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Growing Poinsettias for Christmas (starting in the summer)

Poinsettias are well-known and cherished for their vibrant, colorful displays that brighten our homes during the Christmas season. Growing your own poinsettias for Christmas is achievable for gardeners who have access to a heated glasshouse or, ideally, an indoor grow room. There are three key factors to consider when cultivating poinsettias:

  • Daylength
  • Heating,
  • Whitefly management

Daylength

The formation of the striking red bracts, which are often mistaken for flower petals, depends on the daylength. These bracts, which attract pollinators to the small flowers, can range in color from intense red to pale pink or yellowy white. Orange varieties are also proving somewhat popular at Halloween!

Commercial poinsettia production typically begins in mid-July by potting up cuttings obtained from specialist nurseries or online sources. Alternatively, poinsettias from the previous Christmas can be rejuvenated by cutting them back, repotting them, and providing a good dose of nitrogen fertiliser. Once potted, the cuttings are exposed to normal conditions for a few weeks before the daylength is artificially shortened to induce red bract formation. This short day period is usually initiated from mid-September and should be maintained until November for an impressive display. In a grow room, setting automatic timers for light control is simple, whereas in a glasshouse, blackout shading must be manually adjusted or automated to ensure the plants don’t grow excessively tall and green, as they would in their native Mexican habitat.

Poinsettia in their native Mexican habitat growing tall and unbranched.

Heating

Heating is a crucial aspect of poinsettia cultivation due to their sensitivity to low temperatures. These plants cannot tolerate cold air, and exposure to chilly conditions will cause the leaves to drop. Therefore, even when purchasing poinsettias from a store, it is essential to quickly transport them to a warmer environment. In the UK, where winter temperatures can be challenging, a significant portion of the cultivation cost goes toward heating the glasshouses to maintain a minimum night temperature of 10°C. Moreover, temperature control must be precise, as poinsettias can suffer from heat stress if temperatures exceed 21°C. The narrow temperature range of 11 degrees further emphasizes the importance of considering a grow tent for poinsettia cultivation. In such a setup, using a humidifier may also be beneficial, as these plants thrive under slightly humid conditions.

Whitefly management

Whitefly poses a significant threat to poinsettias and is the most common pest affecting them. These pests often enter the grow room or greenhouse from outdoor crops as the latter begin to enter dormancy in autumn. Whiteflies are particularly attracted to poinsettias and thrive under warm conditions. To combat them, spraying with Insecticidal Soap or Yucca Extract is recommended. If diseases such as mildew appear, adding a small amount of Lime Sulphur can help control them.

In addition to these primary considerations, poinsettias are sensitive to flooding and should not be placed in saucers of stagnant water, which can lead to waterlogging of the growing medium. Excessive water results in wilted leaves and leaf drop due to the accumulation of the stress hormone ethylene. Ethylene is also released from decaying leaves, and so it is crucial to promptly remove any fallen leaves to minimise ethylene levels. Furthermore, poinsettias benefit from magnesium-rich fertilizers, such as Epsom salts, as their leaves contain high levels of magnesium.

In conclusion, growing poinsettias for Christmas can be accomplished with proper care and attention. Controlling daylength, providing adequate heating, managing whitefly infestations, and considering factors like water drainage and nutrient supplementation are essential for successful cultivation. By understanding and addressing these key aspects, gardeners can enjoy the beauty of poinsettias and their colorful displays during the festive season.

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