Thorns on fruit trees are a defense mechanism to defend against grazing animals, such as deer and livestock, whose eating habits may damage or even destroy a tree. Young fruiting plants in particular develop thorns for protection. Once well established, however, the thorns become fewer, which makes harvesting easier and less painful for growers.
Lemon trees (Citrus limon) and lime trees (Citrus aurantifolia), which tend to grow in U.S. Department of Agriculture plant hardiness zones 8 through 11, have sharp thorns on their twigs. The Lisbon (Citrus x limon) is a particularly thorny and vigorous variety of lemon tree commonly grown in zones favorable to citrus cultivation. Easy to maintain and resistant to heat and frost, it has dense, spreading foliage that produces fruit year round. Mexican lime, also known as key lime, is a thorny shrub-like, tree with fragrant flowers and small, greenish-yellow fruit that reaches maturity in the fall and winter. Thornless varieties are available, but they typically produce less fruit. Selections of grapefruit and orange trees also produce foliage with thorns.
Pomegranate (Punica granatum L.), though not commonly thought of as such, is a berry plant, and it produces thorns. The pomegranate tree grows in USDA plant hardiness zones 7b through 10 as a small, long-lived tree or bush with moderately thorny branches and red-orange blossoms. The fruit may be yellowish-brown or purplish red when ripe, depending on the cultivar, and contain many edible bright pink or red seeds.
Prickly pear (Opuntia humifusa) has pads bearing sharp spines that are not technically thorns but stems. Sometimes referred to as nopales, prickly pears are also covered in tufts of short, hair-like spines. Its edible fruit is commonly used in the Southwest and Mexico for making jams and candy. It also may be eaten peeled and sliced with a squeeze of lemon. Prickly pears are easy to grow in dry, sandy soil that requires little water or nutrients, in USDA plant hardiness zones 5 through 10.
The hawthorn (Crataegus spp.) is a small, bushy tree that produces a bright red berry-type fruit in USDA hardiness zones 3 through 9. Despite the long, sharp thorns on its branches, this plant is often used as a garden ornamental due to its lush foliage. Its fruit, known as haws, is more popular with animals than humans as a food source; however, it is commonly used in teas and jams.
- California Rare Fruit Growers: Pomegranate
- University of California Riverside: College of Natural and Agricultural Sciences: Citrus Variety Collection: Frost Nucellar Lisbon Lemon
- Purdue University Horticulture and Landscape Architecture: Lemon
- University of California Riverside College of Natural and Agricultural Sciences: Citrus Variety Collection: Mexican Lime
- University of Florida School of Forest Resources and Conservation: Florida Forest Plants: Pricklypear
- University of California Agriculture and Natural Resources: UC IPM Online: How to Manage Pests: Pests in Gardens and Landscapes: Hawthorn
- University of Florida School of Forest Resources and Conservation: Florida Forest Plants: Hawthorn
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