Euphorbia lactea cv. 'White Ghost'
Euphorbia lactea is in fact a true tropical plant only hardy to 40°F and must grow it either in pot or in the ground in very protected location. This being said, it is one of the few columnar Euphorbias that do exceptionally well in very wet, humid climates. It needs bright light to partial shade for best appearance (the plant that shown here, to the right is the 'White Ghost' cultivar a highly variegated form which I grow in bright shade for even a small amount of sun burns it). It responds well to warmth, with its active growth period in the late spring and summer months and during this time it needs to be watered thoroughly when soil is dry to the touch (more than once a week during the height of summer). The most common failure in growing this plant is over watering, and during the winter months, waterings should be restricted to once over the winter. Another important key to success is drainage, using porous soil is imperative. This is a slow growing plant, though the cristate forms seem particularly slow growing. Cristate forms are usually grown as grafted plants and that may have something to do with their slow growth rate.
Euphorbia lactea forma cristata variegata
Many succulents exhibit the occasional 'monstrose' plant, where the variation from normal growth is due to genetic mutation. However, in the Euphorbia family, the crested growth can occur on normal plants. Sometimes it's due to variances in light intensity, or damage, but generally the causes are unknown. A crested plant may have some areas growing normally, and a cresting plant that looks like a brain, may revert to normal growth for no apparent reason. You can see normal growth in the bottom left of the top photo, this will need to removed so the crested section can continue to grow.