Mammoth sunflowers are towering annuals that can pass 3 m tall and carry huge seed-filled heads. Once established they are notably drought-tolerant and draw in pollinators.
See this plant in the collectionSoil pH
6.0 – 7.5
Germination soil temp
15 – 29 °C
Growing air temp
21 – 32 °C
Spacing
45 – 60 cm apart
Sowing depth
2.5 – 5 cm
Sun
6 – 8+ hours per day
Water
2.5 cm per week
Days to maturity
80 – 120
Sow directly outdoors after the last frost.
Pick a site sheltered from strong wind.
Stake plants in exposed positions.
Water deeply at the root zone rather than the stem.
Harvest heads when the back turns yellow-brown and bracts dry.
Every figure above comes from these pages.