Butterfly Weed (Asclepias) in Zone 4a & 4b
Asclepias tuberosa
Yes, butterfly weed (asclepias) grows in zones 4a and 4b. Start seeds indoors Mar 20–Mar 27 and plant out May 22–May 29.
When to plant butterfly weed (asclepias) in zone 4b
Zones 4a and 4b share the same average frost dates, so this page covers both.
Method: Start indoors: Start indoors from seed, then transplant outside. It needs a head start most zones can't give it by direct-sowing alone.
| Start indoors | Mar 20–Mar 27 |
|---|---|
| Direct sow / transplant outside | May 22–May 29 |
| Estimated bloom | About a year after planting |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 1.5-3 ft.
Plant alongside it in zone 4b
These go outside within two weeks of butterfly weed (asclepias) in zone 4b, so one planting day can cover them.
- NasturtiumMay 22–May 29
- MarigoldMay 22–May 29
- Ageratum (Flossflower)May 22–May 29
- Annual Geranium (Pelargonium)May 22–May 29
- Campanula (Bellflower)May 22–May 29
- Castor BeanMay 22–May 29
Butterfly weed is a native perennial wildflower grown as much for feeding monarch butterfly caterpillars, one of the milkweeds they depend on, as for its own clusters of bright orange flowers.
How butterfly weed (asclepias) fits zone 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Butterfly weed (asclepias) takes about a year from planting to first bloom, so it spans more than one growing season.
Butterfly Weed (Asclepias) planting windows in every zone
Zone 4b is highlighted. Useful for comparing against a neighbouring zone, or for a garden somewhere else.
| Zone | Start indoors | Sow or plant out | Bloom |
|---|---|---|---|
| 3a & 3b | Apr 4–Apr 11 | Jun 6–Jun 13 | About a year after planting |
| 4a & 4b (your zone) | Mar 20–Mar 27 | May 22–May 29 | About a year after planting |
| 5a & 5b | Mar 15–Mar 22 | May 17–May 24 | About a year after planting |
| 6a & 6b | Feb 28–Mar 7 | May 2–May 9 | About a year after planting |
| 7a & 7b | Feb 13–Feb 20 | Apr 17–Apr 24 | About a year after planting |
| 8a & 8b | Jan 28–Feb 4 | Apr 1–Apr 8 | About a year after planting |
| 9a & 9b | Dec 21–Dec 28 | Feb 22–Mar 1 | About a year after planting |
Good companions
No well-established companions for butterfly weed (asclepias).
Where to buy butterfly weed seeds
None of the seed suppliers we list carries butterfly weed seeds right now. A local garden center or a specialty seed house is the place to look.
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing butterfly weed (asclepias)" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 4b calendar · Plan your beds in the Garden Designer →
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Growing Butterfly Weed (Asclepias) in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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