Milk Thistle in Zone 6a & 6b
Silybum marianum
Yes, milk thistle grows in zones 6a and 6b. Plant it outside Apr 11–Apr 18.
When to plant milk thistle in zone 6b
Zones 6a and 6b 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 | Apr 11–Apr 18 |
| Estimated harvest | Aug 9–Aug 16 (~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 6b
These go outside within two weeks of milk thistle in zone 6b, so one planting day can cover them.
- DillApr 18–Apr 25
- BorageApr 25–May 2
- ChervilApr 11–Apr 18
- ChivesApr 11–Apr 18
- HorehoundApr 11–Apr 18
- ParsleyApr 11–Apr 18
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 6's season
Zone 6b's frost-free window runs about 173 days, from April 25 to October 15. Milk thistle needs about 120 days from sowing to first harvest.
Milk Thistle planting windows in every zone
Zone 6b 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 (your zone) | 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 | 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)
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Growing Milk Thistle in USDA zone 6b: when to start seeds indoors, when to direct-sow, and when to expect a harvest.
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