The spectacular Bolivian sunflower blossoms are up to 6 in (cm) in diameter and and have a light honeylike fragrance. Click here to download a large version of this image.
Bolivian sunflower is the towering big brother of the popular Mexican sunflower (T. rotundifolia Easily reaching up to 16 ft (5 m) tall and more than 12 ft (3.6 m) across, this sunflower makes a commanding statement. Bolivian sunflower has many branches and large coarse and hairy leaves that are oblong with marginal lobes and up to 14 in (35 cm) long. Bolivian sunflower grows fast and large during the spring and summer, then in autumn and winter it covers itself with hundreds of yellow-orange sunflowers, 3-6 in (7.5-15 cm) across. Each composite flower has 11-13 ray florets and 200-300 disc florets. All can give rise to seeds. The flowers smell like honey and are attractive to bees and butterflies. The seeds are small and can ride on the wind for several meters.
Location Tithonia diversifolia occurs naturally in Mexico and Central America. It has escaped cultivation and become established in tropical and subtropical areas throughout the world, including South Florida.
Culture Light: Sunflowers need full sun. Moisture: Although Bolivian sunflower does best in hot, dry climates and well drained soils, it still needs plenty of water. Hardiness: USDA Zones 9-11. Light frosts and freezes will kill Bolivian sunflowers to the ground, but if the damage isn't too bad, they come back in spring. Some people have had success with this tropical in Zone 8. In frost free climates, this sunflower can achieve the proportions of a small house. Propagation: The easiest way to start a new Bolivian sunflower is just to take a piece of stem, say 10 in (25 cm) long and an inch (2.5 cm) or so in diameter, and stick it in the ground. Don't water too much, and it should start producing roots and new leaves in a few days. You can also plant the seeds as soon as they ripen.
Jack grows this Bolivian sunflower in his Zone 8 garden where it succumbs to frost and freezes each winter and may or may not grow back from the roots in spring. Stem cuttings taken in fall and over-wintered indoors ensure Bolivian sunflowers for the following season.
Bolivian sunflower is an imposing shrub and is best suited to the larger landscape. It is a big, rangy plant and not inclined to be neat and tidy. Several of these fast growing biggies will make a great screen, and make it fast. Sometimes branches break off and may take root where they lie on the ground, thus speeding the development of the screen. Alternatively, place a Bolivian sunflower in back of the shrub border or all alone as a single specimen. When in bloom, Bolivian sunflower draws attention to itself. Dead-heading is recommended to prolong the flowering season, but you may need a bucket truck to reach the higher flowers. You can prune Bolivian sunflower back hard after blooming to keep it from overtaking the neighborhood.
Bolivian sunflower has various medicinal uses among herbalists in tropical America, southern Asia and Africa. It currently is being investigated for anti-malarial properties.
Unfortunately, I can't grow Bolivian sunflower in my yard because the squirrels and the deer eat them to the ground. The white-tailed deer eat the leaves, and the gray squirrels eat the stems. Even pieces of stem that I tried to start in nursery pots and hid behind the greenhouse were discovered and eaten by the squirrels. Researching this article, I learned that Tithonia diversifolia leaves and stems are particularly high in nutrients (especially N, P and K) and are used as fertilizer in tropical regions. I guess the squirrels already knew that.
In frost free areas Bolivian sunflower can spread and become an invasive nuisance. The species is still relatively new to North American gardeners and it has not yet been placed on Florida's invasive plant list. However, Bolivian sunflower has established in many areas of South Florida and reports are coming in that it is causing damage to native plants.