How to Make a Poinsettia Rebloom: 8-Week Darkness Schedule Starting October 1
Most poinsettias get thrown away after Christmas. Follow this step-by-step schedule to trigger the short-day treatment that turns green leaves red again — and have a fully rebloomed plant by the following Christmas.
The vast majority of poinsettias sold in the US are discarded in January. Most people assume the colourful plant they bought for Christmas is done for the year — a seasonal decoration like a wreath or a string of lights. That assumption costs you a free plant. A poinsettia kept alive through the year and given a specific darkness schedule from late September will develop fully coloured bracts again by December, reliably and repeatedly. This guide gives you the exact schedule, the science behind why it works, and the most common mistakes that prevent it from working.
Poinsettia is a tropical shrub native to Mexico, where it grows along roadsides and forest edges and blooms naturally in the short days of the subtropical winter. Understanding this origin is the key to understanding why the treatment works. For full growing guidance year-round, see our complete poinsettia care guide.
Why Poinsettias Need a Darkness Schedule to Rebloom
Poinsettias are obligate short-day plants, meaning colour development in the bracts (the modified leaves most people call petals) is triggered exclusively by the length of the dark period, not by temperature or season. This response is controlled by phytochrome, a photoreceptor protein in plant cells that shifts between two forms in response to red and far-red light wavelengths. When the dark period exceeds a critical threshold — approximately 12.5 hours per night for Euphorbia pulcherrima — the phytochrome ratio tips toward the form that initiates flowering and bract colouration [1, 2].
In practice, commercial growers target 14 hours of complete darkness per 24-hour cycle to ensure a reliable margin above the critical threshold. Home gardeners should use the same standard. Even a brief exposure to light — a lamp switching on for two minutes, a street light through a gap in the curtain — can reset the phytochrome cycle and delay or prevent reblooming [2]. This is the single most common reason home reblooming attempts fail.
The coloured bracts of E. pulcherrima are a member of the Euphorbiaceae family’s characteristic modified leaves used to attract pollinators to the inconspicuous true flowers (the small yellow-green cyathia in the centre). For more on the euphorbia family and its unusual physiology, see our euphorbia growing guide.
The Full Year-Round Schedule
The rebloom process spans approximately 12 months. The table below gives the complete calendar for a US indoor grower aiming for Christmas colour. All temperature ranges are in °F.
| Month | Stage | Action Required | Temperature |
|---|---|---|---|
| January–February | Post-holiday rest | Reduce watering; keep in bright indirect light; no fertiliser | 60–70°F |
| March | Prune and repot | Cut stems back to 4–6 inches; repot into fresh well-draining mix if rootbound | 65–70°F |
| April–May | Active growth | Move to brightest indoor light; begin fertilising every 2 weeks with balanced liquid feed | 65–75°F |
| June–August | Outdoor season (optional) | Move outdoors to a sheltered spot with morning sun; continue feeding; pinch shoots if needed for bushiness | 65–85°F |
| Early September | Bring indoors / prepare | Return indoors before temperatures drop below 60°F; stop pinching by September 15; keep in full sun during daylight hours | 60–70°F |
| Late September – late November | Short-day treatment (critical) | 14 hours complete darkness per night; 10 hours bright light per day; maintain for 8–10 weeks | 60–70°F |
| Early December | End treatment; display | Once bracts are fully coloured (around 8–10 weeks), stop the darkness treatment; place in normal bright indoor light; reduce feeding to once per month | 60–70°F |
How to Set Up the Short-Day Treatment
The darkness treatment is straightforward but unforgiving of shortcuts. Here is exactly how to do it.
Start Date and Duration
Begin the treatment in the third or fourth week of September. To have coloured bracts by Christmas Day, you need 8–10 weeks of treatment, which means starting by September 27 at the latest. Starting a week earlier — around September 20 — gives a buffer for any days where the schedule was interrupted.
Do not start the treatment earlier than mid-September. The plant needs the preceding active growth period to build the carbohydrate reserves that fuel bract colour development. Starting in August on an under-grown plant produces sparse, weakly coloured bracts [1].
The Darkness Period
Each evening, move the plant into a closet, an unused room, or place an opaque cover over it by 5:00 PM. Remove it or uncover it at 7:00 AM the following morning. This delivers exactly 14 hours of darkness. The darkness must be complete — a light-tight closet or a large cardboard box pushed firmly to the floor of a cabinet are the two most reliable methods for most homes.
