Euphorbia : Greenhouse Plants
C – cool, minimum of 7°C (45°F) / W – warm, minimum of 13°C (55°F)
The most well known of these must bepulcherrima more familiar as the sold in their thousands in Britain at Christmas time and loved for their red, white or pink bracts. If you look closely in the centre of the bracts you will see the more insignificant true flowers. These familiar plants descend from tall shrubby plants native to Mexico. On visits to the warmer parts of the world much taller plants can be seen than those grown in Britain. Most of our plants are smaller growing strains that have also been dwarfed by the use of hormones before we buy them. This is why if you successfully keep a plant going it will seem to grow on a much larger scale than before.
A group of these plants makes a superb seasonal display for a greenhouse or conservatory but they need a minimum winter temperature of 13°C (55°F) to do well. After flowering cut off the dead bracts and allow the plants to become almost dry. After a month of this treatment (usually by April) plants can be pruned hard and watered to make them grow again. Repotting takes place now, or at least a top dressing. Retain the five best stems that sprout from the base and water and feed well throughout summer. Then comes the tricky bit which is getting them to produce their coloured bracts again; they need short days to do this. If your greenhouse is not affected by any unnatural light (including faint light from a street lamp) they will turn red naturally. However, if any artificial light does reach them you will have to set up a blacking out regime to give them no less than 14 hours of uninterrupted darkness per day. This should begin towards the end of September and continue for eight weeks. Black polythene can be used effectively for this but it must be removed daily to allow light in for the rest of the time. Cuttings can be taken of the shoots made by the plants after pruning. When you remove these you will see that they bleed white sap. Dipping them in water will stop this. I avoid hormone rooting treatments as sometimes these seem to burn the end of the cutting. I also root them singly in small pots as they dislike root disturbance at potting up time. It is important not to Over-water these plants at any stage.
E. fulgens is an attractive shrubby little species with small scarlet-orange bracts. They are grown in a similar way to the Poinsettia but need warmer treatment. They are occasionally sold as cut flowers. If you buy the stems of bracts you will probably be able to find good cutting material on them. E. millii (E. splendens) is the Crown of Thorns and is a succulent species with spiky stems and red bracts. There are also varieties which are yellow or pink. This has its origins in Madagascar and is just hardy enough to survive in the cool house along with other succulent Euphorbia.