I planted three staghorn sumacs several years ago. They have done well, and have nice fall color, but I was hoping to see the flowers and fruit. This summer, for the first time, there are flowers on one shrub. What prompted the change? Will the flowering plant have fruit?
Anecdotally, there are reports of Rhus typhina (staghorn or velvet sumac) taking a while to flower and fruit. If you don’t have flowers on more than one of your three plants, you are not likely to get fruit (unless your flowering plant is female and someone nearby has a male, in case your other two are also female). Rhus typhina and Rhus glabra (smooth sumac) are dioecious, meaning that they produce male and female flowers (yellow green upright cone-shaped panicles) on separate plants. Plants of both sexes need to be grown together, and pollen from the male flowers needs to reach the female flowers, for the the upright clusters of the fuzzy disc-shaped dark red fruit (berry-like drupes) to develop on the female plants. These fruit clusters are colloquially referred to as ‘bobs.’
You can examine the flowers on your plant closely (with a hand lens) to determine if they are male or female. Male flowers tend to be larger and have five yellow-tipped stamens, while female flowers have a three-lobed style in the center, and a calyx with five pointed lobes nearly the same length as the petals. Both flower stalks and calyx are densely hairy. [Source: Minnesota Wild Flowers field guide online] Here are additional photos to clarify the description.