From a botanical perspective, it is physically possible to grow oleander (Nerium oleander) indoors, but it is a significant challenge that goes against the plant's fundamental nature. Oleanders are large, sun-loving, evergreen shrubs native to the Mediterranean region. They are genetically programmed for abundant, direct sunlight, warm temperatures, and excellent air circulation. An indoor environment is a poor substitute for its preferred conditions, meaning the plant will require very specific and consistent care to merely survive, let alone thrive. It will never reach its full outdoor potential of 15-20 feet in height and profuse blooming indoors.
Light is the single most important factor and the biggest hurdle. Oleanders are obligate sun-worshippers. To have any chance of success indoors, they demand the brightest possible location. A south-facing window that receives at least 6-8 hours of direct, unfiltered sunlight daily is an absolute minimum. Even this will be less intense than outdoor sun. Without this, the plant will become leggy as it stretches for light, produce few to no flowers, and its overall health will decline, making it susceptible to pests and disease. Supplemental full-spectrum grow lights will almost certainly be necessary, especially during the winter months.
Oleander prefers the same temperatures most humans find comfortable, between 65°F and 80°F (18°C - 27°C). It is crucial to protect the plant from both cold drafts from windows and hot, dry air from heating vents. While tolerant of dry air, oleander appreciates moderate humidity. Low humidity, common in heated homes, can encourage spider mite infestations. Grouping plants together, using a pebble tray filled with water, or employing a humidifier can help mitigate this issue. Good air circulation around the plant is also vital for preventing fungal problems and strengthening stems.
The plant requires a well-draining, quality potting mix to prevent root rot. Watering should be done thoroughly when the top inch of soil feels dry, allowing excess water to drain away completely. Do not let the plant sit in water. During its active growing season (spring and summer), oleander is a heavy feeder. A balanced, water-soluble fertilizer applied every 4-6 weeks will support foliage growth and encourage blooming. Reduce watering and cease fertilization entirely during the winter when the plant's growth naturally slows.
A discussion of oleander from a plant's perspective must include its defining defensive characteristic: extreme toxicity. All parts of the plant—leaves, stems, flowers, roots, and sap—contain potent cardiac glycosides. Ingestion of even a small amount can be fatal to humans, dogs, cats, and other pets. The sap can also cause severe skin irritation. This makes it a highly unsuitable houseplant for any household with curious children or pets that may chew on plants. The risk of a leaf dropping and being ingested is a constant and serious concern in an enclosed indoor space.
