The Ephemeral Trellis

When I started developing my vegetable garden I had little biomass handy for various projects beyond a modest stream of goat manure. Gradually support species established, and now I have more than I can use. One especially valuable plant is bamboo, which I am steadily learning to use for various projects. Today I made a bamboo trellis using zero string or fastening.

A typical approach for growing climbing crops in this industrial age is to put in a few star pickets (T-posts in the USA) then string some wire mesh between them. Then when the crop is finished you face the horrible job of taking the rusting, tendril infested mess down again (or leaving it until it becomes a hazard).

What most people never stop to consider in this time of overabundance is the resource consumption of that simple construction. The early industrial revolution was primarily a transformation in the production of iron- that essential ingredient in civilised life for thousands of years. Up until that point vast amounts of forest were cut in rotation to make charcoal, essential for smelting iron ore. That made iron so valuable that it could only be used for hand tools, weapons and fasteners. The idea of using iron for structural purposes like roofing and fences would seem absurdly extravagant. Tapping into vast coal reserves upended that equilibrium, and the rest is modern history.

One single bed in my vegetable garden is about 10 m long, needing six star pickets and an equivalent length of wire (double if I couldn’t be bothered training the vines up). I would estimate the structure would contain about 40 kg of iron, which has an embodied energy of about 20 megajoules per kilogram, for a total of 800 megajoules of embodied energy. That is equivalent to 80 days of food energy for a human. Industrial yield maize produces 10 days’ worth of calories from the same bed each year, climbing beans much less. The iron would rust long before it could break even in terms of energy invested.

Another way to visualise the situation is that it takes 45 kg of dry wood to make 15 kg charcoal to produce 1 kg of iron, so the iron used in my simple trellis would represent 600 kg of charcoal and 1800 kg of dry wood. The meagre dollars we spend in this age on these resources are shockingly disconnected from the true value of the materials.

Funnily my biggest issue with using structural metal in my garden comes from me being lazy. I always put off removing it until it becomes a rusting mess. I have many meters of goose fencing tangled in the weeds I have to extract and dispose of one day. All that metal is a resource that never had a chance of repaying the energy invested.

To address these glaring issues I have learnt to make simple trellises from bamboo. Not bamboo plus string or wire. Just bamboo and nothing else, using a few simple hand tools (the production of which should be sustainable in some form on the far side of this time of industrial excess). A word of caution- bamboo can be deceptively sharp when cut, as can the tools used to handle it. Gloves and caution are advised at a minimum. Bamboo is quite unlike wood in its strengths and weaknesses, and unfortunately Australia has little culture in its use to tap into, so I have mostly had to figure things out by bits and pieces.

The basic technique is as follows. I cut second or third year stems (which thicken and strengthen after their first season) using a small folding saw. For this project I worked with Bambusa chungii, a beautiful silver stemmed clumping species. Different species vary in their dimensions and properties. The leafy tops go to the goats, then I use a bamboo hatchet to knock off the remaining leaves. The lowest, strongest sections are cut to a bit over my height, then driven into the ground in a straight row using a fence post driver about 1-2 m apart. Pay attention to the stem as you go since occasionally they will splinter during the process. Remove these duds and try again. Be sure to leave a node at the top to reduce the chance of splitting.

Next I use the bamboo hatchet and a handy chunk of wood to split the upright posts down to about 30 cm from the ground (ideally a node will prevent the split going all the way down). The splits must be aligned with the bed. Then I take the thinner middle sections of the stems and split them using a bamboo splitter (though you can do this with the bamboo hatchet instead). Tapping with a chunk of wood helps. I try to make these slats as long as possible, so I can insert them horizontally into the split the uprights without joins, but overlaps aren’t that much of an issue.

To add the next horizontal spaced higher than the first I split the uprights into quarters, giving me the ability to improvise crossing them over. Just use one quarter at a time so there are others flexible enough to work for the next level up. I add more horizontals until I run out of vertical space.

The resulting structure works well for chunky vines like sword beans (which I intend to plan here) and large seeded lima beans (which I should plant soon if I can hop to it). Yams and angled luffas also do well. I normally get one or two seasons out of it before it starts to slump.

Best of all, when the garden has inevitably moved on and the weeds have returned the space to fallow all I have to do is give the structure a gentle shove and it turns into a modest pile of kindling, or if I am too lazy to make use of that it will completely disappear given another year.

Humans are masters at improvisation, but you cannot build a bamboo trellis unless you grow the bamboo first and take the time to learn how to use it. Then you to can begin your slow journey to break your reliance on “cheap” industrial inputs.