Depending on the variety, sunflowers can range in height from 50cm to 3m.
Flowers and foliage
Generally tall hairy large leaved annuals producing large showy daisy like flowers in colours ranging from yellow orange and gold to mahogany red.
Prefers average moist well-drained soil in full sun. Tolerates poor soils that are on the dry side. Needs shelter from strong winds.
Preparation for planting
Bedding plants are usually raised from seed sown under trays. The seedlings can then be transplanted into small containers for growing before finally being planted out. Transfer seedlings outdoors to be hardened off before planting. The soil should be light and friable. Prior to planting, rake general-purpose fertiliser into the soil at about 100 grams (about 2 handfuls) per square metre. Plant at the same depth at which the plants were growing in their container; planting too deeply usually results in failure. Handle carefully to minimise root disturbance. If a bushy growing habit is desired, remove the growing tips from the seedlings when planting. Larger varieties often need staking, particularly if grown in exposed locations.
It is advisable to annually apply lime and add organic matter such as compost to the soil every second year. Remove spent blooms regularly to prolong the flowering season. Plant foliage often depreciates as the summer progresses. Removal of browned and tattered plants from the garden may improve the appearance of the landscape, but is a great disappointment to local bird populations that love to feed on the seeds. If the plants must come down, consider saving the seed heads for feeding the birds in winter. Harvest seed from favourite plants for use the following year (however, some cultivars will not reliably come true from seed).
Ecological and biodiversity benefits
Sunflowers attract beneficial insects to the garden and birds love to feed on the seeds once ripe.
Pests and diseases
Rust leaf fungal spots and powdery mildew are somewhat common. Caterpillars and beetles often chew on the foliage. Larger varieties often need staking particularly if grown in exposed locations.
Location at Auckland Botanic Gardens
Interesting facts and tips
Helianthus annuus are native to dry plains prairies meadows and foothills in the western US, Canada and northern Mexico. Sunflowers have become very popular commercial cut flowers throughout the world. Cultivated varieties are also commercially grown for their edible seeds which are used in Australia in livestock feed as birdseed and for cooking oils. Flower heads tend to follow the path of the sun each day from morning to night hence their common name.