Ageratum (Flossflower) in Zone 3a & 3b
Ageratum houstonianum
Yes, ageratum (flossflower) grows in zones 3a and 3b. Start seeds indoors Apr 11–Apr 18 and plant out Jun 6–Jun 13.
When to plant ageratum (flossflower) in zone 3b
Zones 3a and 3b 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 | Apr 11–Apr 18 |
|---|---|
| Direct sow / transplant outside | Jun 6–Jun 13 |
| Estimated bloom | Aug 20–Aug 27 (~75 days after transplanting) |
Spacing: 4 per square foot (square-foot-gardening spacing). Mature height: 1-2 ft.
Plant alongside it in zone 3b
These go outside within two weeks of ageratum (flossflower) in zone 3b, so one planting day can cover them.
- NasturtiumJun 6–Jun 13
- MarigoldJun 6–Jun 13
- Annual Geranium (Pelargonium)Jun 6–Jun 13
- Butterfly Weed (Asclepias)Jun 6–Jun 13
- Campanula (Bellflower)Jun 6–Jun 13
- Castor BeanJun 6–Jun 13
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 3's season
Zone 3b's frost-free window runs about 98 days, from May 30 to September 5. Ageratum (flossflower) needs about 75 days from transplant to first bloom.
Ageratum (Flossflower) 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 |
|---|---|---|---|
| 2a & 2b | Apr 1–Apr 8 | May 27–Jun 3 | Aug 10–Aug 17 |
| 3a & 3b (your zone) | 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 | 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 3b calendar · Plan your beds in the Garden Designer →
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Growing Ageratum (Flossflower) in USDA zone 3b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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