Milk Thistle in Zone 5a & 5b
Silybum marianum
When to plant milk thistle in zone 5b
Zones 5a and 5b share the same average frost dates in our data, so this page covers both.
Method: Direct sow: Direct-sow outside. Milk Thistle doesn't transplant well, or doesn't need the extra time indoors.
| Start indoors | Not typically started indoors |
|---|---|
| Direct sow / transplant outside | Apr 26–May 3 |
| Estimated harvest | Aug 24–Aug 31 (~120 days after direct-sowing) |
Spacing: about 4 square feet per plant (square-foot-gardening spacing). Mature height: 3-5 ft.
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 5's season
Zone 5b's frost-free window runs about 148 days, from May 10 to October 5. Milk Thistle needs about 120 days from sowing to first harvest.
Good companions
No standout companions recorded yet for Milk Thistle.
Where to buy 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 5b calendar · Full companion planting guide · Full plant profile · Plan your beds in the Garden Designer →
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Growing Milk Thistle in USDA zone 5b: when to start seeds indoors, when to direct-sow, and when to expect a harvest.
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