How to Grow Helianthus Plants in your Garden

Gardener's HQ Guide to Growing Sunflower, Jerusalem Artichoke, and Sunroot

Helianthus are a large genus of plants that can be grown as Hardy perennials or hardy annuals.

They are better known as sunflowers, and both sunflower oils and sunflower seeds are of great commercial and health value.

Most people associate Helianthus members with great height (between 1.5 to 3 metres), but some dwarf varieties that only reach 45 cm in height are available.

They carry large daisy like flowers, mainly of Yellow or orange, but sometimes cream, that flower from the middle of summer until the middle of autumn.

Sunflower Picture

Helianthus Plants are great to show off, and they can also be used as tall plants at the back of borders.

Helianthus annuus
Helianthus annuus – Annual Sunflower by TANAKA Juuyoh; creative commons.

Helianthus tuberosus
Helianthus tuberosus - Jerusalem artichoke by Blumenbiene; creative commons.

Helianthus Growing and Care Guide

Common Names: Sunflower, Jerusalem artichoke, Sunroot, Texas blueweed, Girasol. Sunflower: Common; Giant; Mammoth; Swamp; Prairie; Cusick's; Lakeside; Smooth; Longleaf; Maximillian.
Life Cycle: Hardy annual. Hardy perennial, half hardy perennial.
Height: 18 to 120 inches (45 to 300 cm).
Native: Mediterranean, Americas, Europe, Asia, Australasia, Africa.
Growing Region: Annuals: zones 1 to 10. Perennials: zones 3 to 10.
Flowers: Summer and autumn.
Flower Details: Yellow, orange, cream. Rays and discs. Flat heads.
Foliage: Some perennials have rosette leaves. Commonly sunflowers have a rough, hairy branched stem and sticky ovate leaves; these become narrower further up the stem.
Sow Outside: 1/4 inch (6mm). Following last frost. Spacing 12 to 40 inches (30 to 100 cm).
Sow Inside: Use peat pots. Germination time: one to three weeks. Temperature 70 to 80°F (21 to 27°C). Three weeks in advance. Transplant outdoors following the last frost.
Requirements: Full sunlight or light shade. Grows in most soils, best results in deep, rich soils of pH 5 to 7 that have good drainage. Provide support. Occasional light feed. Regular watering. Pinch tips. Cutback perennials to the ground in autumn. Propagate perennials by division in spring in cold areas or in autumn in warmer areas.
Family: Asteraceae.
Miscellaneous: The term Jerusalem artichoke comes from the Italian word for the plant: Girasole; turning to the sun.

How to Grow Sunflower (Helianthus) Plants

If growing Helianthemum outside then it is best to sow sunflower seeds outdoors at a depth of 6mm following the last frost of spring. Sunflowers like to grow in a sunny or partially shaded area that has good drainage. they can be grown in most soils but if you want to grow big sunflowers then use a soil that is of pH5 to 7, deep and rich.

You can start to grow sunflowers indoors first. When planting sunflower seed indoors sow them in peat pots about three weeks before the last frost of spring. They will take about 10 days to germinate at a temperature of 21 to 30 degrees centigrade. The sunflower seedlings should then be transplanted about a metre apart after the last frost of spring.

Caring for Sunflowers and other Helianthus in the Garden

Sunflower care is pretty easy; If you want to create bushy sunflowers then they should be pinched back when they are young to encourage branching. Due to their large heights it is important to stake sunflowers to protect them from windy conditions; especially if growing solitary. Helianthemum will require lots of watering but only feed them lightly to produce health flowers. Although sunflowers are pretty easy to look after, it is difficult to grow other plants around them as they carry toxins in their roots that act to give sunflowers a competitive advantage over other plants.

Harvesting sunflower seeds

If you require the sunflower seeds for culinary use, then they should be protected from birds during seed maturation, this can be done by placing a linen or cheese cloth over the head of the sunflower.

I hope that you enjoyed this guide on how to grow Helianthus plants. You may also enjoy the following Gardener's HQ growing guides: How to grow Golden Rod and Cotula plants.