Growing hydrangeas inside is possible but requires a specialized and consistent approach that differs significantly from outdoor cultivation. The plant’s nature as a deciduous, woody shrub means that keeping it healthy and encouraging repeat blooming indoors demands careful attention to environmental controls. Success relies on providing the proper light, temperature, and humidity, which are often challenging to maintain in a typical home setting. The most significant departure from standard houseplant care is the need to deliberately guide the hydrangea through a cold, resting period to ensure future flower production.
Selecting Varieties and Setting Expectations
The selection of the right cultivar is the first step toward successful indoor cultivation. The best choice is often Hydrangea macrophylla, the Bigleaf or Mophead hydrangea, which is the species most commonly sold as a forced, potted plant by florists. These forced plants are already primed to bloom and are a much better starting point.
It is important to manage expectations, as an indoor hydrangea will never achieve the same sprawling size or prolific annual bloom count as a mature shrub planted in the ground. Look for dwarf varieties, which are naturally more compact and better suited to container life. Starting with a healthy, nursery-grown plant ensures you have a specimen already adapted to container life.
Optimizing the Indoor Environment
Hydrangeas require a bright environment to thrive, which translates to bright, indirect light when grown indoors. An ideal placement is near a south- or east-facing window, where the plant can receive several hours of strong light without the intensity of direct afternoon sun. If natural light is limited, a supplemental grow light can ensure the plant receives the necessary energy for healthy growth and bud development.
Maintaining a cool and consistent temperature is necessary for the plant’s well-being, especially during the blooming phase. Daytime temperatures should ideally remain between 65–75°F (18–24°C), with a preference for cooler nighttime temperatures between 50–60°F (10–15°C). The plant should be kept away from common household drafts, such as those from exterior doors or heat registers, which can cause stress.
Due to the dry air common in most homes, humidity needs to be artificially increased for the hydrangea. A humidity tray, created by placing the pot on a layer of pebbles in a saucer filled with water, helps boost the moisture level immediately around the foliage. Alternatively, a room humidifier can maintain a higher ambient humidity, which helps prevent the leaves from developing crispy, brown edges.
Watering, Feeding, and Potting
A consistent watering schedule is vital, as the name Hydrangea suggests the plant is “water-loving.” The soil must be kept evenly moist but should never become waterlogged, which quickly leads to root rot. A thorough watering is best, ensuring the water runs out of the drainage holes, and the top inch of soil should be allowed to dry slightly between applications.
During the active growing season, the plant benefits from regular feeding with a balanced, water-soluble fertilizer. A schedule of fertilizing every two to three weeks is appropriate, but this should be reduced or stopped completely in the fall and winter. The potting container must have excellent drainage, and a well-draining soil mix rich in organic matter is recommended. Repotting into a container only slightly larger than the current one, perhaps every two years, helps refresh the soil and accommodate root growth.
The Critical Dormancy Period
To ensure the hydrangea produces new flowers, it requires vernalization—a necessary chilling period that simulates winter. This process must begin in the late fall once the leaves have dropped or when the plant has finished its blooming cycle. The goal is to move the potted plant to a cold, dark location where the temperature can be reliably maintained between 35°F and 45°F (2°C to 7°C).
Suitable locations for this cold storage include an unheated garage, a cool basement, or a shed. During this time, the plant is resting, so the frequency of watering must be drastically reduced, only providing enough water to keep the soil from becoming completely dry. This chilling period needs to last for a minimum of six to eight weeks to properly set the flower buds for the next season.
After the required cold period is complete, the plant can be gradually brought out of dormancy to prepare for spring blooming. This process involves moving the plant to a slightly warmer room, around 50°F (10°C), where it receives bright, indirect light for a few weeks. Once new leaf growth is observed, the plant can be moved back to its normal, warmer growing location, and the regular watering and feeding routines should be resumed.