Ageratum (Flossflower) in Zone 9a & 9b
Ageratum houstonianum
Yes, ageratum (flossflower) grows in zones 9a and 9b. Start seeds indoors Dec 28–Jan 4 and plant out Feb 22–Mar 1.
When to plant ageratum (flossflower) in zone 9b
Zones 9a and 9b 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 | Dec 28–Jan 4 |
|---|---|
| Direct sow / transplant outside | Feb 22–Mar 1 |
| Estimated bloom | May 8–May 15 (~75 days after transplanting) |
Spacing: 4 per square foot (square-foot-gardening spacing). Mature height: 1-2 ft.
Plant alongside it in zone 9b
These go outside within two weeks of ageratum (flossflower) in zone 9b, so one planting day can cover them.
- NasturtiumFeb 22–Mar 1
- MarigoldFeb 22–Mar 1
- AmaryllisFeb 22–Mar 1
- Annual Geranium (Pelargonium)Feb 22–Mar 1
- Butterfly Weed (Asclepias)Feb 22–Mar 1
- Calla LilyFeb 22–Mar 1
Ageratum, also known as flossflower or blue mink, is a fuzzy-textured filler flower that's a classic choice for the back of a bed or a mass planting, needing no pinching or staking along the way.
How ageratum (flossflower) fits zone 9's season
Zone 9b's frost-free window runs about 293 days, from February 15 to December 5. Ageratum (flossflower) needs about 75 days from transplant to first bloom.
Ageratum (Flossflower) planting windows in every zone
Zone 9b 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 | Apr 1–Apr 8 | May 27–Jun 3 | Aug 10–Aug 17 |
| 3a & 3b | Apr 11–Apr 18 | Jun 6–Jun 13 | Aug 20–Aug 27 |
| 4a & 4b | Mar 27–Apr 3 | May 22–May 29 | Aug 5–Aug 12 |
| 5a & 5b | Mar 22–Mar 29 | May 17–May 24 | Jul 31–Aug 7 |
| 6a & 6b | Mar 7–Mar 14 | May 2–May 9 | Jul 16–Jul 23 |
| 7a & 7b | Feb 20–Feb 27 | Apr 17–Apr 24 | Jul 1–Jul 8 |
| 8a & 8b | Feb 4–Feb 11 | Apr 1–Apr 8 | Jun 15–Jun 22 |
| 9a & 9b (your zone) | Dec 28–Jan 4 | Feb 22–Mar 1 | May 8–May 15 |
| 10a & 10b | Dec 12–Dec 19 | Feb 6–Feb 13 | Apr 22–Apr 29 |
| 11a & 11b | Nov 13–Nov 20 | Jan 8–Jan 15 | Mar 24–Mar 31 |
Bloom dates are about 75 days after the sow or plant-out date, not after starting seeds indoors.
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 ageratum (flossflower).
Where to buy ageratum seeds
Botanical Interests · True Leaf Market (each supplier's ageratum seeds)
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing ageratum (flossflower)" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 9b calendar · Plan your beds in the Garden Designer →
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Growing Ageratum (Flossflower) in USDA zone 9b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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