Gomphocarpus fruticosus ‘Cottonbush’, also known as narrow-leaved cotton bush, swan plant or milkweed, is an unusual tender perennial grown primarily for its distinctive inflated seed pods. The softly spined, pointed pods begin pale green before developing attractive bronze and brown tones, bringing exceptional shape, texture and movement to fresh or dried floral arrangements.
Slender stems carry narrow foliage and small cream-white flowers before the ornamental pods form. Grow it as a half-hardy annual in the UK, choosing a warm, sunny position with free-draining soil. Plants tolerate heat and drier conditions once established, making this an intriguing choice for cutting gardens, contemporary borders and wildlife-friendly planting.
When to Sow: February – April
HOW TO SOW:
Soak the seeds in warm water for 24 hours before sowing.
Surface sow onto moist, free-draining seed compost and press the seeds gently into the surface. Do not cover, as light is required for germination. Keep at 20–23°C and maintain even moisture without saturating the compost. Germination usually takes 7–14 days.
Remove any cover as soon as seedlings appear to improve air circulation. Water carefully from below and transplant young seedlings into individual pots while they are still small, as the developing taproot dislikes disturbance. Grow on in bright, frost-free conditions. Harden off gradually and plant outside after all danger of frost has passed.
Classification: Tender Perennial, (usually grown as a Half-Hardy Annual in the UK)
Expert Level: Requires Some Experience
Germination Time: 7–14 Days
Site: Full Sun
Soil Type: Light, sandy or loamy, well-drained soil
Soil Acidity: All Types
Moisture: Moderately moist but well-drained; drought tolerant once established
Care: Protect from frost and avoid cold, waterlogged soil. Water regularly while plants establish, then allow the soil surface to dry slightly between waterings. Pinch out the growing tip to encourage branching and additional pod-bearing stems. Stake plants if required in exposed positions. The plant develops a deep root system and should not be moved once established. Wear gloves when handling cut or damaged stems, as the milky sap can irritate the skin and eyes and is toxic if ingested.
Use: Cut Flower Gardens, Dried Flower Gardens, Contemporary Borders, Wildlife Gardens and Floral Arrangements
Harvesting: Cut stems once the inflated pods are full-sized and firm but before they begin to split and release their seeds. Harvest during the coolest part of the day and place the stems immediately into clean water. Remove lower foliage and wear gloves to avoid contact with the milky sap. Stems may also be hung upside down in a warm, airy place for dried arrangements.
Days to Maturity: Approximately 105–130 Days
Flowering Time: June – September
Height: Approximately 90 cm
Plant Spacing: 45–60 cm