A trellis is a supportive framework that allows vining plants to grow vertically, maximizing garden space and enhancing the aesthetics of a yard. Growing plants upward offers several practical benefits, including improving air circulation around the foliage, which helps to prevent common diseases like powdery mildew. Vertical growth also keeps fruits and vegetables off the ground, resulting in cleaner harvests and reducing losses to pests. Selecting the correct structure depends entirely on understanding how different plant species physically attach themselves to a support.
How Climbing Plants Attach to Supports
Climbing plants utilize distinct biological mechanisms to ascend, which dictates the type of trellis they need.
One common method involves stem twiners, where the main growing tip wraps its entire stem around a support, spiraling clockwise or counter-clockwise depending on the species. Plants like pole beans and wisteria are examples of strong stem twiners that seek out and coil tightly around vertical elements.
Another method uses tendrils, which are specialized, slender organs sensitive to touch. Tendrils are often modified leaves or stems that reach out and, upon contact, quickly coil into a helix, shortening and pulling the plant closer to the support. Peas use tendrils modified from their leaves, while grapes and cucumbers use tendrils that are modified shoots to grasp wires or thin bars.
Some vines are adhesive climbers, employing root-like structures that cling directly to flat surfaces rather than wrapping around a frame. English ivy and creeping fig (Ficus pumila) produce adventitious roots that secrete a sticky, cement-like substance containing polysaccharides and proteins to bond firmly to masonry or wood. These plants do not need an open trellis structure, but rather a solid wall to which they can adhere.
The final category includes scramblers or leaning climbers, such as climbing roses, which lack specialized organs for self-attachment. These plants rely on stiff canes and sometimes thorns or prickles to hook onto neighboring plants or structures for support. Scramblers require the gardener to manually weave and tie their stems to the trellis to maintain vertical growth.
Ornamental and Flowering Trellis Plants
Many popular flowering vines are grown for their visual impact, using various climbing mechanisms to cover structures with color and fragrance.
Clematis
Clematis is often called the “Queen of Climbers” and employs twining leaf petioles (leaf stems) to wrap around slender supports. Because these leaf stems are not particularly long, Clematis vines require thin supports, ideally less than half an inch in diameter, to successfully wrap and climb.
Wisteria
Wisteria is an extremely vigorous and woody twiner, known for its dramatic, fragrant hanging clusters of flowers in spring. Its powerful stems wrap so tightly that they can eventually damage or crush lightweight wooden trellises, requiring a very robust structure like heavy-gauge steel wire or solid timber beams for support. Proper training involves guiding the main stems horizontally to encourage more flowering spurs.
Climbing Roses and Annuals
Climbing Roses are technically scramblers and do not climb on their own, instead relying on gardeners to tie their long, stiff canes to a support. To maximize the production of flowering side shoots, the main canes should be trained to grow horizontally or at a 45-degree angle across the trellis. Annual vines like Morning Glory are delicate twiners that quickly cover a temporary structure with trumpet-shaped flowers during the summer months.
Edible and Productive Trellis Plants
Trellising food crops is an effective method for increasing yield in small spaces and protecting the harvest from pathogens.
Cucumbers and Grapes
Cucumbers and Grapes both use sensitive tendrils to anchor themselves, making them well-suited for trellises with thin elements like wire or string. Cucumber tendrils coil into a double helix, which acts like a spring to absorb tension and pull the vine upward as it grows. Grapes develop woody stems over time, requiring a sturdy wire or post system to support the weight of the mature vines and heavy fruit production.
Pole Beans
Pole Beans are classic twiners that quickly spiral up any vertical support, often reaching heights of 10 to 15 feet. Since they are annuals with relatively low weight, a simple teepee or a structure made of twine or narrow poles is often sufficient to bear their load. The benefit of trellising beans is that it keeps the pods straight and clean, which is especially desirable for varieties grown for fresh eating.
Peas
Peas are cool-season crops that use delicate leaf tendrils to cling to supports, making netting or brushy branches the most effective type of trellis for them. Gardeners must ensure the mesh size is small enough for the tendrils to grasp, typically around two inches wide, to prevent the plant from collapsing under its own weight.
Matching the Plant to the Trellis Structure
The longevity and strength of the support must correspond directly to the plant’s mature size and climbing style to prevent structural failure.
Heavy, permanent twiners like Wisteria or the woody stems of mature Grapes require structures made from robust materials such as galvanized steel wire tensioned between heavy posts. These plants exert considerable force as their stems thicken, making inadequate supports a hazard.
For tendril climbers like cucumbers and peas, the trellis should incorporate thin, easily grasped elements, such as agricultural netting, string, or narrow wooden laths. Clematis, with its short leaf petioles, will also fail to climb a trellis with thick, widely spaced bars, so a structure with a thin mesh or wire grid is necessary.
Scramblers, including climbing roses, need a strong, rigid frame like a wooden lattice or metal arch to which their canes can be securely tied with soft plant ties or twine.
Adhesive climbers like ivy do not need a three-dimensional trellis, but rather a flat, solid surface like a wall or fence for their aerial roots to attach. Using a solid surface structure eliminates the need for manual tying, but gardeners should be aware that the adhesive roots can sometimes damage soft materials like mortar or painted wood.