Why are my poinsettia leaves turning yellow? And how to keep yours alive indoors

Have your poinsettia leaves already started turning yellow? Perhaps its leaves are dropping, too? Keeping this Christmas staple alive and healthy indoors isn't always plain sailing.

Often part of a festive tablescape, mantelpiece, or windowsill display, a poinsettia's placement is key to it staying healthy, though it's not the only consideration when looking after a poinsettia to ensure it lasts until the 25th (and far beyond) without yellowing leaves. 

So if you've bought or been gifted a poinsettia for Christmas, and its leaves are already yellowing, it's probably caused by incorrect watering, the wrong light levels, a change in temperature that it doesn't like or fertilizing incorrectly.

Get it right and you can keep your poinsettia alive indoors right through to next Christmas. 

Why are my poinsettia leaves turning yellow?

'Poinsettias are fascinating plants. Given the opportunity and the right conditions, they can grow 13 feet tall,' says author Kate Russell from The Daily Garden. 

Light levels 

If your poinsettia leaves are turning yellow, it's likely that they are kept in a spot that's too dark for them. To keep poinsettias healthy in your winter home, Kate suggests giving them strong morning light and afternoon shade.

'Poinsettias only turn red when they are exposed to 12 hours of complete darkness for five days in a row. If your poinsettia starts turning green, give it some time in the closet.'

George Tandt, a house plant expert from Teak and Terracotta, emphasizes the need for bright sunlight but adds that you should never put your plant in direct sun.

Watering

Knowing when to water your plant is vital, too, to keeping your poinsettia alive indoors. 

'Allow the soil to dry out between waterings to prevent fungal diseases,' Kate says. 

'Overwatering is the biggest cause of them dying, so make sure you only water them when the soil is drying out, and after watering, don't leave any water in the saucer or container that the pot is in as that can lead to waterlogging and root rot,' says George. 

You should also ensure the plant is completely dried out before watering again. You can check the soil with your finger each week and water it if the top half of the soil is dry.

Temperature

Poinsettia are tropical plants, which means they enjoy warmth. But like other tropicals, they don't like heat that's too dry, so don't put them too near a fire or radiator; instead, keep them somewhere humid. Avoid, at all costs, putting them near a door that's used regularly or anywhere that's drafty; they dislike cold and sudden temperature changes, and this will ensure they die speedily.

Fertilizing

You don't need to fertilize a poinsettia that's indoors now; wait until spring and only apply to wet soil. 

How do I save my poinsettia for next year?

Despite its reputation as a Christmas plant, you can grow a strong, healthy poinsettia all year round. Kate recommends following this care schedule from the University of Vermont Extension:

• New Year’s Day – feed with all-purpose houseplant fertilizer
• Valentine’s Day – check for whiteflies; trim back to a height of 5 inches
• St. Patrick’s Day – remove dry and faded leaves; add fresh potting soil.
• Memorial Day – cut branches back 2 - 3 inches; repot into a larger container using fresh potting soil.
• Father’s Day – move the plant outside to a location with indirect light.
• Fourth of July – trim again; move into full sunlight; water and feed, as needed.
• Labor Day – rinse the plant off and move it indoors; reduce feeding as new growth appears.
• Autumnal Equinox – put plants in uninterrupted darkness for 13 hours and in bright light for 11 hours each day; nighttime temperatures of 60 degrees F are ideal.
• Thanksgiving – reduce water and feeding; place in a bright sunny window, rotating for full coverage.
• Christmas – enjoy and repeat.

How can I make my poinsettia leaves red again?

Healthy green poinsettias only turn their famous red when after enduring 12 hours of complete darkness for five days in a row. You should therefore put your poinsettia in the dark if you notice your leaves are green. 

If you're looking to re-flower your poinsettia, you should aim to keep the plant in the darkness between 5pm and 8 am daily from September. This should ensure it is red in time for the Christmas decor period.