Answer: In order to have berries, you need to have several things happen. The plants need to set buds. They need to bloom simultaneously (both male and female) and the pollen needs to be transported by flying insects. Then the berries develop slowly where there were fertilized female blooms and eventually ripen in the fall.
There are several things that can interfere with this process. The most common one is pruning. Pruning will either remove the flower buds (these plants bloom on old wood from the year before), remove the flowers or immature fruit, or remove the maturing berries. Another one is bad weather during the bloom period. If rain or pesticide application for example interferes with the insects, there may be a reduced or no crop even though there were blooms. Next is overall health of the plants. If stressed, they will produce fewer buds, will bloom poorly or will drop immature berries. Summer heat and summer moisture stress for example can both do this; a late frost can sometimes damage the buds. Winter damage can also limit blooming, but that does not sound like it happened here. Overfertilizing can contribute to reduced bloom; the plants will be pushed to grow vegetatively and this occurs at the expense of blooming. LAck of sun can cause reduced blooming and fruiting as well -- although shade tolerant, these plants are really sun lovers. Last but not least, depending on the weather and microclimate hollies will bloom in late spring to early summer -- if they have buds, perhaps they just have not bloomed yet?
New plants are still be spending their energy rooting and so will bloom sparsely at first. Young plants tend to devote more energy to growing rather than fruiting, the display improves as the plants become established and mature.
I would suspect they did not bloom last year because they had been pruned prior to purchase to promote bushiness. As to this year, I can't tell you specifically but I hope this helps you trouble shoot. If none of the above seem plausible you might want to check with your local professionally trained and certified nurseryman and see if they have any suggestions. I hope you get a good crop next year!
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