Specialist nurseries in the UK who cultivate poinsettias spend six months caring for them prior to these plants being sold in supermarkets and garden centres in the lead up to the festive season. On average more than 8 million are sold in the UK every year. However, these glorious plants are not easy to grow, and many do not survive once they are in a home environment.
Poinsettias grow outdoors in Mexico and Central America and parts of Southern Africa where these shrubs can reach heights of up to 4.5m. The ancient Aztec people of Mexico grew poinsettias, seeing them as a symbol of purity. They named them ‘cuetlaxochitl’ which translates to ‘mortal flower that perishes and withers like all that is pure’. They used the red bracts to make dyes for fabric, and the milky sap they exude (which is an irritant to skin and eyes), to treat a variety of ailments. In the 17th century, the poinsettia – which blooms in such brilliant colours during winter – was adopted into nativity processions, like the Fiesta of Santa Pesebre.
Poinsettias (Euphorbia pulcherrima) are part of the same genus as the Euphorbia we grow in our gardens – in fact, all contain a mildly toxic sap when their stalks are cut. You can buy multi-headed plants, growing up to 60cm tall or smaller, single headed plants which are around 10cm tall. It is their colourful leaf bracts, in shades of red, pink, burgundy, salmon and cream which make these plants so attractive.
When you select your poinsettia, look for a fully grown, healthy plant with leaves that are not drooping or dropping off. In their natural growing environment, poinsettias receive warm night and daytime temperatures, and in the UK, they require a minimum temperature of 13oC (55oF) to survive. Thus, when we take our poinsettia plant out of a relatively warm shop in late November or December (through the cold as we walk across the carpark or to the bus stop and on to our final destination) it receives its first shock treatment. Within a few days, this is likely to lead to yellowing dropped leaves and damaged bracts. Help keep your poinsettia warm on the way home by asking for wrapping over the top of the plant or place it in a bag to protect it from the cold outside. Get it into your house as soon as you can and, if possible, buy your plant on mild, rather than frosty days to minimise exposure to the cold.
Once you get your poinsettia home it is vital you find the right location for it, away from draughts but also radiators or other heat sources. It also needs between 6-8 hours of either indirect sunlight or artificial light from an LED or fluorescent grow light of at least 20 watts per square 30cm area. To trigger blooming and brighter coloured bracts, these plants also need 12 to 14 hours of absolute, uninterrupted darkness every night for 8-10 weeks. To achieve this, you may need to move it into another room at night or have a specialised dark out cover for your plant. And finally, do not place your poinsettia on a windowsill. Not only could there be a radiator underneath but also when curtains are pulled the area becomes too cold and draughty. Find a table for your plant, one which is out of any direct sunlight.
When it comes to watering your poinsettia, less is more as they hate being over-watered. Check the dryness of the compost by inserting a finger 2.5cm deep into the soil. If it feels dry, then it is time to give it a drink using room temperature water. Either water from the top, ensuring the water goes into the compost and avoids the foliage until it drains freely from the base, or place the pot into a shallow basin of water for up to 15 minutes until the soil has absorbed what it needs. The compost must be moist and not saturated. Let it drain thoroughly before returning it to its outer container. There is no need to feed your plant whilst it is in flower but to give the plant additional humidity, avoid spraying but instead stand its pot on a shallow tray filled with gravel and a small amount of water. As the water evaporates, it provides natural humidity without wetting the bracts and leaves.
Occasionally poinsettia can succumb to grey mould if overwatered and it can also be affected by scale insects and mealybugs.
If your plant survives beyond the festive season and is looking healthy by the end of winter, you should be able to keep it going for another year. Firstly, prune back hard in April (to about 10cm) and keep it at a room temperature of at least 13°C (55°F). Apply a fertiliser with high potassium fertiliser, such as a tomato feed, once a month. In early May, repot using three parts peat-free John Innes No 3 mixed with one part grit. Grow on in a light, cool place over summer, with an ideal temperature of 15-18°C (60-65°F).
