Common Name Thoroughwax, Hare's Ear, Hound's Ear, Green Gold
Genus  Bupleurum 
Species B. rotundifolium 
Family Apiaceae
Life Cycle  Hardy Annual 
Tray Size  210
Plug Care Plant soon after arrival - do not allow to become rootbound and do not expose to any stressful conditions (heat, drought) or premature flowering may be triggered. Be gentle when transplanting as this species does not appreciate root disturbances. 
Netting / Staking One to two layers of netting can be beneficial.
Temperature Range Can tolerate light frost but in the field, should be protected from heavy frosts. Prefers cooler temperatures and will usually die off in the heat of summer. 
Spacing  8-12"
Soil Preference Tolerant of most soils, will grow best in loose, well  draining soil with a neutral pH and average fertility. 
Day Length Facultative long day. Can initiate flower buds at any day length, but usually stays vegetative during short days and elongates during the longer days of spring. 
Pinching Do not pinch. 
When to Plant

Plant plugs in the fall and overwinter for early season blooms the following year. Plant plugs in early spring for blooms in early summer.

You can plant multiple successions in areas with cooler summers to extend the bloom window. Plan to protect young plants with frost cloth if temperature drop below freezing.

Harvesting Expect the first flowers as little as 6-7 weeks following a spring planting. Harvest is entirely dependent on planting time and temperature. Harvest when the flowers are fully open, otherwise the cut stems will wilt.
Post Harvest Care Place cut stems immediately into cool water. Can be stored in the cooler for a short time - expect a vase life of 7-10 days. 
Diseases / Insects Typically robust and problem free. 
Bailey's Notes

If left to go to seed in the field they will readily self-sow. Watch for seedlings in the fall and/or early spring which will typically flower the year after you planted the initial plugs. 

For ease of harvesting, some growers will cut the entire plant as one stem. If you choose to cut only the main stem and leave some plant material behind, side branches may develop but they will be short. 

Resources Bupleurum rotundifolium, North Carolina Extension Gardener Plant Toolbox