Milk Thistle in Zone 9a & 9b
Silybum marianum
Yes, milk thistle grows in zones 9a and 9b. Plant it outside Feb 1–Feb 8.
When to plant milk thistle in zone 9b
Zones 9a and 9b share the same average frost dates, so this page covers both.
Method: Direct sow: Direct-sow outside. It doesn't transplant well, or doesn't need the extra time indoors.
| Start indoors | Not typically started indoors |
|---|---|
| Direct sow / transplant outside | Feb 1–Feb 8 |
| Estimated harvest | Jun 1–Jun 8 (~120 days after direct-sowing) |
Spacing: about 4 square feet per plant (square-foot-gardening spacing). Mature height: 3-5 ft.
Plant alongside it in zone 9b
These go outside within two weeks of milk thistle in zone 9b, so one planting day can cover them.
- DillFeb 8–Feb 15
- BorageFeb 15–Feb 22
- ChervilFeb 1–Feb 8
- ChivesFeb 1–Feb 8
- HorehoundFeb 1–Feb 8
- ParsleyFeb 1–Feb 8
Milk thistle is handsome, widely sold as a medicinal herb, and illegal to let grow in parts of the country.
How milk thistle fits zone 9's season
Zone 9b's frost-free window runs about 293 days, from February 15 to December 5. Milk thistle needs about 120 days from sowing to first harvest.
Milk Thistle planting windows in every zone
Zone 9b is highlighted. Useful for comparing against a neighbouring zone, or for a garden somewhere else.
| Zone | Start indoors | Sow or plant out | Harvest |
|---|---|---|---|
| 5a & 5b | Not usually | Apr 26–May 3 | Aug 24–Aug 31 |
| 6a & 6b | Not usually | Apr 11–Apr 18 | Aug 9–Aug 16 |
| 7a & 7b | Not usually | Mar 27–Apr 3 | Jul 25–Aug 1 |
| 8a & 8b | Not usually | Mar 11–Mar 18 | Jul 9–Jul 16 |
| 9a & 9b (your zone) | Not usually | Feb 1–Feb 8 | Jun 1–Jun 8 |
| 10a & 10b | Not usually | Jan 16–Jan 23 | May 16–May 23 |
Harvest dates are about 120 days after the sow or plant-out date.
Good companions
No well-established companions for milk thistle.
Where to buy milk thistle seeds
True Leaf Market (each supplier's milk thistle seeds)
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing milk thistle" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 9b calendar · Plan your beds in the Garden Designer →
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Growing Milk Thistle in USDA zone 9b: when to start seeds indoors, when to direct-sow, and when to expect a harvest.
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