Poinsettia is the popular name for Euphorbia pulcherrima, an ideal plant for the warm greenhouse. Itsare quite insignificant but they are surrounded by large leaf-like bracts (scarlet in this species) which are extremely showy. At one time these bracts were only seen around Christmas time – when they are especially welcome – but since the introduction of special light treatment we can have them in flower the year through. There are also pink and white varieties available now, and a dwarf form has been introduced from America.
I prefer to treat the poinsettia as a winter-flowering plant, producing its bright bracts between November and February. In this case the plants are cut back by half their height as soon as the bracts fade, and theis then left completely dry for this is the resting period. Watering should start again in early June and this will encourage the plants to produce new shoots.
The sideshoots that are produced when growth restarts are ideal to use as cuttings. The shoots are removed when they are 3 to 4 in. long and each is prepared in the usual way. The cut ends being dipped in sand to prevent ‘bleeding’. (Poinsettias have a very milky sap which flows profusely when the tissue is cut.) The cuttings should be inserted round the edge of pots filled with a mixture of loam, sand and peat, and placed in a propagating frame with a temperature of 21°C. (70°F.) or more.
An alternative is to cut up the stems made in the previous year into pieces about 2 in. long. If these are treated like ordinary cuttings they will soon form roots.
Plants raised from cut tings taken in May and June will grow to a height of about 6 ft. before the end of the year, but if smaller plants, about 12 in. tall, are required, cuttings can be taken in July. Three small plants can be put in a 5- or 6-in. pot.
When well rooted the cuttings are potted individually, first into 3i-in. pots using John Innes No. 1 Potting Compost and later into 5-in. pots using John Innes No. 2 Potting Compost. I prefer not to use pots above 5-in. size.
At first the plants should be grown in a warm rather humid greenhouse, with shade from the sun during the hot part of the day. As they become well established they can be accustomed to a lower temperature.
During August and early September the plants can be stood in a frame but they must be brought back into the greenhouse before there is any danger of frost, this being heated to 16 to 18°C. (60 to 65°F.) – more if early bracts are required. For the finest development of the bracts the plants should be restricted to one stem each and fed from late September until the bracts form with a soluble or liquid fertiliser.
Pay particular attention to watering as dryness will cause the leaves to turn yellow and drop. Fluctuations in temperature will also cause leaf fall.
After ‘flowering’ the plants are cut back and rested under the staging until growth starts again.