Astilbe in Zone 3a & 3b
Astilbe x arendsii
Yes, astilbe grows in zones 3a and 3b and comes back each year. Plant it outside May 16–May 23.
When to plant astilbe in zone 3b
Zones 3a and 3b 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 | May 16–May 23 |
| Estimated bloom | First real harvest the season after planting |
Spacing: about 2 square feet per plant (square-foot-gardening spacing). Mature height: 1.5-4.5 ft.
Before you plant: Astilbe has a winter-hardiness note for zone 3b. See the details below.
Plant alongside it in zone 3b
These go outside within two weeks of astilbe in zone 3b, so one planting day can cover them.
- Agrostemma (Corn Cockle)May 16–May 23
- Bachelor's Button (Cornflower)May 16–May 23
- Basket-of-GoldMay 16–May 23
- Bupleurum (Thoroughwax)May 16–May 23
- CalendulaMay 16–May 23
- California PoppyMay 16–May 23
Astilbe gives feathery plumes in shade, which is a rare combination. It asks for one thing in return and it does not negotiate.
How astilbe fits zone 3's season
Zone 3b's frost-free window runs about 98 days, from May 30 to September 5. Astilbe takes about 1 growing season to reach full flowering, so what matters here is how many of these seasons it gets, not whether one is long enough.
Astilbe is hardy in zones 3-9, so in zone 3b it stays in the ground through winter and comes back rather than being replanted. Allow about 1.5 ft of spread at maturity.
Astilbe planting windows in every zone
Zone 3b 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 (your zone) | Not usually | May 16–May 23 | First real harvest the season after planting |
| 4a & 4b | Not usually | May 1–May 8 | First real harvest the season after planting |
| 5a & 5b | Not usually | Apr 26–May 3 | First real harvest the season after planting |
| 6a & 6b | Not usually | Apr 11–Apr 18 | First real harvest the season after planting |
| 7a & 7b | Not usually | Mar 27–Apr 3 | First real harvest the season after planting |
| 8a & 8b | Not usually | Mar 11–Mar 18 | First real harvest the season after planting |
| 9a & 9b | Not usually | Feb 1–Feb 8 | First real harvest the season after planting |
Good companions
No well-established companions for astilbe.
Where to buy astilbe seeds
True Leaf Market (each supplier's astilbe seeds)
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See it growing
Search YouTube for "growing astilbe" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 3b calendar · Plan your beds in the Garden Designer →
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Growing Astilbe in USDA zone 3b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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