Elderberries generally require pollination for fruit set.

Bob Gordon: the fruits of this Elderberry are sweeter and larger than other cultivars. Vigorous and productive, this cultivar can be mowed to the ground after dormancy and fruits can be harvested in the following year on primocane stems. It grows bending canes up to 8 feet tall. Harvest in July. Hardiness Zones 4-8. Optimal pollination from any variety.
 
Wyldewood is a variety with high vigor. Similarly to Bob Gordon, the plants can be mowed to the ground after dormancy as a method of pruning. The new primocane stems will yield fruits in the following year. Plants are productive with large cymes of fruit on bending canes 5 to 8 feet tall. Harvest in August. Hardiness Zones 3-8. Optimal pollination from Ranch.
 
Adams is a highly productive, semi self-fertile, and vigorous cultivar known for its highly aromatic flowers and larger fruits in clusters five inches in diameter. Upright canes, up to 8 feet tall. Harvest in mid-August. Hardiness Zones 4-9. Optimal pollination from Johns.
 
Johns is the highest yielding variety. The flavor of the berries is sweet with a hint of a dry, tangy flavor, which elderberries are known for. Plants will adapt to any soil type when adequately watered and will produce fruits the second year after planting. Upright canes, up to 10 feet tall. Harvest in mid-august. Hardiness Zones 3-8. Optimal pollination from Wild.
 
Ranch is the best choice for growing in extreme climates. The plants are short and easily harvested. The stems are strong and shorter in stature than other cultivars, growing to five to six feet tall. Clusters of fruits can be found in the middle of the stems to the top. The plants grow in most soil types and are the most tolerant to non-fertile soils. short, upright canes. Harvest in August. Hardiness Zones 3-8. Optimal pollination from Wyldewood.

Wild is considered to be the best all around pollinator due to its elonged blooming schedule: starts and ends after cultivated varieties. However, it has the least amount of blooms and thus the least amount of berries. The flavor profile of wild is indeterminate due to its variable nature, including size of the berries and bush. In terms of adaptability, it performs similarly to ranch in infertile or drought ridden soils. It tends to grow with bending canes up to 10 feet tall and harvested from August to September. Hardiness zones 4-8.

Disclaimer: berries should be ripe and cooked before eaten as some people have sensitivity to the alkaloids present. They are always poisonous when unripe.