Sunflower Trees

I'm often asked where I got my Sunflower Trees and how one can grow some of their own. I've sent cuttings to people around the world, but with a warning, they are not for the lazy gardener. In the Florida summer they can grow out of control to 30+ feet (10 m). They have to be trimmed and pruned to keep them in place at least every other week in summer.

Here, I've looked up all the uses for Sunflower Trees that I could find and put them together with some of my favorite photos of the trees, which after a few years are almost constantly in bloom.

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Sunflower trees are known colloquially by dozens of different names; Mexican sunflower, tithonia, tree marigold, Japanese sunflower, Mexican tournesol, Bolivian sunflower, Nitobe chrysanthemum, shrub sunflower, wild sunflower [English]; tournesol mexicain [French]; fleur la fête des mères, petite fleur soleil [French créole]; árbol maravilla, falso girasol, guasmara, jalacate, árnica de la tierra, girasolillo, crisantemo de Nitobe, margarita gigante, tornasol mexicano, girasol mexicano, girasol japonés, margarita isleña, margaritona [Spanish]; margaridão-amarelo, girassol mexicano [Portuguese]; Mexikanische Sonnenblume [German]; harsaga, kembang mbulan [Indonesian]; dã quỳ [Vietnamese]; ニトベギク [Japanese]; காட்டுச் சூரியகாந்தி [Tamil]; บัวตอง [Thai], are just some of the local names for this tree.

Scientifically, they are Tithonia diversifolia (Hemsl.) A. Gray [Asteraceae] which is a lot easier to remember than all those other local names for the plant. They have one synonym in the literature, Mirasolia diversifolia Hemsl

In Florida they are considered an invasive weed. In other parts of the world they are prized for their nutritional value and their ability to improve poor soil. Once established they are virtually indestructible. The only thing I've found that will kill them is cold and then its only a brief death as they almost immediately sprout new growth as soon as cool weather passes.

The plant has a unique ability to convert Nitrogen from the atmosphere into protein and essential minerals in its foliage. It thrives in our 98% quartz, extremely poor soil, because it extracts its "fertilizer" from the atmosphere.

Sunflower Trees are a tropical herb or shrub cultivated in many countries of Africa, Asia, and South America for its multipurpose value. As fodder, it is rich in protein, valuable for ruminants and rabbits, but less for poultry and pigs, probably due to the presence of fibre and antinutritional factors.

Morphology

Tithonia diversifolia is a woody herb or succulent shrub, stoloniferous, annual or perennial, that can reach a height of 30 feet (10 m). It has a taproot with many fine secondary roots. The herbaceous mass can develop from subterranean stolons (a creeping horizontal plant stem or runner that takes root at points along its length to form new plants). The leaves are alternate or opposite, sub-ovate, densely pubescent, 5-17 cm long x 3.5-12 cm broad. Each mature stem may bear several large yellow flowers, up to 12 cm in diameter. The tree prefers really mature stems for blooming. Where frequently pruned it will delay blooming until stems mature.

Utilization

Sunflower trees are used for a variety of purposes: ornamental, fuel, compost, land demarcation, soil erosion control, soil remediation, building materials and shelter for poultry. Sunflower trees are commonly used as fodder for ruminants and rabbits, who can eat the leaves, soft branches and flowers. Its potential has been tested in pigs and poultry with mixed results.

Distribution

Sunflower Tree is native to Mexico and Central America but naturalized in Florida. It was introduced into tropical regions of Asia and Africa, into Australia and several Pacific islands, including Hawaii, French Polynesia and New Caledonia. It escaped from cultivation and is now growing wild in many tropical regions. In Kenya, Sunflower Trees are one of the most popular indigenous fodder tree species in the sub-humid highlands, where it is frequently coppiced (cut back to create thicker plants) for denser fodder.

Sunflower Trees are a fast-growing plant that tolerates heat and drought and can rapidly form large herbaceous shrubs. It is adaptable to most soils. It is found in disturbed areas, abandoned and waste lands, along roadsides and waterways and on cultivated farmlands. It can be found from sea level up to an altitude of 1500 m.

My biggest issue with my Sunflower Trees is that they must be cut back frequently in the Florida summer or they become far too tall and unruly. I try to cut them back every couple weeks in summer with the last cut coming around the first of September. The tree prefers to bloom from old growth so cutting any later than September will hinder bountiful flowering in winter.

Establishment and yields

Sunflower Trees can be easily propagated by direct seeding or by planting of 20-30 cm long cuttings from green stems, at a spacing of 0.5-0.75 m x 0.75 m. They are easy to grow and do not require fertilizer or special attention. The plants tolerate regular heavy pruning. Post-flowering cuttings result in higher yields than pre-flowering cuttings. In Côte d’Ivoire, annual biomass yields of 60 t/ha have been obtained at cutting intervals of 4 months.

I established my 1200-foot hedgerow of Sunflower Trees from one stalk indiscriminately broken off a mature tree 6 winters ago. During my first summer with these trees I trimmed them often. At one trimming I put about 50-1 gallon pots out and stuck the sunflower tree trimmings in potting soil. I produced 50 new plants and thus started my hedgerow.

