Crown of thorns can be shared
  Heat-loving plant is ideal for South Texas climate

June 16, 2005
Victoria County
Master Gardener

A friend gave me a plant that had been a cutting from a plant given to her by a friend. This started my interest in looking into other varieties of this plant that would bloom year-round but thrive with our extreme heat and bright sun, with little maintenance.

With its very easy propagation methods, it could provide a steady supply of plants for gifts, Master Gardener donated plant sales, as well as garden landscaping. During the winter this plant loses some leaves, but the spring season renews the stalks with dark green foliage. Local nurseries have several varieties of this plant called crown of thorns, which has become a favorite of mine.

After some 30 years of breeding selection by various professional and private enthusiasts, these plants are an exotic addition to any nursery's plant portfolio. They are a good selection for Southern gardens as they are incredibly heat tolerant. In fact, they are capable of thriving when temperatures are above 90 degrees. They will tolerate full sun and salt spray thus making for good container plants in our coastal climate flowering nearly all year.

They will, however, freeze. Crown of thorns can handle temperatures down to 30 degrees; too cool temperatures cause the stems to be mushy.

These plant characteristics are reason enough for my choosing the crown of thorns for container plants in my personal garden; however, I find the history of the plant and how it has been shared through time equally as compelling. The Internet proved to be a good source for research and identification of the wide varieties of this plant.

According to an article by Dr. T. Omrello of Union County College, the scientific name of crown of thorns is Euphorbia milii (formerly Euphorbia splendens.)

Where does this unfamiliar nomenclature come from? Euphorbia was the Greek physician of King Juba II of Numidia (present day Algeria.) about 50 BC to 19 AD. King Juba II was the first person to find a succulent-type crown of thorns, and he named it after his physician. Milii is for the name of Baron Milius, once governor of the island of Bourbon, who introduced the species into cultivation in France in 1821. Splendens means splendid. Such terminology has been shared through time in translation. Furthermore, it is said that substantial evidence exists that the species, native to Madagascar, had been brought to the Middle East before the time of Christ.

The crown of thorns is a woody, spiny, climbing, and sometimes vining, succulent shrub with shoots reaching a height of up to 6 feet. Leaves are found primarily on young growth. The plant flowers nearly all year; the actual flowers are small but the brightly colored modified leaves (bracts) found just beneath the flowers are what make the plant quite attractive.

A sticky white sap (latex) exudes from a cut to the plant and may produce a severe dermatitis on susceptible individuals and should not be ingested. The article referenced above goes on to say that the latex of some species has been used for arrow poisons and to stupefy fish for capture.

Euphorbias are not planted near stocked pools since the exudates from broken roots can be fatal to fish. Cats and rabbits might be susceptible to these plants; deer and cattle will not eat them. Despite its poisonous properties, the latex has been used for medicinal purposes in the past.

The original forms were mostly bright red in color; leaves were sparse and thorns were prominent. The newer cultivars have reduced thorns (actually more like ridges on the stem) and have large attractive leaves, existing in a range of colors from red, orange, salmon, pink, yellow and a creamy white, including bicolor bracts. They are relatives of poinsettias.

Newer releases from Thailand include some extremely large forms that can reach 3 feet in height and have leaves up to 12 inches in length. This hybrid is called Poysean, and large containers can handle the vigorous growth. Rock gardens can be used for a planting site for crown of thorns with low water requirement and full sun availability.

Even if all conditions are right, crown of thorns will sometimes flower poorly or not at all, especially in urban locations where perhaps lights on the plants at night (street or security) can disrupt their flowering cycle.

This plant family can be divided into two groups - the common, older types and the recently developed Thai hybrids. More than 2,000 varieties have been developed. The older types were developed by Humel in 1960 with the "giant crown of thorn" being most common. A newer Thai version is the compact-dwarf "Short and Sweet," which is excellent for use as ground cover, as well as the "Mini Bell."

Many varieties have increasing availability where some are sold as bare root. It takes 12 to 14 days for the bare roots to form fresh roots.

A few pests occur occasionally with crown of thorns and include scale insects, mealybugs, spider mites and thrips. Ants do not like the sticky substance on the stems. Disease is more common, and usually includes too much moisture with bacterial and fungal leaf spots, fusarium and rhizoctonia stem and root rots as well as botrytis flower blight. Yellow or dead foliage should be removed. The disease is more prone to develop with tools and equipment not being clean. A modest amount of rain is well tolerated but the dried flowers and leaves should be cleaned before periods of prolonged wetness. Watering at the bottom of stems is better than overhead due to water collecting in the flower heads.

The obvious pruning problem for crown of thorns is the toxic milky sap excretion, which should be kept out of eyes. A significant benefit to pruning is that cuttings can be potted and you will have other plants. Crown of thorns responds well to repotting, and, in fact, it is one of the few plants that can be repotted lower than the original soil level to enable additional cuttings to root.

A cutting should be at least 4 inches long (and longer if possible) to root properly and should be kept in a shaded area until rooted. A clean sharp knife should be used to take cuttings; use only inexpensive knives as the sap can ruin cutting edges. The cuttings can be allowed to dry for 24 hours before planting; rooting hormone powders could help the rooting progress. A dropped leaf may be successful in rooting or seeds taken from the flower will produce plants when care is given.

Seed propagation is usually done for developing cultivars with two different varieties being used. It will take five to eight months to flower with seed propagation.

Try this colorful, sun- and heat-loving plant in your garden landscape. I am certainly grateful for the friend who shared my first cutting from the friend who first shared this plant with her. Its many attributes could be the reason for the on-going nature of this beauty that has been shared for thousands of years.