Shrubs that feature sharp, pointed structures on their stems are a common sight in many landscapes, serving both decorative and functional purposes. While people often use the term “thorn” to describe any sharp projection, this generalization overlooks distinct botanical differences in how these protective features develop. Understanding the precise nature of these sharp points is helpful for gardeners, providing insight into the plant’s structure and maintenance requirements.
Understanding Sharp Plant Structures
Botanists classify sharp plant structures into three categories based on their origin within the plant’s tissue. True thorns are modifications of a stem or branch, containing vascular tissue that connects them directly to the plant’s core structure. Because they are deeply embedded, thorns are difficult to detach without damaging the plant itself. A spine, by contrast, is a sharp point that evolved from a leaf, stipule, or part of a leaf. Spines are often found in arid environment plants, where they help reduce water loss.
The third category is the prickle, which is merely an outgrowth of the plant’s epidermis, or outer layer, and the cortex beneath it. Prickles lack the internal vascular tissue found in true thorns and spines. This difference means prickles can be detached more easily from the stem without tearing deep into the wood.
Common Thorny Shrubs for Landscapes
Many popular garden plants rely on these sharp structures for their defense, security, and appearance. The rose bush possesses prickles that grow irregularly along its stems, making it an effective barrier plant. Similarly, the canes of raspberries and blackberries, valued for their edible fruit, are covered in these same epidermal outgrowths. These plants are often used to create dense, deterrent hedges around property lines.
The Japanese barberry (Berberis thunbergii) is a widely planted ornamental shrub, valued for its bright autumn foliage. This plant features sharp spines that grow along its branches, which are modified leaves, making it a formidable barrier. Firethorn (Pyracantha) is covered in true thorns (modified stems) and is frequently trained against walls for its white spring flowers and colorful autumn berries.
Hawthorn shrubs (Crataegus species) are known for their dense growth habit and sharp thorns, which are modified branches. These true thorns are long and rigid, making hawthorn an excellent choice for a robust security hedge. Bougainvillea, often grown as a shrub in warmer climates, also has strong, curved thorns that help the plant latch onto supports as it climbs.
Biological Reasons for Plant Defenses
The development of these sharp structures increases the plant’s survival rate. The primary biological function is defense against large grazing herbivores, such as deer or livestock, that might otherwise consume the plant’s leaves and stems. By making the process of eating painful or difficult, the plant redirects animals to less-protected vegetation. This physical defense acts as a mechanical deterrent, working instantly upon contact.
Certain sharp structures also assist the plant in managing its environment. The dense covering of spines on some desert shrubs helps shade the stem, reducing surface temperature and minimizing water loss through evaporation. For climbing plants like Bougainvillea, the rigid, hooked thorns provide physical support, allowing the plant to grip and ascend vertical surfaces in pursuit of sunlight.
Safe Handling and Pruning
Working with shrubs that possess sharp structures requires careful planning and the use of appropriate protective equipment. When pruning, use long-handled tools, such as loppers or hedgers, to increase the distance between the gardener and the sharp points.
Pruning should be done with clean, sharp bypass shears to make precise cuts that heal quickly, reducing the risk of disease entry. When removing branches, cut them back to a point just above a healthy, outward-facing bud or to the main stem.
Strategic landscape placement is also a major consideration. Shrubs with sharp structures should be sited away from high-traffic areas like sidewalks or doorways. Placing these plants under windows or along property lines can take advantage of their natural ability to serve as security barriers.
When handling thorny shrubs, protective gear is necessary:
- Puncture-resistant gloves, typically made of thick leather or Kevlar, that extend past the wrist to shield the forearms.
- Long-sleeved shirts.
- Eye protection to prevent scratches and eye injuries from snapping branches.