Rock Soapwort in Zone 5a & 5b
Saponaria ocymoides
Yes, rock soapwort grows in zones 5a and 5b and comes back each year. Plant it outside Apr 26–May 3.
When to plant rock soapwort in zone 5b
Zones 5a and 5b 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 26–May 3 |
| Estimated bloom | First real harvest the season after planting |
Spacing: about 2 square feet per plant (square-foot-gardening spacing). Mature height: 6-9 in.
Before you plant: Rock soapwort has a winter-hardiness note for zone 5b. See the details below.
Plant alongside it in zone 5b
These go outside within two weeks of rock soapwort in zone 5b, so one planting day can cover them.
- Agrostemma (Corn Cockle)Apr 26–May 3
- AstilbeApr 26–May 3
- Bachelor's Button (Cornflower)Apr 26–May 3
- Basket-of-GoldApr 26–May 3
- Bupleurum (Thoroughwax)Apr 26–May 3
- CalendulaApr 26–May 3
Rock soapwort is a trailing rock-garden perennial, and it is a different plant from the soapwort.
How rock soapwort fits zone 5's season
Zone 5b's frost-free window runs about 148 days, from May 10 to October 5. Rock soapwort 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.
Rock soapwort is hardy in zones 2-9, so in zone 5b it stays in the ground through winter and comes back rather than being replanted. Allow about 1.5 ft of spread at maturity.
Rock Soapwort planting windows in every zone
Zone 5b is highlighted. Useful for comparing against a neighbouring zone, or for a garden somewhere else.
| Zone | Start indoors | Sow or plant out | Bloom |
|---|---|---|---|
| 2a & 2b | Not usually | May 6–May 13 | First real harvest the season after planting |
| 3a & 3b | 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 (your zone) | 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 |
Zone 2 sows before zone 3 here, which looks wrong and is not. USDA zones rank winter cold, not season length, and zone 2 is mostly interior Alaska, where hard winters come with warm summers. More on what a zone measures.
Good companions
No well-established companions for rock soapwort.
Where to buy rock soapwort seeds
None of the seed suppliers we list carries rock soapwort 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 rock soapwort" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 5b calendar · Plan your beds in the Garden Designer →
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Growing Rock Soapwort in USDA zone 5b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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