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Barbara Hughes
Seminole County Extension Services Manager
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Sanford, FL  32773
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Extension Services

silverthorn: a tree for your landscape

Al Ferrer
Seminole Co. Residential Horticulturist

Silver Thorn is a small tree native to China and Japan and related to the Russian olive. This tree is well-adapted for landscape use in Florida because of its tolerance to low temperatures, drought and attractive leaves with shiny, dark green color on top and silvery color on the bottom. The tree blooms in the winter producing clusters of small, ivory-white, fragrant flowers, which are hard to find among the leaves. The reddish-brown fruits are edible and especially attractive to birds. Fruits are rare most of the year probably due to the constant pruning to control the growth of this tree, and flowers only grow in branches that developed the previous year.

The plant: The tree grows to about 15 feet tall with clumping stems and producing long irregular branches that gives the impression of disorderly growth. The young stems and leaves are covered with white scales that give a silvery color to the underside of the leaves and copper-colored scales give the appearance of dots to the plant surfaces covered with the scales. The individual flowers are small, about ? inch long, white but dotted with the copper colored scales. Flowers are fragrant, similar to that of gardenia. The flower has no petals and the structure is really an enlarged calyx, showing four sepals alternating with four stamens attached in the inner section of the sepals by a small filament. There is one pistil or female organ that contains one egg and forms one seed at the base of the flower. The fruit is small, about ? inches long, retaining the calyx remains as it grows. The fruit is edible, can be acidic or sweet, is suited for human consumption and is very attractive to birds. Most years there is little fruit production, but during some years the fruit production is fairly abundant.

Culture: Silver Thorn grows well in full sun or partial shade and will tolerate low as well as high temperatures very well. It will grow in most soil types requiring watering only until the plant becomes established. No additional irrigation is generally needed after that. Fertilize once a year, preferably in the spring after the plant produces new shoots. Propagation is by seeds or stem cuttings. In mass plantings space plants 5 to 8 feet apart. Keep scale insects under control with oil sprays as needed. Spider mites may be present during dry weather. Magnesium deficiency is also common on this plant under high pH conditions; if symptoms appear, correct pH levels by adding organic matter or other acidifying amendments to the soil.

Varieties: There are several cultivars available: ?Aurea? has leaves with yellow margins; ?Fruitlandii? has rounded undulate leaves; ?Maculata? has green leaves with yellow center; ?Simonii? has large leaves with silvery undersides, variegated pink and yellow; and ?Variegata? has leaves with yellowish-white margins.

Use: It is highly recommended as a hedge but requires frequent pruning because of its rampant growth. Silver Thorn is highly tolerant to saline conditions and can be used in areas with salt intrusion problems. It is also used in foundation plantings, screen and accent planting. Because this plant tends to sucker, it is used for stabilization of soils and banking. It has been used in the highway medians where the plants provide an effective divider between opposing lanes of traffic. But, the fruit produced by this plant represents a hazard to fruit eating birds that are killed in large quantities by oncoming traffic during the time of the year when fruits are available.

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