Crown of thorns, or Euphorbia milii as you may see it labeled at the nursery, is a member of the spurge family and a close relative of the poinsettia. This is a succulent and comes in climbing and shrub varieties, with flowers in pink, red, yellow and white. The crown of thorns needs heat and sunshine so is most suitable to being grown in USDA zones 9 to 11. Wear gloves when working with the crown of thorns plant as the sap is poisonous and may cause skin irritation.
Choose a planting location for the crown of thorns that gets all-day sun. In very hot areas provide afternoon shade.
Remove any weeds from the planting area. Dig up the soil to a depth of 6 inches and remove any rocks or other debris.
Add a 2-inch layer of compost and, with the gardening fork, mix it in with the soil.
Dig a hole the same depth and twice the width of the pot in which the crown of thorns is growing. Tip the plant out of the pot and gently loosen the roots with your fingers.
Place the roots into the hole and back fill with soil. Tamp around the base of the plant to ensure good contact with the soil
Water the crown of thorns and then water once a week, if the soil is dry, during the growing period. When the plant is dormant, cut back watering to once a month. It is very important to allow the soil to dry, to at least the top 2 inches, prior to watering.