Some species of trees protect themselves from predators with sharp, dangerous spines that discourage damage to their trunks, branches or other structures. While spiny trees may be attractive landscape specimens or bear enticing fruit, they can be dangerous to young children or unwary pets. If you do choose to grow them, be mindful of the dangers as well as the perks, and try to prune so that potentially harmful branches are out of reach to very small kids.
Hawthorn (Crataegus spp.) trees and shrubs boast thorny stems along with bright fruits, good fall color and showy flowers in early summer. Hawthorns can grow fairly tall and in a wide range of climates. Washington hawthorn (Crataegus phaenopyrum), for instance, is hardy in U.S. Department of Agriculture plant hardiness zones 3 through 8, and can grow to heights of 30 feet. Beware this beautiful tree -- a scratch to the eye from one of its sharp, large thorns, can cause blindness. Used medicinally in some parts of the world and as home remedies, the berries effect blood pressure and heart rate. Native Americans often used the berries for the dried fruit mixed with venison and fat in their pemmican. The edible leaves are sometimes used in salads. The fruit attracts a variety of wildlife. Hawthorn symbolizes hope in various cultures, and according to legend, is favored by fairies.
Unlike other species of thorny trees, holly (Ilex spp.) wears its spines on its leaves rather than its branches. Though the number and severity of spines depends on the species, most types of holly have at the very least, a sharp or pointed leaf tip. Holly leaves and berries are mildly toxic to humans, dogs, cats and horses. A popular variety, English holly (Ilex aquifolium), thrives in USDA zones 7 through 9 and displays dark green, glossy leaves between 1 and 3 inches long. These leaves are conspicuously toothed, containing many pointed spines along both sides of the pinnate leaf. While holly’s flowers are inconspicuous, its red berries are among its finest features and are often used in winter holiday decorations.
Native to North America, handsome mesquite trees (Prosopis spp.) with their reddish brown trunks also have long thorns, up to 1 inch in length and very sharp. Mesquite likes sunny and arid areas, and it is among the most common of small trees in the deserts of the Southwest. It is mostly the drooping, lower branches on a mesquite’s trunk that contain the thorns, while the smooth trunks have no thorns. Chilean mesquite (Prosopis chilensis) is thornless and hardy in USDA zones 8 through 11. Mesquite can cause colic in horses, but is not known to be toxic to humans, dogs or cats. The seedpods are enjoyed by wildlife.
In Spanish, palo verde means green pole. Some of the palo verde (Parkinsonia spp.) trees have yellow-green bark, leaves and flowers, while others have blue-green bark. Palos verde is a member of the pea family (Fabaceae). Little leaf palo verde (Parkinsonia microphylla syn Cercidium microphyllum) is hardy in USDA zones 8 through 9. Growing to heights of 35 feet, it has a rounded canopy with thorny branches and lacy foliage. It prefers full sun conditions, moist to dry soil, although it is intolerant to prolonged drought, and alkaline soil with sand or loam. Their persistent winter pods, between 1 and 3 inches long, produce seeds that can be cooked and eaten like edamame or peas when harvested from the tree not the ground. Palo verde is a nurse tree in the desert, providing nutrients and habitat to plants and animals. Its attractive green trunk makes it also popular in urban landscapes.