IF YOU are a regular reader, you will know of my weird fascination with traditional horticultural practices that endure for decades despite being resoundingly debunked by science. In this article, however, I wanted to explore what might turn out to be a surprising bit of irony. Prepare to get meta鈥�
For well over 400 years, was to paint the pruning wounds of tree branches and trunks with various concoctions, in the belief that this would prevent infection and promote healing.
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However, as long ago as , scientists began to ask whether contemporary preparations of white lead, coal tar or ochre actually provided the protection they were believed to. By the 1970s, a series of comprehensive , which investigated more modern treatments such as bitumen, asphalt and synthetic polymers, demonstrated pretty conclusively that these 鈥渨ound dressings鈥� didn鈥檛 prevent decay or speed healing.
The research overturned centuries of dogma. And so, for the past 50 years, the new received wisdom of pretty much every gardening textbook has been that any attempt at treating pruning wounds is and far inferior to simply .
However, here鈥檚 the thorny bit: when you look deep into the studies published since the 1970s, a much more complex picture seems to emerge.
First, it is important to point out that this is an enormously complicated question. The rate and degree at which pruning cuts heal depend on the tree species, the type of injury, the time of year when the wound is made and even the type of tool used. That is before we even get to which compounds are used to treat them.
The 1915 and 1970s studies tested very different substances; today, most mixes on the market tend to be natural tree resins or synthetic fungicides 鈥� very different preparations from those in the 1970s studies, despite these still being cited as proof that the entire practice doesn鈥檛 work.
When we consider more recent studies that investigate the use of fungicide pastes, the idea that all treatments are counterproductive becomes harder to sustain. One 2016 trial found significantly higher wound closure rates on trees like ginkgos treated with fungicide versus a control.
A range of other recent experiments have produced similar findings for other plants, such as and especially . Perhaps because of this, some has started to include caveats to the previously strict 鈥渘o pruning paint鈥� rule, to exclude oak trees.
I wonder if, as further research on new treatments is published, the exceptions will one day prove greater than the rule?
James Wong is a botanist and science writer, with a particular interest in food crops, conservation and the environment. Trained at the Royal Botanic Gardens, Kew, in London, he shares his tiny flat with more than 500 houseplants. You can follow him on X and Instagram @botanygeek
For other projects visit newscientist.com/maker