If using a closet, test it first: stand inside with the door shut for 30 seconds. If you can read the time on a phone or watch, the closet leaks too much light. A gap under the door can be blocked with a rolled towel.
The Light Period
During the 10 hours of light (7:00 AM–5:00 PM), place the plant in the brightest south- or west-facing window available. Poinsettias need full sun during the day to continue photosynthesising and building colour. A plant left in moderate or low light during the treatment period produces pale, undersaturated bracts even if the darkness schedule is perfect [2].
Temperature During Treatment
Maintain nighttime temperatures between 60°F and 70°F (15–21°C) during the treatment period. Temperatures below 55°F (13°C) slow or halt colour development even when the darkness schedule is correct. Temperatures above 75°F at night can also reduce colour intensity. If your chosen dark location (basement, garage) drops below 60°F on cold September nights, move the plant to a warmer room each morning rather than leaving it in the cold closet overnight.
Month-by-Month Care: January Through September
January–February: Post-Holiday Rest
After Christmas, the plant enters a natural rest period. Reduce watering to once every 7–10 days, allowing the top inch of soil to dry out between waterings. Stop all fertilising. Move the plant to a bright windowsill away from heating vents and cold draughts. Temperatures between 60–70°F are ideal. The bracts will gradually fade and drop — this is normal, not a failure.
March: Prune and Repot
In March, once the last of the bracts have fallen, cut the stems back hard to 4–6 inches above the soil line. This hard pruning looks brutal but is essential — it forces the plant to produce multiple new shoots rather than a single leggy stem, resulting in a bushier, better-branched plant that produces more bract clusters in December [1].
If the roots are circling the bottom of the pot or emerging from drainage holes, repot into a container one size larger using a well-draining potting mix. A cactus and succulent mix blended 50:50 with standard potting compost works well, or any mix that drains freely within 30 minutes of watering. Poinsettias are susceptible to root rot in waterlogged soil. This is the same drainage requirement shared by many Euphorbiaceae relatives — our companion planting guide covers how grouping plants with shared soil requirements can simplify garden management.
April–May: New Growth
New shoots emerge from the pruned stems within 2–4 weeks of cutting back. Once the new growth is 2–3 inches long, begin fertilising every two weeks with a balanced liquid fertiliser (10-10-10 or equivalent). Move the plant to your brightest south-facing window. Growth is fast during this period — expect 6–10 inches of new stem length through April and May combined.
In late May, once nighttime temperatures are consistently above 55°F in your area, you have the option to move the plant outdoors.
June–August: Outdoor Growth (Recommended)
Moving the poinsettia outdoors for the summer months produces significantly better results than keeping it inside. Outdoor light levels — even in partial shade — are typically 10–20 times higher than indoor levels, and that high light drives the vigorous stem and leaf growth that fuels December bract development.
Choose a spot with morning sun and afternoon shade. Direct midday sun in Zone 7 and south can bleach the foliage. Shelter from strong winds is important because poinsettia stems are brittle. Continue feeding every two weeks.
Pinching: For a bushier plant, pinch out the growing tip of each stem when shoots reach 6–8 inches, leaving 4–6 leaves per stem. This encourages branching. Stop all pinching by September 1 at the absolute latest — pinching after this date removes the stem tips that will carry the Christmas bracts [1].
Early September: Return Indoors
Bring the plant back inside before nighttime temperatures drop to 60°F in your area — typically late August in USDA Zone 6, mid-September in Zones 8–9. Check carefully for pests before bringing it in: inspect the undersides of all leaves for whitefly, spider mite, and scale insects. Treat any infestations with insecticidal soap before the plant comes indoors.
Stop pinching by September 15 at the very latest. The plant needs the next two weeks of uninterrupted growth before the darkness treatment begins.
