Euphorbia milii, commonly known as Crown of Thorns, is an evergreen, succulent plant, native to Madagascar. Appreciated for its showy flowers and lush, thick, gray-green leaves, the Crown of Thorns is a good choice for outdoor beds or mixed borders in U.S. Department of Agriculture hardiness zones 10 through 15. In cooler regions subject to frost, it does well as a houseplant in a sunny window and can successfully overwinter indoors.
Crown of Thorns cactus produces succulent, woody stems that can reach up to 3 feet (90 cm). These thick stems store water, making the plant exceptionally drought-resistant. The plant derives its name from large, sharp spines about 1 inch (2.5 cm) long that cover the stems. Sparsely arranged, narrow, green leaves appear on newer stems, but fall from older ones, so that leaves are only found on the youngest parts of the plant. The plant blooms from spring into late summer, producing tiny, true flowers held in two bright red, fused bracts.
Crown of Thorns does well in even the poorest soil, provided it is well-drained and does not remain moist. It prefers a location in full sun but will tolerate some shade for a portion of the day. A tough plant, Crown of Thorns is a good choice for a seaside location with salt spray or soil with a high salt content. If you grow your Crown of Thorns as a houseplant, place it in a south- or west-facing, uncovered window, ensuring it receives maximum sunlight. Although the plant is drought tolerant, you can induce your plant to retain its leaves and bloom frequently by watering it regularly and giving it an occasional dose of fertilizer. Check fertilizer labels and choose a basic, balanced formula without added micro-nutrients, since the plant is sensitive to boron.
Crown of Thorns benefits from some light pruning as it matures. At the end of each growing season, remove some older, leafless branches to stimulate new growth in spring. Clear away dead leaves and any dropped, matted flowers to allow the soil to dry well and reduce the likelihood of fungal disease. If you notice any brown stems or leaves on your plant, cut these back to healthy tissue to prevent rot from spreading through your plant. If you grow your plant indoors and wish to move it outside in warmer weather, keep it in partial shade for a week or two until it acclimates to bright sunlight.
To produce new specimens from your Crown of Thorns, take cuttings from younger branches in spring or summer. To stop drainage of sap from the cut end, dip each cutting into warm water for a few minutes. Next, dry the cuttings for a few days, allowing a callus to form over the cut end. Insert the dried end of each cutting into damp sand, place in a shaded location either indoors or outside and wait several weeks, testing the cuttings periodically. When you feel resistance to a gentle tug, your cuttings have rooted and are ready to re-pot.
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