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Ligustrum is a genus of plants that contains about 50 flowering shrubs and trees belonging to the Oleaceae (olive) family. However, all species of ligustrum are now more commonly known as privet. Since ligustrums are either evergreen or deciduous (semi-evergreen), they are popular in residential and commercial landscaping designs. In fact, as the common name suggests, they offer excellent privacy hedging and sound screening. For this reason, many varieties of ligustrum are simply referred to as privet hedges.
Ligustrum represents a hardy and diverse group of plants that originate from Europe, Asia, and North Africa. However, they also range in naturalization from China to Japan and the Himalayas. In the U.S., many species of ligustrum have become naturalized to the point of being invasive. In fact, after the introduction of common privet (Ligustrum vulgare) in the 1700s, excessive cultivation eventually permitted many varieties to successfully compete with and replace native vegetation. As a result, L. vulgare is now naturalized in the northern U.S., while Chinese and Japanese privet are abundant in the Midwest and southeastern U.S.
Although ligustrum is invasive in the U.S., it is considered an obnoxious weed in New Zealand. In fact, excessive naturalization has led to serious consequences for those with asthma and eczema, two conditions known to be associated with the pollen of this genus. For this reason, the sale and cultivation of ligustrum is barred in New Zealand. Residents affected by its spread are encouraged to contact local authorities to have it removed.
Birds consume the berries of these shrubs and then deposit the seeds elsewhere, contributing further to the spread of ligustrum in many regions. The foliage of privet is also a favorite food of several insects, such as whiteflies, spidermites, and aphids. However, ligustrum is toxic to other living creatures. For instance, the berries and foliage are poisonous to horses. Some species of ligustrum are mildly toxic to humans.
Most varieties of ligustrum may be propagated by cuttings and, of course, by seed. They are fast growing plants, increasing in height an average of 25 inches (63.5 centimeters) per year. For this reason, most species require diligent pruning to maintain their shape and to prevent spreading. In addition, ligustrum can tolerate nearly any soil type and environment, including high heat, extreme cold, and drought. However, these shrubs cannot endure consistently wet soil.
Ligustrum varieties present a range of color in their oval-shaped foliage. Silver Star, for instance, produces greenish-gray leaves with silver edges, while Tricolor starts out with pink leaves that later turn to variegated green and white. The flowers of the ligustrum genus are small and white and appear in late spring and early summer. However, while the flowers are attractive, they give off an odd odor, which many people find unpleasant. It should also be noted that the berries, which range in color from dark blue to black, produce a juice that can stain walkways and driveways.