Helianthus sp. (Sunflower)

Zone: 4 to 9

Soil: sand to clay

Light: Full sun to part sun

Bloom colour: Yellow

Bloom period: August to October

Height: 1 to 10 feet

Moisture: Usually dry to medium

Attracts: A variety of bees, butterflies, birds and small mammals.

Notes: Sunflowers are truly excellent plants for wildlife. The flowers are highly attractive to bees and the seeds that develop will attract finches and many other birds. They also flower for a long time starting in August.

It is best to give sunflowers their own space in the garden because the members of this genus have aggressive root systems and release chemicals that may affect the growth of other plants. This is an adaptation that helps them compete with other plants, so it is not a bad thing. However, you may find it helpful to contain the roots with barriers to prevent the plants from spreading too much.

Inspired by the paintings of Van Gogh, we mostly imagine annual sunflowers; however, there are over fifty species in N. America and nearly all of them are perennial. They are incredibly easy to grow and are one of the essential plants in a late summer or fall garden.

Annual sunflower is native to western parts of North America and is one of the best annuals to attract wildlife. It is a great plant to get kids interested in gardening. Choose a variety that is not pollen free because they are more attractive to wildlife and your children will see the seeds develop thereby learning about the plant reproduction cycle. The varieties with extra large flowerheads often need staking and do not look that great in the garden. There are dwarf varieties available that are only two feet high. These are more suitable for young children. Put them in pots with good soil and keep the soil moist. When the plant starts to wither, remove the flowerheads and let the seeds continue to develop. When you can see the seeds, hang them up for the birds.

Helianthus giganteus grows up to 10 feet high in part-shade in average or moist soil. In more sun and with more moisture, it can exceed 13 feet (4 m) and is one of the tallest perennials in North America. If you find your plants to be too tall, then consider a pruning in late June because the flower blooms are beautiful. While all sunflowers are spreaders, H. giganteus is the easiest of the species to control.

'Lemon Queen' is a manageable infertile hybrid. It has the advantage over the native species in that it is not an aggressive spreader and has a long bloom time. This cultivar grows up to seven feet high and flowers for months. It would make a great addition to any flower garden that peaks towards the end of the season. Being infertile, it does not produce seed, so it attracts only pollinators and not birds. In September, these plants are covered with bumblebees.

Most sunflowers need a good deal of sunshine to do well. Helianthus strumosus (pale-leaved sunflower) flowers in part-sun or under open indirect light. You can therefore plant this species on the north side of a building. It is one of the more delicate looking sunflowers and it often only grows four to five feet high. Another sunflower that handles shade well is Helianthus divaricatus. It also only grows up to five feet house. It is a fabulous plant to boost the colour of your shade beds in the fall, but it will spread quickly if the growing conditions are too good, so be prepared to install barriers. It only grows to about five feet high. H. divaricatus (woodland sunflower) is one of the easiest sunflowers to identify because the leaves are sessile.

Helianthus mollis is not native to Ontario but it is near native and already has naturalised. It comes from the Midwest and grows up to 6 feet high. It has a beautiful grayish-green foliage caused by a layer of hairs. Each flowerhead has a double layer of infertile ray flowers that makes these blooms particularly attractive. The foliage and flowers are together stunning. It is my firm favourite. It needs sand and quite dry soil to look its best. It can grow in clay too but it will be much shorter.

H. pauciflorus also has beautiful flowers with reddish centres but it is really a species that should be planted in larger areas as it spreads rapidly through rhizomes. In dry and sandy areas, it will only be about 2 feet high. If given more moisture, it gets to about 6 feet high.

Many gardeners are interested in H. tuberosus because it is a perennial sunflower with potential to produce food; however, when it comes to sunflowers, it is the thug of thugs. Plant it somewhere out of the way and on its own. You probably will not need to water it unless there is a drought. There is a lot of room for weeds to grow between the stalks, but it hardly ever needs weeding. Presumably it is really allelopathic. It grows up to 9 feet tall with large course leaves and the spectacular flowers are 3 inches across. Barriers are essential for this sunflower, but they will not stop the roots entirely. To get fat tubers that you can harvest, this plant needs to get plenty of sunshine. It can grow and flower profusely with just a few hours of sunshine, but the tubers will be too small.

Species native to Ontario include: Helianthus petiolaris; Helianthus decapetalus; Helianthus divaricatus; Helianthus giganteus; Helianthus nuttallii; Helianthus pauciflorus;Helianthus strumosus; Helianthus tuberosus;

Helianthus annuus - Annual sunflower
Helianthus giganteus
Helianthus giganteus - Tall sunflower
Helianthus 'Lemon Queen"
Helianthus strumosus
Helianthus tuberosus has wide toothed leaves and this is a good way to distinguish it from other sunflowers.
Helianthus strumosus
Helianthus strumosus is highly variable in its appearance and is easily confused with H. tuberosus.
Helianthus divaricatus
The leaves of Helianthus divaricatus are stalkless.
Helianthus mollis
Helianthus mollis
Helianthus pauciflorus
Helianthus petiolaris is a near native from the Midwest that has been introduced into Ontario. With climate change, this plant is going to be counted as a native plant in the next 20 years.  
Helianthus tuberosus
Helianthus tuberosus