Euphorbia pulcherrima (Poinsettia) Christmas Flower; 15°C/60°F; Mexico

Whereas most of the winter-flowering plants require cool and airy conditions indoors to maintain them in good condition, the poinsettia is the exception to the rule and must have reasonable warmth if it is to prosper. Although excessive temperatures are not required, it is important that the minimum should not fall much below that recommended above for any length of time. The growing position must be the lightest possible, and full winter sun will not present any problems, although if the plant is kept after flowering it should be shaded from strong sunlight in summer.

The bright green leaves are surmounted by large brightly coloured flower bracts. Bright red or scarlet is the usual colour, but pink and white forms are also available.

However, in spite of its need for more preferential treatment, the modern poinsettia is a very much more durable plant than its predecessors of two decades ago. In those days the varieties that were grown needed constant attention and constant temperature if their leaves were not to shower off. The modern plants are not only very much more attractive as pot plants, they are also very much easier to care for both in the home and in the greenhouse. Need for careful watering is reasonably critical, and one must practise a programme that permits the mixture to dry out between each watering, so that the soil is kept just moist; over-watering and badly drained soil will cause the leaves to lose their colour and eventually fall off. How to get plants to flower again for a second time has become an almost standard question when poinsettias are under discussion – many indoor plant growers can get them to grow perfectly well for a second and third year in their homes, but no flowers will appear.

To encourage flowering the simple answer is that the plant from mid-September onwards should not be exposed to artificial light in the evening, as additional lighting simply results in the plant producing more and more leaves at the expense of flowers, or bracts. Even a street light outside the window of the room in which the plant is growing will prevent it from flowering. A weekly dilute feed during the summer months should also encourage new flower production.

Poinsettias are propagated from tip cuttings, that is to say the top section of a growing shoot is removed with three or four leaves attached, and the lower leaf is removed before inserting the cutting in a small pot filled with equal parts peat and sand. Cuttings do better if they are in a mist propagating unit so that the leaves are continually moistened with a fine spray of water. Even in these conditions cuttings will often go limp and seem quite dead only to rally in a few days and begin to root in about a fortnight. Once rooted they should be potted into gradually larger containers using a loam-based mixture – addition of a little extra-peat will do no harm.

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