How to Grow Ageratum
Ageratum houstonianum
When to Start
Sow indoors 4 weeks before last frost, or direct sow outdoors after frost risk has passed and soil reaches 15°C.
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Growth Stages
Approximate days from start
Care Essentials
- Apply a balanced liquid feed every 2–3 weeks during the growing season. Avoid high-nitrogen feeds which promote foliage over flowers.
- Compact mounding bedding plant, 15–30 cm tall. Flowers attract hoverflies and parasitic wasps. Excellent companion plant — deters whitefly from nearby vegetables. Frost-tender; plant out only after last frost.
Companion Planting
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Growing Conditions
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- Sow indoors
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- Transplant out
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- First harvest
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Spacing & Planting
| Plant spacing | 20 cm |
| Row spacing | 25 cm |
| Sow depth | 0 cm |
| Mature height | 30 cm |
| Mature spread | 25 cm |
Care Guide
- Feeding
- Apply a balanced liquid feed every 2–3 weeks during the growing season. Avoid high-nitrogen feeds which promote foliage over flowers.
- Watch for
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- Aphids on young shoots and flower buds
- Whitefly under leaves
- Powdery mildew in dry conditions
- Grey mould in wet or humid weather
Pests & Diseases
Pest Aphids
Identification: Clusters of small soft-bodied insects on shoot tips and flower buds. Sticky honeydew residue and distorted growth.
- Blast off with a strong jet of water
- Encourage ladybirds, lacewings, and hoverflies
- Apply insecticidal soap or neem oil spray
- Remove heavily infested shoots
- Pyrethrum-based contact spray as a last resort
Pest Whitefly
Identification: Tiny white winged insects under leaves that fly up when disturbed. Sticky honeydew and sooty mould on upper leaf surfaces.
- Yellow sticky traps to monitor and reduce populations
- Encourage natural predators (parasitic wasps, hoverflies)
- Apply insecticidal soap or neem oil to undersides of leaves
- Ageratum itself deters whitefly from nearby vegetables
- Pyrethrum spray targeting leaf undersides
Disease Powdery Mildew Golovinomyces cichoracearum
Symptoms: White powdery coating on leaves and stems. Leaves yellow and become distorted. Reduced vigour and flower production.
Treatment: Remove badly affected leaves. Improve air circulation. Apply a potassium bicarbonate or sulphur-based fungicide if severe.
Prevention: Space plants well for airflow. Avoid drought stress. Water at the base, not overhead.
Disease Grey Mould Botrytis cinerea
Symptoms: Grey fuzzy mould on flowers, stems, and leaves. Affected tissue collapses and rots. Spreads rapidly in cool, humid conditions.
Treatment: Remove and dispose of affected plant material immediately. Improve air circulation. Avoid overhead watering.
Prevention: Space plants well. Deadhead promptly. Avoid wetting foliage. Do not overwater.
Growing Conditions
| Min. soil temperature | 15°C |
| Germination temperature | 20–24°C |
| Base growth temperature | 10°C |
| Photoperiod sensitivity | day neutral |
Frequently Asked Questions
- How far apart should I plant Ageratum?
- Plant Ageratum 20cm apart with 25cm between rows.
- When does Ageratum flower?
- Ageratum typically flowers approximately 40 days after transplanting.
- Is Ageratum frost hardy?
- Ageratum is classified as Half Hardy.
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