The Handbook on Oleanders

L. Lovenberg

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Flowers are the moments representation

Of things that are in themselves eternal.

Sri Aurobindo

Oleanders and the Apocynaceae Family

Oleanders are members of one of the most colorful groups of plants in the horticultural kingdom, the Apocynaceae or Dogbane Family. The family was named by A.L.de Jussieu in 1789. Accounts as to the number of genera are varied with Hortus III of the L.H. Bailey Hortorium citing about 130 and the Royal Horticultural Society's Dictionary of Gardening listing 215. The more than 2000 species within the family are comprised of trees, shrubs, vines, herbs, succulents and groundcovers, mostly of tropical origin, with many being the source of drugs (glycosides) to treat heart disease and rubber which is commercially obtained from others. Some of the genera, popular for their ornamental value, have seen an explosion of interest from hybridizers and the gardening public in the past twenty years and have led to many exciting new varieties.

Since the late 1980's we have seen a burgeoning interest in flowering tropicals. Plants such as Mandevilla, unheard of by the greater gardening public a decade ago, are now regularly seen at nurseries everywhere and enjoyed in gardens throughout the country. New varieties of Allamanda, Bougainvillea, ginger and Plumeria appear every year.

The genus Nerium, or oleander, is certainly near the top of the list in popularity. Other members of the family well known to gardeners in the United States are: Adenium obesum, Desert Rose; Allamanda spp.; Carissa, Natal Plum; Catharanthus, commonly known as Vinca or Periwinkle; Mandevilla spp.; Pachypodium; Tabernaemontana, known in much of the United States as Carnation of India and elsewhere as Crepe Jasmine; Thevetia, Yellow Oleander; Trachelospermum, Star Jasmine or Confederate Jasmine, and its groundcover relative the Asiatic Jasmine; and Vinca major and Vinca minor, also known as Periwinkle, those ubiquitous and attractive groundcovers for shade and partial sun available in blue, white or lavender-purple flowers.

Listed below are brief descriptions of a few of the family members that are allied to the colorful oleanders. (See photos, pgs. 8 and 9)

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Adenium obesum — Desert Rose. The genus Adenium contains about four species native to tropical Africa. A. obesum, the Desert Rose, is a slow-growing plant that lends itself admirably to bonsai culture with its swollen caudex and large, red to pink flowers set against dark green leaves. This is a very drought resistant plant that stores water in its stem and is relatively free of pests and disease. In recent years many new cultivars with flowers in shades of cream, rose-purple and lavender have been introduced. We have seen a report in a recent issue of Nerium News from our longtime friend Mr. R. Haresh of Madurai, India, indicating that hybridizers there have crossed the Adenium with Nerium oleander. We can't wait to see the results as they are certain to be unique! F.J.J. Pagen, in Oleanders, Nerium I. and the oleander cultivars, states that Adenium is the most closely related genus to Nerium and that Adenium species may be grafted on Nerium oleander rootstock to produce profusely flowering plants.

Allamanda — A genus of approximately twelve species, all native to tropical America. The showy, often very large flowers range from cream to yellow to purple and are borne in profusion over a long blooming season. Many new cultivars have been introduced during the 80's and 90's. Some of the new hybrids are notable for a number of characteristics such as dwarf forms suitable for groundcovers and container culture, and new colors in shades varying from cream to rose-purple.

Carissa — A genus native to the Old World Tropics containing thirty-five species of small evergreen shrubs and trees, mostly with spines. The most popular members make handsome hedges or ground covers and produce an abundance of very fragrant, white to pink flowers. Some species produce edible fruits that may be made into an excellent jam. Pictured on Pg. 9 is one of the compact forms Carissa grandiflora 'Compacta', a low-growing ground cover or small hedge that flowers freely throughout spring and summer.

Catharanthus — About five species of erect annual or perennial herbs native to the Old World Tropics belong to this genus. The most popular form is Catharanthus roseus, known to most gardeners around the world as Vinca (Annual), Periwinkle, Madagascar Periwinkle or Old Maid. In the past ten years plant breeders have created some of the most beautiful hybrids imaginable with much larger flowers, greater disease resistance, more compact forms and a wealth of new colors.

Mandevilla — All Mandevillas are native to tropical America, especially Argentina, Bolivia and Brazil. This is a large genus comprising nearly one hundred species, usually vines and scandent shrubs. Extensive breeding work is in progress in the mid 1990's and some of the new hybrids are truly breathtaking. We have seen recent crosses of M. 'Alice du Font' with deep red flowers, pale pink and white flowers, and a pure white hybrid, all with blossoms as large or larger than the original cultivar!

Mandevilla x amabilis 'Alice du Pont' — A magnificent vine of moderate growth producing large, bright pink flowers (up to 4 inches across) set against medium green leaves. An excellent plant for containers as it flowers from spring to fall in most areas.

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Mandevilla boliviensis — White Dipladenia. A species that has become very popular in recent years and is propagated by major growers across the United States. This is a small vine that is easily grown in containers and one we've seen flower in 4 inch pots, in bloom from spring through fall.

Mandevilla sanderi 'Red Riding Hood' — An excellent variety for container culture, especially hanging baskets, as it tends to spill rather than climb. Flowers are smaller than the varieties mentioned above but are unique for their rich, deep pink color. Plants are especially attractive for the small, glossy, deep green leaves that have a bronzy tinge when young.

