Ageratum
Ageratum houstonianum
Also called floss flower
Ageratum is a frost-tender annual with fluffy blue, pink or white flower clusters that is usually started from seed indoors about 8 to 10 weeks before the last spring frost.
Quick facts
- Germination time
- 7–21 days
- Germination temperature
- 24–27 °C75–81 °F
- Sowing depth
- On the surface
- Spacing between plants
- Not yet verified
- Days to maturity
- Not yet verified
- Sun
- Full sun, partial shade
Safety for cats and dogs: not yet verified.
By SeedBattle EditorsUpdated
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01 · Overview
About ageratum
Ageratum (Ageratum houstonianum), also called floss flower, is a frost-tender annual. Its fluffy, aster-like flowers grow in clusters and are mostly blue, though pink and white forms exist. The plant grows in neat mounds, blooms from late spring through fall, and is one of the more dependable flowering annuals.
Growing details
- Start indoors
- 8–10 weeks before the last frost
- Sow outdoors
- Not yet verified
- Water
- Moderate
- Containers
- Yes
- Height
- 15–30 cm6–12 in
- Spread
- 25–30 cm10–12 in
- Frost tolerance
- Tender (no frost)
- Soil pH
- Not yet verified
- Life cycle
- Annual
Sowing timeline
When to sow ageratum seeds
Counted from your area's average last spring frost date. Find yours from a local weather service or garden center, then count back or forward.
- Germination time
- 7–21 days
- Germination temperature
- 24–27 °C75–81 °F
- Frost tolerance
- Tender (no frost)
02 · How to grow
How to grow ageratum from seed
Start seeds indoors about 8 to 10 weeks before the last expected spring frost. Do not cover the seed, because light helps it sprout. Seeds usually sprout in 7 to 21 days; one seed company gives 7 to 10 days at 75 to 80 °F (24 to 27 °C).
Transplant seedlings into trays or pots once they are large enough to handle. Harden them off and move them into the garden after all risk of frost has passed. Direct seeding outdoors is not recommended. Plant in a sunny spot. Spacing differs between guides: 6 to 8 inches (15 to 20 cm) apart, or 10 to 12 inches (25 to 30 cm) apart.
03 · Care
Caring for ageratum
Ageratum grows in full sun and can also take partial shade. It likes rich, moist, well-drained soil and tolerates dry conditions, and it is moderately drought tolerant. It needs fertile soil to keep blooming through summer.
Remove spent flowers to encourage more blooms. Most varieties keep brown flowerheads on the plant, so deadhead as needed to keep plants looking tidy.
At a glance
How ageratum compares with other flowers
Worked out from the growing facts of the 79 seeds in Flowers on SeedBattle.
- Ageratum
- Each of the other flowers
- Their average
- Germination timeSlower to sprout than average
7–21 days
Average for flowers: 12 days, from 42 other seeds
- Germination temperatureWarmer than average
24–27 °C75–81 °F
Average for flowers: 21 °C70 °F, from 40 other seeds
- Sowing depthShallower than average
On the surface
Average for flowers: 4 mm⅛ in, from 25 other seeds
- HeightShorter than average
15–30 cm6–12 in
Average for flowers: 71 cm2½ ft, from 68 other seeds
04 · Problems
Common ageratum problems
Ageratum is susceptible to powdery mildew. Spider mites can affect the plants, especially in hot, dry weather. Some cultivars show excellent resistance to phytophthora. Overall, serious insect or disease problems are not common.
05 · Harvest
Harvesting ageratum
Tall, upright varieties can be used as cut flowers. Taller varieties make good cut flowers.
Ageratum questions
How long do ageratum seeds take to germinate?
Germination usually takes 7 to 21 days. One seed company gives 7 to 10 days at 75 to 80 °F (24 to 27 °C).
When should I start ageratum seeds indoors?
Start them about 8 to 10 weeks before the last expected spring frost.
Can I grow ageratum in a pot?
Yes, it is good for beds and containers.
Does ageratum need full sun?
It grows best in full sun, with 6 or more hours of direct sunlight a day. It can also grow in partial shade.
Quick answers
More ageratum questions
Short answers taken from the growing facts on this page.
How deep should I sow ageratum seeds?
Sow them on the surface.
What temperature do ageratum seeds need to sprout?
Ageratum seeds germinate at 24–27 °C75–81 °F.
How tall does ageratum grow?
Ageratum grows 15–30 cm6–12 in tall.
Can ageratum survive frost?
No. Ageratum is tender, so it can't take frost.
Is ageratum an annual or a perennial?
Ageratum is an annual.
How much water does ageratum need?
Ageratum has moderate water needs.
Side by side
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