Growing Bupleurum (Thoroughwax): A Complete Profile
By Growing Home Greens Team · August 10, 2026
Bupleurum, also called thoroughwax, is a chartreuse-toned filler flower that reads more like foliage than bloom in a bouquet, useful for softening bolder cut flowers without pulling attention away from them.
Slow, cool germination
Transplant, starting seed 5 to 8 weeks before planting out, or direct-seed into cool soil at a quarter inch deep. Germination is slow and deliberate, taking 14 to 21 days at a cool 55-60°F, so give it the full window before assuming a tray has failed. Space plants 4 to 10 inches apart; mature stems reach 24 to 36 inches and can need support in a windy spot.
Two harvest points
For fresh arrangements, cut once the flower heads begin to show color. For dried arrangements, wait until the flowers are fully open, then hang to dry.
Bupleurum has no recorded companions or antagonists in our data. See the full companion guide for bupleurum for how it’s tracked. Its height makes it a good back-row filler in the Garden Designer, planted alongside bolder cut flowers it’s meant to complement rather than compete with.
Source: Bupleurum: Key Growing Information, Johnny’s Selected Seeds.
Companion planting guide for Bupleurum (Thoroughwax) · Find your planting dates
Typically viable in USDA zones 2-11. Not sure your zone? Look it up by ZIP code.
Method: Either: Start indoors for an earlier harvest, or direct-sow outside for less fuss. Bupleurum (Thoroughwax) tolerates either.
See exact start-indoors, direct-sow, and harvest dates for your zone →
How many Bupleurum (Thoroughwax) plants fit per square foot?
Spacing: 2 per square foot (square-foot-gardening spacing). Mature height: 2-3 ft.
Varieties worth considering
- Straight-species bupleurum (Bupleurum rotundifolium): Johnny's Selected Seeds sells this species plain; the chartreuse, foliage-like color is what growers are after, and there's no meaningful named-cultivar market beyond the species. (source)
Cited from the source shown next to each variety. We haven't grown these ourselves yet, so treat this as a research-backed starting point, not a personal endorsement.
Where to buy bupleurum seeds
As an Amazon Associate we earn from qualifying purchases. Some links on this page also go to other retailers we may earn a commission from as an affiliate, at no extra cost to you. We only recommend products with a genuine consensus of positive, independent reviews. See the sources cited on each item.
See it growing
Search YouTube for "growing bupleurum (thoroughwax)" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
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Growing Bupleurum (Thoroughwax): A greenish-yellow filler flower that reads more like foliage than bloom in a bouquet, useful for softening bolder cut flowers without competing with them.
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