Rock Soapwort in Zone 8a & 8b
Saponaria ocymoides
Yes, rock soapwort grows in zones 8a and 8b and comes back each year. Plant it outside Mar 11–Mar 18.
When to plant rock soapwort in zone 8b
Zones 8a and 8b 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 | Mar 11–Mar 18 |
| 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 8b. See the details below.
Plant alongside it in zone 8b
These go outside within two weeks of rock soapwort in zone 8b, so one planting day can cover them.
- Agrostemma (Corn Cockle)Mar 11–Mar 18
- AstilbeMar 11–Mar 18
- Bachelor's Button (Cornflower)Mar 11–Mar 18
- Bupleurum (Thoroughwax)Mar 11–Mar 18
- CalendulaMar 11–Mar 18
- California PoppyMar 11–Mar 18
Rock soapwort is a trailing rock-garden perennial, and it is a different plant from the soapwort.
How rock soapwort fits zone 8's season
Zone 8b's frost-free window runs about 230 days, from March 25 to November 10. 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 8b 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 8b 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 | 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 (your zone) | 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 8b calendar · Plan your beds in the Garden Designer →
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Growing Rock Soapwort in USDA zone 8b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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