I spent much of last weekend discussing the re-sexing of trees. Not your everyday Sunday papers conversation – but fascinating none the less. How come?
Well, I had staying as house guests Tom Ogren, world authority on allergen-free gardening, and Nigel Clarke, garden-centre owner extraordinare who aims to turn Guernsey into the first ever allergen-free island! They were touring the UK, watching birds (of the feathered variety), visiting horticultural centres and speaking at arboreal conferences – and stopped off in Lawn Road to checkout the progress of our apple tree, planted on Tom’s instructions after his last visit, and to discuss the re-sexing of trees….
As anyone who has looked at the low-allergen gardening pages of the FoodsMatter site will know, Tom has written widely on low-allergen gardening and how to make both our personal garden spaces and our communal civic spaces less of a hazard for the 2o% plus of the population whose lives are made a misery every year by pollens and moulds.
Tom’s researches over the last 20 years put the blame for the dramatic increase in inhaled allergies firmly on males – male trees, that is. Eager to regenerate themselves, male trees puff enormous quantities of pollen into the atmosphere each year in the hopes that the winds will carry it far and wide and fertilise many female trees on the way. This is a perfectly reasonable thing for them to do and, from a town planner’s perspective, pollen is light and makes very little mess. Female trees, on the other hand, suck pollen out of the atmosphere but then produce fruits and nuts most of which, in due course, fall to the ground creating a horrible mess for city authorities to clear up. So, city authorities plant male trees thus adding every year to the total pollen load in the atmosphere.
Back in our gardens, we are totally unaware of the sex of most of our trees and plants – as indeed are most of the people who sell them to us. So, if it looks pretty, as do, for example, highly allergenic birch trees – we just buy them and plant them. For all of us, gardeners and garden professionals, Tom has devised a plant allergen scale called OPALS which rates plants and trees according to their allergenicity, 1 having the lowest allergen potential, 10 having the highest. Nigel, who is doing all kinds of revolutionary things in his garden centre in Guernsey (see this article on the FM site) has now had special plant labels made which include the OPALS rating so that you can easily pick out the plant which will be least likely to make you suffer.
Together with other garden experts they have now set up a charity, SAFE Gardening (Society for Allergy Friendly Environmental Gardening) to disseminate their ideas, improve public awareness and, hopefully change both public and private gardening practice. An ambitious aim, but every great idea has to start somewhere. And, as more and more people are made ill by inhaled allergens, medical research and health policy makers must surely start to look for ways to prevent the epidemic rather then merely to medicate it.
(If you want to see just how pollen floats off trees into the air, look at the short video on the SAFE site.)
Ah yes, I hear you cry – but what about this re-sexing of trees?
Well, Tom’s solution to the pollen crisis is to replace male trees with female trees but, to do the job properly, this would involve cutting down all the male trees and planting female trees in their place. Not only would this be horrendously expensive but it would devastate the landscape for 20 to 40 years while the new female trees grew to a reasonable height. So, understandably, the chances of it happening on any significant scale are pretty minute. But, what if you could actually change a male tree into a female tree?
Among his many other horticultural skills, Tom is an expert grafter and he is now looking into the possibility of grafting female trees into what would effectively be a male rootstock. I am hoping that he is going to write about this for us in some detail when he finally gets back to California but the theory is that you would pollard the male trees – a quite common practice in many urban areas – and then graft female tree stock into the branch above where the next shoot would come. (I think I have got that right….) The result would be a male trunk and major branches, hosting female lesser branches which would suck up pollen and bear fruit instead of spewing pollen out into our air! What a riveting idea….
Meanwhile, if you want to know more about low allergen gardening, check in to Tom’s site, Allergy-Free Gardening, and keep an eye on our fortnightly e-newsletter where we will be flagging up Tom’s articles on re-sexing trees and pollution-bearing pollen (another fascinating area) and Nigel’s on his plant labels and his plans for an allergen-free Guernsey!
I am looking for a way to keep Sweetgum trees from producing the fruit. I have been told about spray that if you use during a 7 to 10 day window in the Spring it will fool the female tree into believing they are Male or visa versa. The weather has to be perfect and cannot have any rain for a couple of days. This only works for a few years before the tree catches on to the trick and is very expensive.
I have also been told there is a treatment that if the roots of the tree are treated will permanently change the Sex of the tree. That it is Expensive and no gurantee. Don’t know any more than this.
What is your experience
Hi Dave – can’t help I’m afraid but I’ll pass your query on to Tom and Nigel.
Dave, Michelle,
A better choice than a regular sweetgum tree would be: Liquidambar styraciflua ‘Rotundiloba’, also known as fruitless sweet gun tree. These are always sold only as grafted trees. I;ve seen them, and they’re very nice,….the leaves have a more rounded shape, but they form none of those annoying sharp seed balls.
But for an existing tree….if it were pollarded each year (just as they often do with London Plane trees) this will get rid of both the seed balls and the pollen from male flowers.
Spraying with Florel will also get rid of these…the flowers need to be sprayed just before they would open (before the male flowers start to shed all that bright yellow pollen.