Mandevilla sanderi 'Rosea' — Brazilian Jasmine. A delightful small vine with glossy, dark green leaves that are bronze beneath and in the new growth. Flowers are trumpet-shaped in a delicate, clear rose- pink with a yellow throat. Plants bloom on and off throughout the growing season and sporadically all year in warm climates or greenhouses.

Plumeria — Frangipani, Temple Tree, Hawaiian Lei Flower. Since plumerias were the subject of our first book you can imagine that we are partial to them. Available in a rainbow of colors with large, often intensely fragrant flowers, new dwarf hybrids, and a flowering season that extends from spring until fall, plumerias are an excellent choice as companions for oleanders. Since they are not nearly as hardy, however, they must be given full winter protection except in tropical climates. The following three plumerias are representative of hundreds of cultivars and species grown around the world:

Plumeria 'Aztec Gold' — Large, buttercup yellow flowers with a faint pink band on the reverse and a heady, strong fragrance reminiscent of fresh peaches.

Plumeria 'Kimi Moragne' — Very large, sweetly fragrant, intense rose-pink flowers shading to lighter pink at the extreme edge of each petal and a golden-yellow center. Clusters are very dense with many blooms open at a time. One of many extraordinary hybrids created by the late Bill Moragne in Hawaii.

Plumeria 'Singapore' (P. obtusa) — This species bears pure white, perfectly shaped flowers with small yellow centers and the typical, exotic, Frangipani fragrance. Unlike varieties of P. rubra, plants are evergreen and have thick, leathery, glossy, dark green leaves.

Tabernaemontana divaricata — Crepe Jasmine, Carnation of India. A very handsome shrub of moderate growth with soft white flowers set against glossy, dark green leaves. Select cultivars are available with single, semi-double and fully double flowers. Recently a very compact dwarf form was introduced.

Thevetia peruviana (T. neriifolia) — Yellow Oleander, Be-Still Tree. A color- fall member of the Apocynaceae family often used as a hedge or screen in tropical climates. The term Yellow Oleander implies that it was formerly believed to be a

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Family Members

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   Family Members

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 variety of oleander. Forms with white, yellow and orange flowers exist as well as a rare, large-flowered species T. ycotii with buttery yellow blooms. All parts of this plant are extremely toxic and we have known the fruits to be chewed by people in southern India to commit suicide.

Trachelospermum jasminoides — Star Jasmine, Confederate Jasmine. A favorite ground cover plant in southern California, especially on slopes, and highly valued everywhere for its sweet fragrance that can perfume an entire garden. In cooler areas it is a superb container specimen, especially striking set against a trellis with its white flowers appearing like stars against the dark green foliage. Virtually evergreen in Zones 9 and 10, it will withstand below freezing temperatures for short periods. A yellow flowered form T. jasminoides 'Mandianum' is also available.

Urichites lutea — Yellow Mandevilla. A small flowering vine only recently introduced to American gardeners. The glowing golden-yellow, trumpet-shaped flowers are set against attractive, glossy, medium-green leaves.

Vinca — A genus consisting of approximately twelve species, all native to the Old World. The two most popular for ground covers and window boxes are listed below:

V. major — Greater Periwinkle, Blue-Buttons. An excellent ground cover for shady, moist areas, this hardy plant is grown throughout much of the United States. A few unusual varieties are available including a variegated form 'Variegata' (or 'Elegantissima'). Flower color varies from blue to deep purple.

V. minor — Common Periwinkle, Lesser Periwinkle, Myrtle, Running Myrtle. Generally hardy to Zone 3 and further north if heavily mulched or protected by snow. Growth habit is very prostrate with plant height from 3 to 6 inches. Can take full sun in more northerly zones but prefers some shade from Zone 8 south. One of the best ground covers for its compactness, ease of culture and lovely flowers that range from white to violet-pink, blue and purple, with the most frequently seen shade a lovely lilac-blue.

Quiz

If the question were asked, "What plant can you name that has all of the following attributes?"...

1. Drought tolerance

2. Insect resistance

3. Disease resistance

4. Wind tolerance

5. Salt tolerance

6. Smog tolerance

7. Fast growing

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8. Very easy to grow

9. Ideal container plant

10. Superb windbreak

11. Many dwarf forms

12. Highly fragrant forms

13. Able to withstand intense heat, even that reflected off concrete and asphalt

14. Able to withstand automobile pollution and frequently planted on freeways

15. Able to grow in widely divergent soil conditions from sand to clay and gravel

16. Grows equally well in the desert and at the seaside

17. Needs little fertilizer but responds well to fertilizing

18. Excellent choice for hedges and privacy screens

19. Tolerates light freezes and although sometimes killed to the ground in temperatures below 20° will regenerate in the spring

20. As a landscape subject makes an ideal background plant (large shrub forms), middle ground specimen (intermediate forms), and foreground subject (dwarf forms)

21. Evergreen in warm climates

22. Available in a wide range of colors

23. Flowers abundantly from spring into fall

24. Cultivars available with single or double flowers

25. Ideal foundation plant against a wall (See photo Pg.104), border plant (dwarf forms), or as a foil or complement in architectural settings

26. Produces large clusters of extraordinarily delicate and lovely blooms

... Your answer might well be, "None, such a plant doesn't exist. It's a figment of your imagination!" Fortunately for gardeners around the world such a plant does exist and it's the oleander, a plant that for many rivals in beauty the camellia of northern gardens. Few plants offer so much beauty with so little care.

Flowers ... have a mysterious and subtle

influence upon the feelings, not unlike some

strains of music. They relax the tenseness of

the mind. They dissolve its rigor.

Henry Ward Beecher,

 Eyes and Ears

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