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Gardening

Sennas, cassias burst with sunny blossoms

By JANE WEBER
Published December 11, 2006

The most stunning yellow-flowering shrub of the fall is probably Senna hicapsularis, still commonly called Christmas cassia by most local gardeners. A few years ago the large Cassia genus became better understood by botanists and was sorted into two groups: Senna and Cassia.

Cassia now contains more than 100 species of shrubs and small trees from tropical and subtropical regions around the world. Either evergreen or deciduous, cassias have pinnate leaves and clusters of simple, golden-yellow flowers with prominent long stamens.

Most cassias bloom for months and have large, bean-like seed pods. They bloom best in full sun and are not fussy about soil, provided it is well-drained and contains enough humus.

Golden shower, Cassia fistula, grows in warmer parts of South Florida. Its summer flowers hang in large clusters like bunches of grapes.

The pinnate leaves have three to eight opposite pairs of large leaflets, pointed and longer than the width, along the leaf stem (petiole).

Native to tropical Asia, this exotic tree can grow to 30 feet. Frost will kill it to the ground. Prune it in late fall to control the size. A hard freeze could kill the roots. Protect them with a pile of pine straw over the winter.

Golden shower is available only in summer. A 10-inch-wide pot wholesales for less than $10 and can be special-ordered at retail outlets. Overhead, shipping and handling will almost double the price.

The Senna genus has more than 260 species of fast-growing, mostly evergreen shrubs and small trees that grow in warmer, temperate to tropical zones around the world.

Most were formerly classified under Cassia. All have compound leaves with pairs of oval, opposite leaflets.

Few sennas tolerate living in artificial bark medium or heavily watered pots, and thus are available only from specialized and native plant growers.

Quite common in local gardens is exotic and frost-tender candlestick plant, Senna alata, with clusters of waxy erect flowers in summer. It has alternate compound leaves to 20 inches long with seven to nine oblong leaflets and no nectar glands on the petiole. It usually resprouts in spring with several stalks that can reach 20 feet.

The small shrub now blooming bright yellow all over Citrus County is usually Senna hicapsularis, misnamed Christmas cassia.

In my garden this senna, about 12 feet tall, has been in full bloom since late October. I have not pruned it in five years except when leaning stalks get accidentally snapped off by the tractor. It is past due for a haircut.

Once the shrub stops blooming, I must tackle the pruning job in the new year. This gorgeous plant is too overgrown to just prune back a third of the height. I will have to nip out half of the thick stalks and wait a year for new shoots to regenerate before removing the rest.

I should try to remember to keep it trimmed yearly in late winter to encourage denser branching and heavier blooming in the fall.

Some exotic sennas rapidly spread from seed eaten and dispersed by wildlife. Valamuerto, Senna pendula, is a Category 1 invasive plant pest that takes over natural areas, displacing native species that local wildlife depend on.

Coffee weed, Senna obtusifolia, and septicweed, S. occidentalis, native to Central and South America, are now naturalized weeds throughout the state.

One species of deciduous, herbaceous, perennial senna is native to Florida. In uplands, on roadsides and disturbed sites is the rare Chapman's wild sensitive plant, Senna mexicana var. chapmanii. All sennas are host plants for the caterpillars of cloudless sulphur, orange-barred sulphur and sleepy orange butterflies. No butterfly garden should be without a senna for butterfly nectar, caterpillar food and the delightful floral display in fall.

Editor's note: This weekly article is provided by Jane Weber, professional gardener, grower, consultant, designer and environmentalist. Visit her Certified Florida Yard and Backyard Wildlife Habitat, 5019 W Stargazer Lane, Dunnellon. Call (352) 465-0649.

[Last modified December 11, 2006, 06:18:32]