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 recorded companions or antagonists in our data. See the full companion guide for ageratum for how it’s tracked. 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.

Method: Start indoors: Start indoors from seed, then transplant outside. Ageratum (Flossflower) needs a head start most zones can't give it by direct-sowing alone.

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)

Cited from the source shown next to each variety. We haven't grown these ourselves yet, so treat this as a research-backed starting point, not a personal endorsement.

Where to buy ageratum seeds

As an Amazon Associate we earn from qualifying purchases. Some links on this page also go to other retailers we may earn a commission from as an affiliate, at no extra cost to you. We only recommend products with a genuine consensus of positive, independent reviews. See the sources cited on each item.

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)

Pin this for later

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.

Save to Pinterest