Zone: 3 to 8
Soil: Sand to loam
Light: Full sun to part sun
Bloom colour: Mostly blue and pink
Bloom period: Early summer onwards
Height: 24 to 36 inches
Moisture: Dry to medium
Attracts: A variety of small bees, bumblebees and syrphid flies. It also attracts smaller butterflies.
Notes: I like Centaurea as a plant because it flowers early in the season and is popular with bees when many other garden plants are not in bloom. However, Centaurea is not native to Canada and can be invasive. Therefore, I recommend that gardeners only use this plant in highly managed gardens, where its distribution can be well controlled, or not at all. There are many native alternatives and they are listed below. I will no longer plant it.
These garden plants generally come from Europe where they grow on mountainsides or in sub-alpine slopes. Therefore, they adapt quite easily to garden conditions in North America.The most common species sold in Nurseries is Centaurea montana. The example shown here is a cultivar called "Amethyst in snow". They spread easily by stolons and tolerate poor soils. If they are cut back after the blooming period in May and June, they will flower again in August. Centaurea dealbata (Persian cornflower) is a taller species with pink flowers and pinnate looking leaves. It is the most attractive of the three species. A third species that is sometimes available is Centaurea macrocephala, which has strikingly stiff greenery topped with yellow thistle-like flowers. It flowers later than the other species mentioned and should be placed at the back of the border.
Alternatives to Centaurea include perennials such as Robin's plantain, Golden Alexanders, Penstemons, False indigo and Lupins; shrubs such as Viburnums, Dogwood or Shadbush; or flowering trees.