Photo: Rachel Bernier
Question: I bought this plant about 2 years ago (it was much smaller then!), but it just keeps growing upward. How do I get it to branch out instead of producing a single central trunk?
Answer: Your plant is a crown of thorns (Euphorbia milii), also called Christ thorn. There are many cultivars with flowers in all kinds of colors and also varieties that branch a lot while others, like yours, rarely seem to branch at all. In my experience, thin-stemmed, small-leafed varieties tend to branch more readily than large-leaved, thick-stemmed varieties like yours.
To force your plant to produce branches, cut off the top. That eliminates “apical dominance” (when the main central stem is dominant over side stems) and forces the redistribution of growth hormones that will hopefully stimulate a few dormant buds further down on the stem to start to grow.
You can simply “pinch” your plant (using pruning shears: this plant is too thorny to pinch with only your thumb and forefinger!), that is, simply prune off the growing point, or you could cut the plant back severely, to maybe 4 inches (10 cm) from its base. That will force your crown of thorns to produce at least one branch and probably several.
Wear gloves when pruning a crown of thorns: not only is the plant very spiny, but its sap irritates the skin and is even poisonous if swallowed. And after pruning, spray the wound with cold water to cause its white sap to coagulate and stop flowing.
If ever your plant produces only one branch (and yes, that can happen), let the new stem grow for 6 months or so, then cut off the tip again. You sometimes need to prune more than once to force certain recalcitrant plants to grow multiple branches.
The other possibility would be to root the top of the plant when you cut it off (again, spray the wound with water to stop its sap from “bleeding”) and plant the rooted cutting in the same pot as the mother plant. If you do this 2 or 3 times, that will give you a dense cluster of branches that will look good even if your plant really isn’t doing much branching.
Try It On Other Plants
And removing the top of most other plants with an upright growth habit will have the same effect. Cut back the top growth of any plant capable of forming branches (palms don’t for example) and the plant will soon produce new shoots lower down.