Growing Ageratum (Flossflower): A Complete Profile
By Growing Home Greens Team · August 10, 2026
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.
Transplant only
Direct-seeding isn’t recommended for this one; it needs the controlled start of an indoor sowing. Sow seed 6 to 8 weeks before planting out, and don’t cover it, since light aids germination. Bottom-water or mist rather than watering overhead, which can displace soil onto the seed. Germination takes 7 to 10 days at 75-80°F. Space plants 9 to 12 inches apart after the danger of frost has passed.
Tolerant of part shade
Full sun is ideal, but ageratum tolerates part shade reasonably well where summers run hot, more forgiving than a lot of full-sun annuals if the planting spot isn’t perfectly sunny all day.
Harvest
Cut fresh once flower spikes are about three-quarters open. For drying, wait until flowers are completely open, then hang; be aware the flower color often fades once dried.
Ageratum has no well-established companion pairings, and nothing it needs to be kept away from. At 4 plants per square foot, it’s a low-maintenance filler for the Garden Designer, useful in mass plantings or as a border edge that doesn’t need staking.
Source: Ageratum: Key Growing Information, Johnny’s Selected Seeds.
Companion planting guide for Ageratum (Flossflower) · Find your planting dates
Typically viable in USDA zones 2-11. Not sure your zone? Look it up by ZIP code.
Mature height: 1-2 ft
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.
When to plant ageratum (flossflower), by zone
Every zone ageratum (flossflower) grows in. Pick your zone in the header and it will be highlighted here. Each zone links to its full page.
| 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 | 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.
See exact start-indoors, direct-sow, and harvest dates for your zone →
How many Ageratum (Flossflower) plants fit per square foot?
Spacing: 4 per square foot (square-foot-gardening spacing). Mature height: 1-2 ft.
Varieties worth considering
- 'Tall Blue Planet' (F1) ageratum (best for: cut-flower height): Johnny's Selected Seeds describes this as tall and upright with sturdy stems, a classic filler flower bred for cutting rather than the low bedding types. (source)
- 'Timeless Mix' ageratum (best for: mixed color filler): Johnny's Selected Seeds lists this as a classic filler in harmonious colors, a mixed-color alternative to the single-color Tall Blue Planet above. (source)
Why each variety is listed comes from the source shown next to it. We haven't grown these ourselves yet, so treat this as a research-backed starting point, not a personal endorsement. The buy links are separate from those sources: they go to seed suppliers that sell that exact variety, and we may earn a commission on some of them.
Where to buy ageratum seeds
Botanical Interests · True Leaf Market (each supplier's ageratum seeds)
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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)
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Growing Ageratum (Flossflower): A fuzzy-textured filler flower classic for the back of a bed or a mass planting, needing no pinching or staking to perform well.
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