What Is the Proper Way to Trim Crown of Thorn Bushes?
Crown of thorns (Euphorbia milii) is a flowering shrub that grows 5 feet tall at most, while low-growing varieties work well as a ground cover. It's named for its thorns, but its evergreen leaves and clusters of flowers give the plant its offbeat appearance. Hardy in U.S. Department of Agriculture plant hardiness zones 9b to 11, crown of thorns is a low-maintenance shrub that appreciates a sunny spot. If you want to trim this slow-growing bush, several factors will influence the way you prune.
Before you start trimming stems, you'll need to choose an appropriate tool for the job. Crown of thorn plants leak a toxic, milky sap that can ruin pruning shears. Rather than taking your most expensive pair of trimmers to these shrubs, it's smart to use inexpensive knives that are easy to clean. You should also wear gloves and keep the sap away from your eyes, while keeping children and pets away while trimming. After pruning, spray the pruning wounds with cold water to stop the sap's flow.
If you want to keep your crown of thorns low to the ground, cut back the branches while leaving the axillary buds and sprouts intact. ( In other words, you should remove the branches back to a lateral branch. This is preferable to cutting the shrub into the exact size you want, as that sometimes leaves branches bare and stubby for years. The key to reducing a crown of thorn's size is looking for the green buds and cutting above them, so the buds will blossom after pruning.
If your crown of thorns is too dense, you can remove weak or crowded branches to make the plant more attractive. Rather than cutting the stem halfway back so it's hidden, remove it back to its point of origin, leaving the branch collar -- the swollen area at the base of the limb -- intact. You should also completely remove dead branches, as naturally they will no longer produce new growths or flowers.
Other Reasons to Trim
If you see a diseased branch on your crown of thorns, remove it immediately and disinfect the pruning tools afterwards to prevent the spread of infection. If you notice the plant isn't blooming, it's smart to prune back a few of the branches to their connecting limbs to revive blooming. You can also trim the ends of the stems to spark new growth for next year's blooming to make the bush appear more robust and colorful.