Zone: 4 to 8
Soil: Sand to clay
Light: Full sun to part sun
Bloom colour: Lilac, purple, blue
Bloom period: Varies, see notes
Height: 1 to 3 feet
Moisture: Dry to medium
Notes: There is nearly always an ornamental onion available in a nursery, however, they are not typically native species. Usually, they are bulbs that flower early on in the season when there are few bees around that will take advantage. Giant onions can actually grow up to five feet tall. Typically the leaves will die back soon after flowering just like other spring bulbs. Compared to the species mentioned below, giant onions are of low value to wildlife.
Chives, which have naturalised in North America, are one of the most attractive plants to pollinators in June when they are in flower. A wide range of bees and some skippers visit the flowers to feed from the accessible nectaries. Of course, they are commonly planted for the flavours that they can provide when cooking. It is simply a nice coincidence that they have wildlife value and make great garden plants. They grow about 18 inches high and about 18 inches across. If you are unable to obtain a native onion, put some chives in your garden. They do well in full sun and tolerate dry conditions quite well in well drained soils. If chives are in your garden bed consider supporting them with a small trellis as they tend to get flattened in heavy rain. Do not put chives in unmanaged areas as they spread quite easily.
Round-headed leeks have long thin leaves with round balls of deep purple flowers that appear in the early part of summer. They too are popular with bees. While they are certainly beautiful, these plants spread too easily and they are not native.
None of the onions mentioned so far are native to North America. They are all from the old world flora. It is a shame that our native onions are hard to find in regular nurseries because they also have ornamental value. Nodding Wild Onion is an excellent plant to attract bees. Since its flowers hang upside-down, the plant is mostly pollinated by bumblebees. The plant naturally occurs in short-grass meadows, but does well in garden conditions. Plant it en masse to get the best ornamental effect. It grows about 12 - 18 inches high and will flower for about four weeks during mid-summer. Since the plant tolerates a range of conditions, it is almost impossible not to have some success with this plant.