Proper trellis material is critical for successful mirliton growing. For decades, “backyard mirlitons” were grown vertically on the common “chain link” fence with 12 gauge, (1/8th inch) wire. With the advent of the wooden “security fence”, home gardeners lost their built-in trellis. Moreover, research demonstrated that mirlitons fruit more prolifically on horizontal trellises, growers searched for alternative trellising. The problem was that those old chain link fences held a secret: the wire was the perfect diameter for mirliton tendrils. When growers used chicken wire, lathe, bamboo poles, plastic mesh etc. the results were not good. If trellis materials are too large in diameter, the tendrils will not hook and coil and the plant will not grow and extend vigorously; the same is true for materials too small in diameter.
Mirlitons are herbaceous climbers that, in addition to leaves and flowers, have separate tendril structures that branch out in two to five smaller branches. These are slender, string-like coiling climbing organs that are sensitive to contact stimuli. When they come into contact with the correct diameter object, they coil around the object to provide support for the main stem and subsequent fruit. The tendril coils tightly around the anchoring object and coils backward to the plant, creating both an anchor and a spring-like coil. This secures the plant against wind—allowing a little sway—and holds up the stem when fruit begins to weigh it down. Mirliton tendrils are strong but delicate and do not regrow once damaged.
Although the signaling mechanism is not entirely understood, my observation is that when tendrils hook onto a support structure and exert tension on the stem, the meristem (stem tip) is stimulated to grow and extend. A mirliton stem can grow more than 20 feet and the more stem growth means more fruit production. If a stem is grown on a horizontal trellis or arbor with supports that are too large in diameter for the tendril to wrap around, instead the tendrils will coil unattached in the air and stem growth will slow if not stop completely. In a sense, the plant only extends to areas that can provide support and tendrils extending in front of the stem probably exert tension on the main stem and signal the direction of stem growth and increase meristem (stem tip) extension. Improper trellis material that does not provide structures for tendrils to hook and coil on can result in stunted plants and stem breakage from wind or fruit weight.
The trick with trellising—and it is a simple trick—is to use trellis support materials that tendrils can easily and readily attach to. That means first providing the vine with support to climb vertically. This is best done using “tomato cages” which are typically constructed of 1/8th inch galvanized wire and then providing string supports to the overhead trellis, using a 3-strand poly twine that is at least 1/8th inch diameter. If you don’t have room for a horizontal trellis, then any wire fencing 12 gauge or thicker will work fine. The mesh size is not important since the fruit will hang on the side of the support structure.
Horizontal trellises need the same minimum wire size. For decades, Louisiana mirliton growers have used overhead trellises with a solid wood framework (4x4 posts and 2x4 rails) covered with “goat fencing” or similar fencing material. Goat fencing is galvanized steel 4” x 4” square pattern fence mesh that is hinge lock woven. The hinge lock makes it easier to work with than welded fence and the 4 mesh is large enough for fruit to drop through and hang below the trellis.
The key is that the wire is at least 12 ½ gauge, (2.5 mm or approximately 1/8th inch). Tendrils do not hook and anchor well on string or wire with diameters less than 1/8th inch. I recently saw a string trellis that used 1/16th inch string and the tendrils refused to hook to it. From an evolutionary perspective, the plant is searching for structures that can support it from wind sway and fruit load; a small twig won’t work and a large branch won’t permit a tight coil. What we have laying around the yard might look like a good trellis idea (PVC pipe, bamboo, old 2x4s), but your mirliton might not agree.
There are many trellis material options other than galvanized fencing. Many growers use heavy concrete reinforcing mesh which is sold in panels, not rolls, and can often be found in recycling centers. It has a 6”x6” square mesh and is a thicker 9 gauge which tendrils appear to respond well to. Always be careful to bend in sharp end pieces to avoid accidents (masking tape works remarkably well in blunting end cuts). Also, keep in mind that long stems and plenty of trellis space ensures that leaves are exposed to sun and air circulation which inhibit plant diseases and insect infestations.
Finally, one of the most important steps in trellising is augmenting the vertical path so that new lateral shoots from the bottom of the plant have a pathway to the top since each one of these shoots means more fruit production. It is also important to keep lateral shoots from contacting the ground since soil-borne fungi are transmitted to leaves and although the ground stems will bear fruit, they are more susceptible to insects. This means that as new lateral shoots emerge, tie thick poly twine to the wire cage at the base and connect it to the overhead trellis at an angle and pull the string taught. Then gently wrap the new shoot once or twice around the string so tendrils will hook and the shoot has a separate path to the top of your trellis. When a plant begins to grow vigorously there may be a need to add multiple string paths to spread out the plant at the top and avoid stems from falling over due to their own weight.
If you have any question about the appropriateness of a trellis material, simply watch the plant closely and note if the tendrils are hooking and coiling around the material properly. You will find several photographs of properly constructed mirliton trellises on our web site on the “Mirlitons 101” Picasa photo site by googling for Mirlitons.org