The Handbook on Oleanders

Martha Hanna Hensley

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It’s funny how you could see something all of your life,

And then one day really see it.

Dr. Barry Comeaux

Description

Plant Types and Structure

The most natural form of an oleander is globular, or upright and rounded, whether it be a dwarf or tall-growing plant. The foliage is normally full and dense, skirting the ground. With many new oleander hybrids appearing each year, a criteria for grouping by size as well as color seemed useful to determine varieties for foreground, middle, background or specimen use. It would also assist gardeners in colder climates by giving them a more accurate guideline for choosing plants to be grown in containers. After viewing thousands of oleanders around the world, we evolved a classification system of five categories of size — only to find that Clarence Pleasants had already defined an almost identical system! We have combined the two systems for the following classification of mature plants:

Growth Habits and Life Span

Oleanders are moderate to fast-growing shrubs that are relatively long-lived. Plants tend to send up numerous stems from the base in the larger forms, but growth is much more controlled in dwarf and petite varieties. There are named cultivars to suit every landscape situation from slow-growing, dwarf, rounded, tightly compact forms to tall shrubs that can be trained in a multitude of shapes such as standards (also known as single trunk or patio trees), multi-trunk or multi-stem specimens, and a variety of other forms that are fully covered under Pruning in the chapter on "Culture."

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Stems and Branches

Stems are basically upright with few branches, initially a medium green changing to grayish tan on maturing and with a clear (not milky), sticky sap. Branches are flexible and bear mostly terminal inflorescences subtended by three equal branchlets (slightly triangular at the apex), giving the appearance of a candelabra shape.

Ted Turner, Sr., owner of Turner's Gardenland in Corpus Christi, makes an interesting observation regarding growth characteristics of oleanders in the Corpus Christi area and southern Texas, in contrast with southern California and other parts of the world. According to Ted warm summer nights tend to elongate the stems between leaf nodes and the leaves themselves are larger. In a comparison of like varieties, the overall tendency is for plants in Corpus Christi to be slightly larger and more upright growing. This is a concept often overlooked in general horticultural literature.

Leaves

Oleander leaves are simple, narrow, lanceolate, thick and leathery, usually smooth and glabrous above, rarely puberulous beneath, and cuneate at the base with short petioles and a prominent mid-rib with faint lateral veins. Margins are entire and slightly revolute. Leaf color ranges from rich, deep green to gray-green above and lighter beneath. Leaves vary in length from 2 to 3 inches to more than 12 inches. Although the leaves are somewhat stiff and leathery, their shape and arrangement on the stems gives plants a fine to medium-textured appearance.  

Turner's Sissy King'

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Photo courtesy Monrovia Nursery Company

Tangier™

Inflorescence

Inflorescences are mostly terminal cymes, variable in size, bearing loose or dense clusters of flowers with sepal-like bracts beneath. Blooming occurs on the new growth with one cyme often producing as many as fifty to seventy-five flowers.

Flower Shapes, Sizes and Colors

Oleanders offer flowers in a wide range of colors and hues, in fact, almost every color of the rainbow is represented with the exception of the blue-violet spectrum. We have had reports of lavender flowers in Europe but will have to visit the oleander collections there and see for ourselves! There are great variations in the many shades of red and pink, especially when the corona is of a different color.

The satiny blooms are generally large and showy and may be fragrant, often highly so, or totally without scent. When flowers are pale to white, sepals are light green. In deeper colored flowers, sepals are usually dark red to burgundy. The corolla consists of five overlapping lobes that are twisted to the right in the bud stage. The stamens are attached at the apex of the corolla tube but are not exserted. The anthers are adhered to the stigma.

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Flower Shapes

There are three basic flower shapes with variations within each shape.

 1. Single — Five fused petals (corolla lobes) with a central corona, a corolla tube, and a calyx with five sepals. The petals may be pinwheel, windmill, star-shaped, or cup-shaped, with the arrangement of the corolla lobes varying from narrow and widely separated to broad and overlapping.

2. Superimposed corollas — The technical term for semi-double or hose-in- hose flowers. In this shape one corolla is superimposed inside the other with the corolla lobes of the two whorls alternating.

3. Double flowers — This is a complicated and irregular form and we have followed F.J.J. Pagen's definition:

The term "double" in describing a flower form is ambiguous, but in this classification it is defined by the following characters (not all characters may be present in the same flower):

-More than ten petals or petaloid parts.

-Irregularity.

-Some petals free, some fused.

-Petals with claws.

- Petaloid anthers.

- Broad, swollen buds.

The double oleander flower has an irregular structure. Although the flower basically is composed of two, three or even four whorls of petals in addition to the calyx, the system is usually distorted and often hard to unravel.

We have found considerable variation in the double flowers of many plants;

blooms on the same plant are often single, others hose-in-hose, and yet others double but with irregular differences even among the double forms.

Flower Sizes

Corollas are variable with average sizes ranging from 1 inch to 3 inches or more.

Flower Colors

Colors range from white to pale pink, many shades of medium to deep pink, bright red or cerise to deep red, pale yellow, medium yellow and many salmon shades, often with orange coronas. A strongly colored corona tends to significantly influence the apparent color of a single flower, especially if the corolla lobes are some- what cupped. The coronas often have an apical fringe and frequently exhibit vertical

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lines of a different shade. Coronas that are strikingly colored or striped impart different hues not only to the individual flower but to the entire inflorescence.

Fragrances

As we mentioned in the "Introduction," virtually all the oleanders we grew in India were highly fragrant, often delightfully so. There are a number of fragrant varieties grown in the United States but they are few relative to the number of cultivars. Oleander fragrances are nearly as difficult to identify as those of plumerias. Many of the varieties in India, and some in the United States, have a jasmine-like fragrance, others a sweet-spicy or musky scent. Fragrance is very subjective but among the people we interviewed the scent most often described for oleanders in the United States is that of vanilla with certain cultivars imparting a magnolia or bitter almond aroma. Ted Turner, Sr. stated that he has found all of them to be most fragrant in the morning, becoming less so as the day proceeds.

Turner's Elaine Turner™

Follicles and Seeds

Fruits are more readily produced on the fragrant varieties and free-blooming cultivars than on other varieties. The seed pods (technically bicarpellate follicles) look like bean or pea pods in the shape of two narrow downward curving horns and are subtended by the persisting calyx. (See photo pg. 80) They are variable in length from just over 2 inches to approximately 7 inches and are usually about ½ inch across.

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The follicles vary from dull or bright green in the immature stage to medium brown or reddish brown at maturity. One often finds them in the process of maturing with the tip turning brown and the end still green where attached. When ripe and beginning to dry, the follicles split longitudinally to reveal numerous light to dark tan seeds (usually at least 50, often up to 200) covered with very fine hairs and a coma (tuft of hairs) at the apex allowing for wind dispersal.

Mrs. Lucille Hutchings

...How love burns through the putting in the seed

On through the watching for that early birth

When, just as the soil tarnishes with weed,

The sturdy seedling with arched body  comes

Shouldering its way and shedding the earth crumbs.

 Robert Frost

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