Keeping poinsettias vibrant requires understanding their specific needs, especially when attempting to rebloom the plant. The most confusing aspect of year-round care involves the specialized dark treatment period necessary to produce the iconic colored leaves, or bracts. This process introduces a unique challenge for home growers, who must determine how to meet the plant’s moisture requirements without disrupting the delicate cycle of light and darkness. The approach to watering during this phase is different from the rest of the year, demanding careful attention to the plant’s reduced metabolism.
Watering During the Dark Treatment Phase
Yes, poinsettias must still be watered when they are placed in total darkness, but the frequency is significantly reduced compared to when the plant is actively growing. The darkness treatment, which begins around late September or early October, lowers the plant’s overall metabolic rate. This decrease means the plant uses water much more slowly, making overwatering a substantial risk during the eight to ten weeks of this process.
The correct procedure involves checking the soil moisture just before the plant is moved to its dark location for the night. You should only water the plant if the top one to two inches of the potting mix feel dry to the touch. If the soil is still slightly moist, skip the watering for that day and check again on the following day. When watering, it is important to soak the soil thoroughly until water drains from the bottom of the container.
Watering must be done while the plant is in the light, immediately before it goes back into darkness, or immediately after it emerges for its daily light exposure. Allowing the plant to drain completely for at least 30 minutes is necessary before placing it into the dark area. Sitting in standing water, even for a few hours, can lead to root rot.
Understanding Why Poinsettias Need Darkness
The need for a strict dark treatment is rooted in the poinsettia’s biology as a short-day plant, a phenomenon known as photoperiodism. This means the plant’s reproductive cycle, which includes the formation of the colorful bracts, is triggered by a long, uninterrupted period of darkness. Specifically, the plant requires 14 to 16 hours of continuous, total darkness every day for six to eight weeks.
This extended dark period signals to the plant that the days are becoming shorter. The darkness is a biological cue that switches the plant from vegetative growth to reproductive growth. Any interruption of the dark cycle, even brief exposure to a streetlight or a flashlight, can disrupt the chemical signal and delay or prevent the bracts from turning color.
The purpose of the bright bracts is to attract pollinators. This requirement for a precise dark duration is why the specialized watering schedule must be followed carefully to avoid disturbing the plant once it is secured in its dark environment.
Year-Round Watering Guidelines
When the poinsettia is not undergoing the dark treatment phase, its watering needs require consistently moist soil. During the holiday display period and throughout the active spring and summer growing seasons, the plant should be watered when the top surface of the soil feels dry to the touch. This often translates to watering every few days, depending on the temperature and humidity of the environment.
Proper drainage is necessary, as sitting in water will quickly lead to root rot. If your plant is wrapped in decorative foil, it is necessary to poke holes in the bottom or remove it entirely before watering to ensure all excess moisture can escape. Water should be applied at the base of the plant until it flows out of the drainage holes.
Discard any water that collects in the saucer beneath the pot after about ten minutes to prevent the roots from soaking. It is also beneficial to use slightly warmer water, as cold water can shock the roots. Finally, avoid wetting the leaves and bracts during watering to help prevent the development of fungal diseases like powdery mildew.