Common Name Centaurea, Silver-knapweed
Genus  Centaurea
Species C. ragusina
Family Asteraceae
Life Cycle  Annual (Perennial in zones 9-11)
Tray Size  32
Plug Care Harden off and plant out or bump up into larger pots soon after receiving plugs. When planting out be sure you to not bury the crowns. Plant the plugs so that the top of the growing medium is level with the soil.
Netting / Staking Not necessary.
Temperature Range Annual outside of zones 9-11, will thrive in the summer weather of all colder zones as an annual. 
Spacing 14-16"
Soil Preference Well drained, with a moderate organic content. Irrigate regularly but allow the soil to dry moderately between cycles. Overwatering will cause root rot. 
Day Length Day-neutral, plant in full sun. High light is extremely important for plant health. 
Pinching Do not pinch. 
When to Plant Plant in the spring after last frost has passed. Can be bumped up into larger pots and grown on in a heated greenhouse prior to last frost to achieve a larger size transplant. 
Harvesting This plant is grown for its beautiful silvery white foliage. Although not the tallest growing, the leaves hold up beautifully in floral creations and they will even withstand being completely out of water for hours without wilting. Harvest leaves close to the base of the plant when they are mature and leathery. 
Post Harvest Care For the longest vase life, cut stems(leaves) should be plunged into cool water and allowed to hydrate. When being used in arbors or installations they can go without water for hours and maintain hydration. 
Diseases / Insects No major pests or diseases to note. Bacterial leaf spot is possible in poorly draining soil or areas with high humidity and lack of airflow. 
Bailey's Notes Centaurea 'Snowy Owl' has not been extensively trialed as a cut foliage so we would love to hear back from growers with first hand experience.
Resources  Growing Centaurea