Mexican sunflower, Tithonia rotundifolia

Overview of Mexican Sunflower

The genus Tithonia is in the daisy family (Asteraceae), and it includes 10 to 15 species of bushy annuals, perennials and shrubs native to Mexico and Central America. All have large, brightly colored daisy-like flowers on thick stems. Mexican sunflower, T. rotundifolia, is a vigorous, drought tolerant, warm season annual that is easy to grow in the ornamental garden. Other common names include red sunflower or just tithonia.

Tithonia plants grow 4 to 6+ feet tall with a large central stalk and a somewhat gangly, branching habit. The stems can be brittle. The dark green leaves are ovate to deltoid (triangular) in shape with serrate to crenate margins. The coarse leaves are usually entire but occasionally will be three lobed. The foliage and stems are covered with a soft downy fuzz, and the underside of the leaves are hairy.

The foliage of Mexican sunflower is coarse and hairy (L); the ovoid to deltoid leaves have serrate margins and are usually entire (C) but may be three lobed (R).

Flowers are produced from mid-summer until frost. The solitary flowers are borne on fragile hollow peduncles (flower stems) that are susceptible to being bent and are often broken by birds. Each 3-inch blossom has a number of bright red to orange ray flowers surrounding the central yellow disk flowers.

Thick, fuzzy buds (L) open (LC) to reveal bright red to orange ray flowers (C) surrounding yellow disk flowers (RC) that remain for a while after the ray flowers fall off (R).

The flowers are attractive to a wide variety of bees, butterflies and hummingbirds, and they can be used as cut flowers. Deadheading spent flowers will prolong blooming. The flowers are followed by grey to black flattened triangular seeds that are easy to collect to save to grow in subsequent years.

Many pollinators visit tithonia flowers including (L-R) bumblebee, longhorned bee, another wild bee, syrphid fly, monarch butterfly and tiger swallowtail.

Use tithonia at the back of borders and beds as a backdrop for shorter plants.

Landscape Use of Mexican Sunflower

Because of its tall stature, rangy habit and somewhat coarse texture, tithonia is best situated at the back of borders and beds to form a backdrop for shorter plants. It can also be used as a seasonal screen (especially if grown from transplants started early in the season). Use in mixed or annual borders with tall zinnia, coreopsis, and other flowers in hot colors for a high-energy planting, or tone down the brilliant orange-red flowers by combining with purple flowers and larger plants with dark-colored foliage, such as ornamental millet or castor bean or in mixed beds with woody plants such as smokebush or ‘Diabolo’ eastern ninebark.

General Care of Mexican Sunflower

Tithonia grows best in full sun in poor to average, well-drained soil. Avoid planting in rich soil or heavy fertilization that with promote excess foliage and weak stems. Pinch back plants to encourage bushier growth. Sturdier plants are less likely to fall over but plants often need to be staked to remain upright. Shelter plants from strong winds if possible. It has few pest problems and is not favored by deer.

Tithonia does best in full sun in well-drained soil.

Plant in the garden about two feet apart to provide support for adjacent plants, or place staked plants 3-4 feet apart. Since the plants tall with brittle stems, try to provide shelter from strong winds, but even in areas that are not windy these plants benefit from staking. It needs warm sunny weather to grow well so may not do much early in the season. In cool summers, late-planted direct-seeded plants may not bloom.

Plants can be sheared back in early summer by about a third to promote branching and reduce overall height somewhat.

Propagation of Mexican Sunflower

Grow tithonia from seed, either planted directly in the garden after the last spring frost date or started indoors 6-8 weeks before the average last spring frost date for earlier blooms. Sow shallowly as as light is beneficial for germination.

Cultivars of Mexican Sunflower

Only a few cultivars are generally available:

‘Fiesta del Sol’ – is a compact cultivar that grows only about 3 feet tall. It received an All-America Selections (AAS) award in 2000.
‘Goldfinger’ – is a relatively short variety (3-4 feet tall) with orange flowers.
‘Torch’ – is the most commonly offered cultivar, winning an AAS award in 1951.
‘Yellow Torch’ – has yellow-orange flowers.