allow them a few years to settle in and become established before you expect high performance. They will be using more energy for rooting than flowering at first.
I should mention that these plants will not do well in the house over the winter; they need to be colder than that. You could put them in a sheltered but cold location such as a garage. They should be as cold as possible without allowing the soil to freeze solid. Water as needed to keep the soil from going bone dry; plant them outside as soon as the ground can be worked in the spring.
Good luck with your hollies!
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