Oleander (Nerium oleander) is a versatile and resilient evergreen shrub, prized by gardeners for its prolific, showy blooms and tolerance of challenging conditions like heat, drought, and poor soil. From a botanical perspective, selecting a cultivar involves understanding variations in growth habit, flower morphology, and foliage, all of which influence its role in the landscape.
The primary consideration is the plant's mature size and form. Standard oleanders are vigorous growers, typically reaching 8 to 20 feet in height and width. They possess a strong, upright growth pattern with multiple woody stems, making them ideal for use as a tall screening hedge, a windbreak, or a dramatic specimen plant. In contrast, dwarf cultivars, such as 'Petite Pink' or 'Petite Salmon', are a result of selective breeding for compactness. These plants exhibit a much slower growth rate and a denser, more mounded habit, rarely exceeding 3 to 5 feet. This makes them perfectly suited for smaller gardens, container planting on patios, or low borders where the larger species would be overwhelming.
The flower structure of oleander is a key identifying feature. The classic flower form is single, consisting of five petals radiating from a central corolla tube. However, many cultivars display double or even triple flowers, where the stamens have been transformed into extra petaloids, creating a fuller, rose-like bloom. The color palette is extensive, ranging through various shades of white, pink, red, coral, and yellow. The cultivar 'Sister Agnes' produces large, single, pure white flowers, while 'Mrs. Roeding' offers fully double, soft peach-pink blossoms. The intensity of fragrance also varies significantly between cultivars, an important sensory consideration for planting near seating areas.
While renowned for flowers, oleander foliage offers decorative variety. The typical leaf is lanceolate, leathery, and deep green, arranged in whorls of three or four around the stem. This dense foliage provides excellent evergreen structure. Certain cultivars have been selected for distinctive leaf variegation, which provides visual interest even when the plant is not in bloom. For example, Nerium oleander 'Variegatum' features leaves edged in a creamy white, and 'Hardy Red' often has distinctly twisted leaves. These variegated forms can brighten a shrub border and are often slightly less vigorous than their all-green counterparts.
It is crucial to address that all parts of the oleander plant are highly toxic if ingested, containing cardiac glycosides such as oleandrin. This is a defensive trait the plant has evolved. This characteristic is consistent across all cultivars, without exception. Therefore, the selection process must include consideration of the garden's users. It is not advisable for gardens frequented by very young children or pets that may chew on vegetation. Always handle the plant with gloves when pruning to avoid skin irritation from the sap.
