The Crown of Thorns plant (Euphorbia splendens) resembles a cactus, and like many cacti, every bit of the plant is covered with thorns except for the clusters of striking blooms. Crown of Thorns can be grown outdoors in warm, dry climates where the temperature never drops below 55 degrees F, but in most areas, Crown of Thorns is planted in containers. Grow it strictly as an indoor plant, or let it live outdoors and move it indoors during the winter months. If you're concerned about the thorns, plant Crown of Thorns in a hanging container and let it cascade safely over the sides.
Place Crown of Thorns in full, bright sunlight or supplement available sunlight with a grow light. If the Crown of Thorns plant has enough light, it will begin blooming during the summer and will continue for several months.
Allow the top inch of the soil to dry out before watering the Crown of Thorns plant, then water just until the soil is slightly damp. Don't be tempted to water before the soil dries out.
Feed Crown of Thorns twice each month using an all-purpose liquid houseplant fertilizer. Apply the fertilizer at half of the strength recommended on the package.
Keep Crown of Thorns in a warm environment at all times. The plant will drop its leaves if temperatures are allowed to fall below 55 degrees F.
Prune the Crown of Thorn plant as needed to encourage a bushy shape and to keep the plant from growing out of control. Using garden pruners, trim branches that are too long or those that detract from the desired shape of the plant. To stop the cut ends from "bleeding," spray them with cold water.