To get poinsettias to bloom, you must carefully control their exposure to light and darkness, as their flowering is triggered by specific periods of uninterrupted darkness.
Understanding Poinsettia Blooming
Poinsettias ( Euphorbia pulcherrima ) are photoperiodic plants, meaning their blooming cycle is directly influenced by the length of daylight and darkness they receive. The vibrant "blooms" are actually colorful leaves called bracts, which develop their rich hues when the plant experiences a consistent period of short days and long, uninterrupted nights.
- Darkness is Key: Flower and color formation in poinsettias are primarily triggered by extended periods of darkness, ideally 12 to 14 hours each night. This artificial shortening of days signals to the plant that it's time to produce its characteristic colorful bracts.
- Bright Light is Essential: During the day, poinsettia plants require as much bright, indirect light as possible. This allows them to absorb enough energy through photosynthesis for robust growth and the production of their vibrant color. Insufficient light during the day can lead to weak growth and poor color development.
Step-by-Step Guide to Reblooming Your Poinsettia
To encourage your poinsettia to rebloom and display its beautiful colors, follow a strict light and dark regimen starting in early autumn (typically late September or early October).
1. Preparing Your Plant
Before you begin the reblooming process, ensure your poinsettia is healthy:
- Pruning: Around late summer, prune back any leggy growth to encourage a bushier plant.
- Fertilizing: Feed your plant with a balanced houseplant fertilizer once every two to four weeks until the reblooming process begins.
- Watering: Keep the soil consistently moist but never waterlogged.
2. Implementing the Light and Dark Cycle
This is the most critical phase for successful reblooming.
| Requirement | Details |
|---|---|
| Darkness | 12-14 hours of total, uninterrupted darkness every night. Even a small amount of light can disrupt the process. |
| Light | 10-12 hours of bright, indirect light every day. Place the plant in a sunny window or under grow lights. |
| Duration | Maintain this strict light-dark schedule for 8 to 10 weeks, or until the bracts begin to show color. |
| Timing | Begin the regimen in late September or early October to have colorful bracts by the holiday season. |
Practical Application:
- Achieving Total Darkness: You can place your poinsettia in a dark closet, under a large cardboard box, or in a room that receives no light whatsoever during its dark period. Ensure no light from streetlights, lamps, or even electronics can reach the plant.
- Consistent Schedule: Adherence to the schedule is paramount. Missing even one day or interrupting the dark period can delay or prevent blooming.
- Temperature: During this period, ideal daytime temperatures are between 65-70°F (18-21°C), and nighttime temperatures should be slightly cooler, around 60-65°F (15-18°C). Avoid cold drafts or sudden temperature fluctuations.
3. Post-Blooming Care
Once the bracts have fully colored, you can return your poinsettia to its regular display location. The plant no longer requires the strict dark treatment, but it will still thrive in bright, indirect light and consistent moisture. Avoid placing it near heat vents or cold drafts, which can cause the bracts to drop prematurely.
For more detailed care instructions, you can refer to resources from reputable horticultural institutions like the Purdue University Extension or the University of Illinois Extension.
