How do you care for a potted crown of thorns (Euphorbia milii) these days?
Crown of thorns is also known as iron begonia, unicorn thorn, unicorn flower, etc. It is a sprawling shrub plant of the genus Euphorbia in the family Euphorbiaceae, native to Madagascar, Africa, and widely cultivated in the tropics and temperate zones of the Old World. It is cultivated in both northern and southern China, commonly seen in parks, botanical gardens and courtyards. It has extremely high ornamental cultivation value. Let us take a look below at how to care for a potted crown of thorns!
Growth habits of crown of thorns
Crown of thorns prefers a warm, humid environment with plenty of sunlight. It tolerates shade slightly, but fears high temperatures. It is fairly drought-tolerant and not cold-hardy. A loose, well-draining leaf mold soil is best. If the temperature is relatively low in winter, it shows a short period of dormancy. Crown of thorns has many horticultural cultivation types, among which the one with yellow-white bracts is rather special and is cultivated in very few places in China.
Propagation methods for crown of thorns
Crown of thorns is mainly propagated by cuttings. Cuttings can be taken throughout the entire growing period, but May to June is best, giving a high survival rate and the easiest rooting. Choose thick, sturdy branches about 10 cm to 15 cm long (with 3 to 4 leaf nodes), wipe away the white sap flowing from the cut, coat it with plant ash, and let it dry in a cool, shady place for 2 to 3 days. Once the wound is dry, insert it into plain sand, water thoroughly, then water sparingly afterward, watering again only when the potting soil is slightly dry. After about 50 to 60 days it will be able to root.
How do you care for a potted crown of thorns?
1. Soil: The substrate used for potting crown of thorns can be garden soil : furnace slag = 3:1, or garden soil : medium-coarse river sand : sawdust (mushroom residue) = 4:1:2, or one of paddy soil, pond mud, or leaf mold, or peat + perlite + ceramsite = 2 parts + 2 parts + 1 part, or garden soil + furnace slag = 3 parts + 1 part, or peat + furnace slag + ceramsite = 2 parts + 2 parts + 1 part, or sawdust + vermiculite + medium-coarse river sand = 2 parts + 2 parts + 1 part.
2. Potting: When potting small crown of thorns seedlings, first place a 2 to 2 cm thick layer of coarse-grained substrate or ceramsite at the bottom of the pot as a drainage layer, sprinkle a layer of fully decomposed organic fertilizer on top as a base fertilizer, about 1 to 1 cm thick, then cover with a layer of substrate about 1 to 1 cm thick, and then place the plant in, so as to separate the fertilizer from the root system and avoid burning the roots. After potting, water thoroughly once and keep it in a slightly shaded environment for a week.
3. Watering: Crown of thorns is a succulent plant and is drought-tolerant, so it should not be watered too much. If the potting soil stays too wet for a long time, it will not only cause root rot but also endanger the plant's survival, so normally water just enough that the potting soil stays slightly dry. In summer, water evaporates quickly, so water a little more appropriately, but there must be no standing water in the pot. Excessive watering during the flowering period will cause flowers and buds to drop, and may even cause root rot.
4. Fertilizing: Crown of thorns should be fertilized lightly, applying a thin fertilizer 2 to 3 times each spring. Fertilizing can be reduced in autumn. It does not like concentrated fertilizer; during the growing period, applying decomposed dilute cake fertilizer water once every 3 to 4 weeks is enough. Excessive fertilizing, especially too much nitrogen fertilizer, makes the branches grow leggy, producing only leaves and no flowers. Adding 1 to 2 applications of phosphorus and potassium fertilizer during the bud stage makes the flowers more numerous and brightly colored.
5. Light: Crown of thorns likes plenty of sunlight and should be given fairly ample light in all four seasons. During the flowering period, with ample sunlight, the bracts are brightly colored and the flowering period is long. With insufficient sunlight, the flower color is dull, and if kept in a shaded condition for a long time it will not bloom or will bloom very little. It likes warmth and is not cold-hardy. In northern regions it is generally taken outdoors in early May, placed in a sunny spot, and brought indoors in early October, placed in a spot indoors that gets sunlight.
6. Temperature: During overwintering, when the room temperature is low, the leaves of crown of thorns drop completely and it enters a semi-dormant state. At this time, watering must be strictly controlled and the potting soil kept dry. When the temperature is below 0°C, the plant will die from frost damage. If the winter room temperature can be kept above 15°C, it will bloom continuously throughout the winter. Crown of thorns is an indoor flower very suitable for planting in the north in autumn and winter.
7. Pruning: Crown of thorns blooms at the tips of new branches. To make crown of thorns bloom more, proper pruning must be carried out. Because if the main branches are too long, there will be fewer flowers. So after the flowering period, the overly long and irregularly growing branches should be cut short. Generally, 2 new branches grow below the cut on the branch, and when the new branches grow to 5 to 6 cm they can bloom. Prune once a year, and after a few years the whole plant will be covered with bright little red flowers.
8. Pests and diseases: During the rainy season, when there is a lot of rain, high air humidity, and the surface of the potting soil is not clean, crown of thorns is prone to root rot and stem rot. Root rot can be treated by drenching the roots with Root Rot Ling, and stem rot can be treated by spraying the stems with agricultural streptomycin or Liku Jing. The main pests of crown of thorns are whiteflies and scale insects. Whiteflies can be treated by spraying Puji Ling or thiamethoxam, and scale insects can simply be caught by hand.