To understand oregano's needs, we must first consider its origins. Most common oregano (Origanum vulgare) is native to the Mediterranean region. This means it is a perennial herb adapted to hot, sunny summers and mild, wet winters. It is not inherently equipped to handle deep freezes or prolonged periods of freezing soil. When temperatures drop significantly and daylight hours diminish, the plant's natural response is to enter a state of dormancy. It will die back to the ground, with its energy conserved in its hardy root system to await spring's return. Bringing it indoors is an attempt to interrupt this dormancy cycle by providing a warmer, more stable environment.
For oregano to not only survive but potentially thrive indoors, three environmental factors are critical from the plant's perspective. First is light. As a sun-loving species, it requires a minimum of 6-8 hours of direct, bright light daily. A south-facing window is ideal. Without sufficient light, the plant will become etiolated—stretching weakly with sparse, pale leaves as it desperately seeks a light source. This weakens it significantly. Second is temperature. While the plant appreciates warmth, it prefers cooler indoor conditions compared to tropical houseplants. A room temperature between 60-70°F (15-21°C) is suitable. Avoid placing it directly next to a heat vent, as excessive dry heat will stress it. Finally, humidity is a major concern. Heated indoor air is extremely dry, which is the opposite of the plant's preferred slightly humid Mediterranean climate. This low humidity makes the plant more susceptible to spider mites, which thrive in dry conditions.
Even under the best indoor conditions, it is important to adjust your expectations. The plant will undergo physiological changes. Its growth will slow down considerably. This is a natural reaction to the lower light intensity of winter, even in a sunny window, compared to the powerful sun of its growing season. You should reduce watering accordingly, allowing the top inch or two of soil to dry out completely between waterings. The plant's metabolism is slower, and its roots are far more susceptible to rot in cool, soggy soil. Fertilization should be halted entirely during the winter months, as pushing for new, weak growth will only deplete the plant's energy reserves.
A crucial but often overlooked aspect is the process of acclimatization, both when bringing the plant indoors and when moving it back out in spring. Abruptly moving the plant from its outdoor environment to a different indoor one is a significant shock. To minimize this, gradually introduce the plant to its indoor spot over a week or so before the first hard frost. The same careful process must be reversed in spring. After the danger of frost has passed, the plant needs to be gradually "hardened off" by spending increasing amounts of time outdoors over 7-10 days. This allows it to re-adapt to direct sun, wind, and outdoor temperature fluctuations without suffering sunscald or shock.