Environmental impact

Weed control and invasiveness

Tithonia diversifolia is a pioneering species that grows quickly and produces significant amounts of seeds. It can grow from its subterranean stolons and forms dense stands that prevent the growth of young native plants. In Thailand, it was used successfully to control Echinochloa colona (sawa millet, wild grass) in rice fields, where it increased rice tillering, leaf area and rice biomass production. However, Tithonia diversifoliais considered to be invasive in some parts of Africa and Australia, and in many Pacific islands.

Crop and soil improver, soil erosion control and soil remediation

Sunflower Tree produces a nutrient-rich (N, K and P) biomass and its positive effect on subsequent rice and maize crops has been reported from Africa and Brazil. Its abundance and adaptability, coupled with its rapid growth rate and very high vegetative matter turnover, makes it a candidate species for soil rejuvenation and improvement, as a green manure or as a major component of compost manure. Different practices have been reported: Sunflower Tree can be left to decompose on the field, or it can be turned into green manure. In the latter case, leaves and soft twigs should be cut and chopped into small pieces before flowering and the resulting mixture evenly spread on the ground before being incorporated in the soil. In Kenya, Sunflower Tree's green manure is profitable for high-value crops such as Brassica sp., French beans, tomatoes and Napier grass (Pennisetum purpureum). In the Philippines, 1 to 2 tons of freshly chopped Sunflower Tree forage was shown to have a positive effect on a sweet potato crops. From the Philippines, it was also reported that Sunflower Tree could be a potential organic foliar fertilizer for rapeseed. Sunflower Tree has a positive effect on crop yields when used in intercropping.

Sunflower Tree was used to control soil erosion in the Usambara mountains of Tanzania, but it was not as effective as Napier grass or Guatemala grass (Tripsacum andersonii). In Brazil, Sunflower Tree has been used for soil remediation along roadsides where heavy metals, and particularly lead, accumulate.

In the Florida garden Sunflower Tree attracts all types of insects but none (so far) appear to kill the foliage.

Nutritional attributes

Tithonia diversifolia foliage is rich in protein and comparable to forage legumes in that respect. However, variability is high with protein content ranging from 12% to more than 30% DM, depending on the stage of maturity and on the proportion of stems in the fodder. Likewise, fiber content is highly variable: ADF content varies from 23% to more than 40%. One study found that nutritive value was highest in the vegetative stage and decreased sharply during flowering, but another study reported very low protein values even at the pre-flowering stage. Stems were found to contain less than 10% DM of protein. Tithoniafoliage is rich in minerals (10-16% DM), particularly calcium.

Potential constraints

Antinutritional factors

Sunflower Trees contain limited amounts of secondary metabolites (tannins, flavonoids, esteroids, alkaloids, saponins, terpenoids and anthocyanidins) that can act as antinutritional factors. Though these antinutritional factors are in much lower concentrations that in other tropical forages, such as Leucaena leucocephala, it can be useful to reduce their level through air-drying. Decreases in white blood cell content have been observed in pigs and poultry fed increasing amounts of dried Tithonia diversifolia forage. This could be explained by the presence of terpenoids (sesquiterpene lactones) in the leaves.

Ruminants (cattle, sheep)

Sunflower Tree foliage is a valuable fodder for ruminants, due to its high protein content and relatively high digestibility and degradability. However, the expression of this potential requires supplementation with fermentable carbohydrates to improve rumen microbial growth, and/or to increase the supply of bypass protein. Most studies of Sunflower Tree foliage have involved sheep and goats.

Hedgerow of Sunflower Tree in background along fence line.

Palatability

In Venezuela, a series of comparisons of the palatability for cattle, sheep and goats of 11 tropical fodders showed that Tithonia diversifolia had a moderate palatability, much lower than that of Chlorophora tinctoria (dyer's mulberry) and white mulberry (Morus alba) for all three livestock species. It was less palatable than Leucaena leucocephala but as palatable as Gliricidia sepium for cattle and sheep, though Leucaena and Gliricidia were more palatable to goats. These differences may be explained by the presence of secondary metabolites such as polyphenols, terpens and saponins.

Digestibility and degradability

The protein of Sunflower Tree foliage is both highly digestible and highly degradable. In vitro protein digestibility has been found to be 77-79%. In vivo protein digestibility ranges from 68 to 84%. In sacco protein degradability of Sunflower Tree foliage is high (more than 80%). As a consequence, N excretion was higher and N retention was lower in growing goats fed with Tithonia fed alone compared to Stylosanthes or jackfruit foliage fed alone, or with Tithonia supplemented with cassava roots and/or mulberry foliage.

Dairy cattle

Sunflower Tree could be a potentially valuable forage for dairy cows though only one trial had been reported at the time of this writing. In that Colombian study, Tithonia diversifolia foliage replaced up to 35% (5.6 kg/d/head of fresh foliage) of the concentrate supplementation for grazing dairy cattle with no effect on milk production and quality.

Other Uses

There are countless other uses for Tithonia diversifolia. One of the most interesting found in the literature is for rabbits suffering from scabies, a recurring skin problem of rabbits raised in tropical countries, a Tithonia leaf extract (300 g of leaves extracted in 100 ml of water) applied 4 times per day over a period of 5 days on the affected areas was as efficient as ivermectin to treat the condition. This would be useful to any Florida hiker as well.