Thorny plants grow the sharp and often painful spikes for their own protection, but they can also protect your home. Strategically placing plants that grow thorns in your landscaping can discourage would-be burglars from reaching your home without some serious scratches. But if you have kids or pets, knowing which plants have thorns is also important for safety reasons to prevent injuries.
Basics of Thorns
Thorns are sharp pointy projections from the branch of a plant. The purpose of the thorns is to protect the plant from being eaten by a local herbivore. Species with thorns often have showy flowers or bright berries on them, so they look attractive while packing a painful punch.
The list of plants with thorns suitable for landscaping purposes is extensive and includes broadleaf evergreens, perennials, deciduous shrubs and trees. These species include many types non-native to North America but adapted to some of the U.S. Department of Agriculture plant hardiness zones.
Trees With Thorns
Hawthorn trees have a reputation for possessing sharp thorns on their branches. Species such as the Ontario hawthorn feature horizontal limbs armed with 2-inch spines. Pruning these trees becomes difficult due to the thorns, but hawthorns offer spring flowers and excellent fall color as a rule, making them worth the effort.
Other trees with thorns include the honey locust, Osage orange and the wild plum, which are all native types. Non-native thorny species include the common jujube tree and the harigiri, a tree growing between 40 and 60 feet, used as a shade or specimen tree. It has thorns on its trunk when immature.
If you have trees with thorns in in your landscaping, you can prevent injury by pruning the thorn-covered branches above head level. Plants like the immature harigiri tree with spikes on their trunks are more difficult to manage in the landscape.
Thorny Perennial Plants
Mountain thistle, a shrubby perennial plant, grows in zones 7 through 10. Its leaves have spines and its flowers, resembling those of snapdragons, are pinkish red. Mountain thistle grows in many soil types but not in waterlogged areas.
Thorns are present on perennials such as the globe thistle, prickly pear and sea holly. Sea holly has spiny flowers shaped like eggs. They're purple-blue and bloom all summer. The asparagus fern is not a true fern but this perennial has evergreen foliage and small thorns.
Deciduous Shrubs With Thorns
Thorny shrubs make a good barrier around your home as a security feature. Many types of thorny bushes can be trimmed into a hedge. They often bloom with pretty flowers to add curb appeal to your home, making this security component attractive and functional.
One aspect of the numerous varieties of deciduous shrub roses available for landscaping is their spines. These plants come in many sizes, making them a versatile landscaping option. The Lutea cultivar of the banksia rose, for example, grows to 20 feet high, while the Chewground type of shrub rose can be 12 inches tall.
Other deciduous shrubs with thorns include raspberry bushes, hardy orange, Japanese barberry, Chickasaw plum, Chinese matrimony vine and the scarlet firethorn. The hardy orange has extensive, sharp thorns, making it fit as a barrier plant or hedge in USDA zones 5 through 9.
Other Thorny Plants
Annuals such as the spider flower of South America and the prickly poppy from the western United States have thorns. Broadleaf evergreen species such as the pigeon berry and citrus lemon are other thorny plants landscapers value for their foliage, flowers and fruiting ability.
Some vines, including bougainvillea and the sarsaparilla plant, have thorns, as well. Bougainvillea has its thorns along the stems where the leaves grow out. These vines are suitable only for USDA zones 9 through 11 if kept outside, but they work as greenhouse or sun room plants in colder areas.
John Lindell has written articles for "The Greyhound Review" and various other online publications. A Connecticut native, his work specializes in sports, fishing and nature. Lindell worked in greyhound racing for 25 years.