Nerium oleander or oleander is the sole species presently classified in the Nerium genus and belongs in the dogbane Apocynaceae family. There are currently over 400 cultivars and it has been so widely cultivated for thousands of years that it’s difficult to tell where it originated from except that it is generally associated with areas around the Mediterranean. It has been mentioned in Biblical texts dating back to 450 BC.
This evergreen plant grows to 7–20 feet tall, although it is commonly grown as a shrub. The leaves are pale green and glossy when young, before turning darker as they mature and are 2–8 inches long and 0.4–1.4 inches broad. It produces white, red, or pink aromatic flowers that grow in clusters throughout the year.
The flowers need insects for pollination, even though the flowers don’t have nectar. The insects are deceived by the attractive flowers and go away disappointed. The fruit, a long capsule of 2-9 inches, splits open when mature to release the downy seeds. It tolerates both drought and wet conditions, but not frost.
This is an energetic grower, particularly in warm subtropical areas, where it is widely cultivated in parks, along roads, and gardens since it is an attractive flowering plant. It is commonly grown as a large shrub form, but it is pruned to grow as windbreaks and hedges around houses and farms.
While this plant can tolerate poor soil, drought, and extreme heat, it will produce more flowers and vigorous growth when given the right care.
It has been depicted in paintings by famous artists including Vincent van Gogh and Gustav Klimt among others
This plant loves bright sunlight and might not grow or bloom properly if it doesn’t get a daily dose of 4 hours in direct sunlight.
While it is drought-tolerant, regular watering will help it grow and thrive to its full potential. Water it generously every three days throughout its growing season so that the soil is evenly moist. Reduce watering in winter when growth slows down. Also, the frequency of watering depends on the amount of sun it gets and the temperature, needing more water in the hot months of summer.
This is a hardy plant and can tolerate high humidity as well as average room humidity levels of 40%.
It needs warm temperatures between 70-85°F when it’s actively growing and around 55°F in winter. Hardier varieties can tolerate intermittent lows of 14 °F, although the leaves might get damaged.
If it’s growing indoors, heating and reduced airflow can make it susceptible to pests like oleander scale, aphids, whitefly, mealybugs, and spider mites.
It can grow in any kind of well-draining soil. Provided that the plant doesn’t get water-logged, it should be just fine, add sand and organic matter to the soil but don’t worry too much about the soil as long as the pot has enough drainage holes.
This plant doesn’t like being crowded, so transfer it to a pot 1-2 inches bigger.
Young plants must be repotted annually and older plants every 5 to 10 years or when the roots grow through the drainage holes of the container. The new planting vessel should be only a bit bigger than the old one.
If you reach the largest pot size, trim down the roots on the sides and underneath. When finished, return the plant to its home with fresh soil.
Propagation can be accomplished from cuttings and seeds, although cuttings are faster and much easier to root and grow.
Note: Make sure you use gloves and protective eye gear when doing this since this plant is toxic.
Collect the little brown seeds that are attached to fine downy material that can be separated by rubbing the seed on a screen or simply by removing them by hand. Seeds can be planted in small pots or seed trays filled with damp peat.
Press the seeds onto the top but don’t cover them with peat and transfer them to a warm area around 68°F with bright light or under grow lights. Mist the peat to prevent it from drying. Germination will start within 1-3 months. Once they sprout and get a few leaves, they can be relocated to your garden or a larger pot if you want them to grow indoors.
You can take cuttings from either the greenwood or woody branches. Most growers note that greenwood cuttings root faster. Take cuttings around 8 inches long, cutting the stem below a leaf. Clip of all the leaves, leaving only 2-4 leaves on the tip.
You can simply plant cuttings in rich, organic compost. New shoots will appear after about 4 weeks, suggesting that roots have formed. It can be transferred to a pot filled with the same soil as mature plants.
Feed the plant with a balanced fertilizer once in 2 weeks until summer, then feed it with a fertilizer high in potassium to give the plant a boost during its flowering season.
While it doesn’t need pruning for it to thrive and flower, it can become untidy as it ages, with older branches becoming gangly and new growth shooting up from the base because of this, gardeners advise that the mature shrubs be pruned in the fall to shape and encourage better foliar growth and flowers in spring. Many gardeners also choose to remove the seed pods that divert energy from the plant (unless you want to harvest the seeds).
The pests that commonly affect this plant are oleander scale, aphids, whitefly, mealybugs, and spider mites. They can be controlled using insecticidal soap and a pesticide like neem oil.
Another pest damaging to this plant is the oleander caterpillar. It can defoliate the plant and must be quickly eliminated once you spot the caterpillars – pick them off leaves and drop them into soap water. Remove infested leaves or branches if the infestation is serious and dispose of the material to prevent them from spreading.
Note: Always wear gloves and protective equipment like goggles when removing oleander caterpillars as contacting them will cause an itchy, painful skin rash and eye inflammation and sensitivity if you touch your eyes.
Under- or over-watering might cause the leaves to turn yellow. Over-watering usually causes more harm to the plant by also initiating root rot. The plant will revive with proper watering but if the problem continues, then the issue is probably because of leaf scorch.
Leaf scorch in this plant is from a bacterial infection that causes leaves to become yellow and dry, delaying flowers from blooming. Unfortunately, there isn’t a proper cure and many plants have been decimated from this disease. Trimming might help but might not save the plant since the infection has moved throughout the plant already.
If the plant will not flower, examine its location as this plant needs full sun to flower properly. Make sure the plant is getting sufficient light and water. You can also feed it with a fertilizer that is higher in potassium and phosphorus to boost flower development.