Troubleshooting: Why Your Poinsettia Is Not Turning Red
| Symptom | Likely Cause | Fix |
|---|---|---|
| Green bracts after 8 weeks of treatment | Light leak interrupting the dark period | Test the dark location by standing in it 30 seconds; seal door gaps with a rolled towel |
| Pale, washy bract colour | Insufficient daytime light during treatment | Move to the brightest south-facing window; supplement with a grow light (14 hours on) |
| Bracts beginning to colour, then going green again | Treatment stopped too early, or a single light interruption late in the cycle | Restart the treatment period from scratch if the interruption occurred in the first 6 weeks |
| Leaf drop during treatment | Temperature below 55°F in dark location, or draughts | Move to a consistently warm, draught-free dark space; check no cold air enters closet via HVAC vents |
| Few bract clusters despite good colour | Insufficient pruning/pinching earlier in the year; single-stemmed plant | Prune harder in March and pinch earlier next cycle to force more branching |
| Plant died or collapsed | Overwatering during rest phase (January–February) | Check pot drainage; allow soil to dry between waterings throughout the year |
Watering and Feeding During the Treatment Period
Continue normal watering during the 8–10 week treatment period — poinsettias are not drought-tolerant and will drop leaves if allowed to dry out completely. Water when the top inch of soil is dry, then water thoroughly until it drains from the bottom. Empty the saucer after 30 minutes.
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→ View My Garden CalendarReduce feeding to once every four weeks during the treatment period, switching from the balanced 10-10-10 used during active growth to a lower-nitrogen formula such as a 5-10-10 or tomato-type feed. High nitrogen during the colouring phase can push green leaf growth at the expense of bract development [2].
What to Expect: The Colouring Timeline
Colour changes do not happen overnight. Here is the typical progression:
- Weeks 1–3: No visible change. The phytochrome response is building internally. Maintain the schedule exactly — this is when most gardeners lose patience and abandon the treatment too early.
- Weeks 4–5: Tips of the uppermost leaves (the future bracts) begin to show the first flush of pink or red pigmentation. This is anthocyanin synthesis starting in response to the accumulated short-day signal.
- Weeks 6–7: Colour intensifies noticeably across the upper bract leaves. The lower green leaves remain unchanged.
- Weeks 8–10: Full colour development. The bracts reach their maximum colour saturation. The small yellow-green cyathia flowers in the centre open, confirming the plant has fully flowered.
Once full colour is achieved, move the plant back to its normal display position. It will hold colour for 4–8 weeks in a cool room (60–65°F) with bright indirect light and no draughts. Warmer rooms and low light shorten the display period.
Frequently Asked Questions
How long does the darkness treatment take?
8–10 weeks of 14 hours of complete darkness per night is the standard treatment for full colour development. Starting around September 20–27 reliably produces coloured bracts by Christmas. Some early-responding plants show colour after 7 weeks; most plants need the full 10 weeks for maximum colour saturation [1].
What happens if I miss a day of the darkness treatment?
A single interruption in the first four weeks of treatment is not catastrophic but does set back the timeline by a few days. An interruption in weeks 7–10 (when colour is already developing) is less damaging. If you miss multiple consecutive nights, restart the 8-week count from the last uninterrupted night. The plant has not been permanently harmed — the phytochrome clock simply resets.
Can I rebloom a poinsettia in an apartment with limited light?
Yes, with a modification. Replace the natural daylight period with 10 hours of a full-spectrum grow light (5000–6500K) placed 12–18 inches above the plant. The darkness period requirements are unchanged — 14 hours of complete darkness nightly. Apartment growers often find it easier to place the plant in a closet at 5 PM, set a phone alarm, and retrieve it at 7 AM — a routine that becomes automatic within a week.
Does the poinsettia need to lose its old leaves before reblooming?
No — and in a well-kept plant, you want to retain as many healthy green leaves as possible through the year to maintain photosynthetic capacity. The plant will naturally shed its Christmas bracts in January–February. New foliage grows during the spring and summer active period. The fresh green leaves present in September are the ones that will become the coloured bracts in December.
Will a rebloomed poinsettia have the same colour as when I bought it?
Yes. Bract colour is genetically fixed by the cultivar. A red-bracted poinsettia will produce red bracts each time it reblooms. However, home-grown plants often produce slightly smaller or less uniform bracts than the original commercial version — commercial growers use precise temperature manipulation and controlled lighting that is difficult to replicate exactly at home. The rebloomed plant will still be a genuinely attractive display plant.
Is poinsettia sap dangerous?
The milky white latex sap of poinsettia (like all euphorbias) is a skin and eye irritant. It is not lethally toxic as popular belief holds, but contact can cause dermatitis in sensitive individuals, and ingestion causes gastrointestinal discomfort. Wear gloves when pruning and wash hands immediately after handling cut stems. Keep the plant out of reach of young children and pets. The ASPCA classifies poinsettia as mildly toxic to cats and dogs [3].
