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nafex - Re: [NAFEX] Q about metal trellises and why they don't burn plants in the searing summer heat

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  • From: Douglas Woodard <dwoodard@becon.org>
  • To: North American Fruit Explorers <nafex@lists.ibiblio.org>
  • Subject: Re: [NAFEX] Q about metal trellises and why they don't burn plants in the searing summer heat
  • Date: Tue, 07 Dec 2010 20:43:19 -0500

The main problem with the temperature of metal surfaces comes from the fact that much bare metal and some painted metal will absorb to a certain extent in the frequency range of visible light where most of sunlight is, but emits poorly in the infrared where a body of its temperature would mostly emit radiation. Polished aluminum is notable for this. It reflects most of the sunlight that hits it but emits very little heat, so gets hot.

The ratio of total surface area (all of which emits) versus that exposed to the sun (projected area normal to the sun) may be significant, as well as the conductivity of the metal.

My impression has been that Page wire fences don't get very hot.

If you paint your metal white (at least near where it's going to touch the plants), you shouldn't have any problem, as white both reflects and emits well. The tops of passenger airplane fuselages used to be painted white for this reason (maybe still are; I'm not sure). The extra 50 lb. weight on a DC-6 (when the practice was introduced 50-60 years ago) was worth it for the reduced air conditioning load and increased passenger comfort.

Also, normal practice is to enclose the wrapping of your tree trunk or branch in a rubber tube or something similar to avoid cutting into the bark, especially as the plant grows. If you are tying a herbaceous plant like a tomato to wire, just make sure that there is string between the wire and the plant. To be extra safe you could stick a short length of dead twig (probably 1/8 inch diameter would be enough) between plant and wire.

Doug Woodard
St. Catharines, Ontario, Canada


On 06/12/2010 8:23 PM, Patsy King wrote:


Hi everyone,
Hey, I have been wondering for several years: why, when a car or
anything metal is too hot for us to touch in the summer sun, don't
plants that are climbing up metal trellises get burned...or do they? I
suppose things like grapevines that have those hard wire-like tendrils
would not get harm to the tendrils, but what about leaves and stems
leaning against the metal, and what about other types of climbers or
even tomato plants whose stems rest on metal supports surrounding
them? I have some new dwarf apple trees that need support, and I am
planning to erect a strong wire fence alongside of them and grow them in
a somewhat espaliered way. Would the metal burn them?




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