Maybe it is to do with the fact that we are dealing with living things, always with that element of unpredictability. Driving, or doing DIY projects are simple exercises in cause-and-effect by comparison; natural systems are so much more complex; the results of our interventions often not obvious.
My thinking about this was stimulated by a recent double page spread in The Observer newspaper last Sunday - Nine Garden Myths Debunked. It was the science pages, and flagged up a website I had not heard of before - Garden Professors - hosted by Washington State University's extension service. One of the people behind this is the university's Dr Linda Chalker-Scott, who I had come across before when I discovered her books in the Royal Horticultural Society library in London - readable little guides to what works and what doesn't in the garden. Valuable stuff, especially for those new to gardening, who find it difficult to face down an older and more experienced gardener telling them, in no uncertain fashion that "you must do it this way". Maybe that is the problem - too much learning informally, too much folk-knowledge passed down from unquestioning generation to unquestioning generation. Sometimes circulated by garden writers too.
Actually, the Observer piece set up a bit of an aunt Sally here by including some of the prescriptions of biodynamic gardening/farming (here listed as myth number six), which are so self-evidently dotty that few people this side of cloud-cuckoo land believe them. Bit of an easy target that. The first myth debunked, that of compost tea, did make me think about the sources of myth though. This particular myth is, I think, a relatively modern one, the result of pseudo-science emanating from the organic movement, who have been particularly prone to generating new myths. Number two - Lighten clay by adding sand, is, I think, actually more interesting as myth, as it has been around an awful long time (Victorian days?) and is devoid of any of the 'muck and magic' ideological overtones of the organic movement. The truth about myths no. three and eight - Young trees should be staked and Add bonemeal and compost when planting trees, have been known 'in the profession' a long time, but has not got out into the amateur world sufficiently. Given how hard it is to buy decent tree stakes, this is jolly good news. Sun through water burns leaves is another Victorian one I suspect, as are Tree wounds need dressing and Gravel helps containers to drain. Myth nine - Natural is safer is a rejoinder to the organic movement.
Nine is just a start - there are many more out there.
Interesting that a national newspaper decided to devote its two page science section to the subject of gardening myths. Shows how important we are perhaps, or maybe how prone to delusion. I can't help feeling that as old myths die, new ones take their place. There is an awful lot of belief involved in gardening, or to be more precise there are belief systems which people cling to, sometimes with an almost evangelical fervour. The organic movement in particular has had its fair share of 'true believers'. Permaculture too - why do people get so fanatical about it. Is this gardening as religion?
One of the problems with gardening myths is that few of us really make good scientists (I include myself here). A lot of us 'experiment', by which we mean try something different and see if it works. But setting up a trial with a proper control and being really disciplined about it takes time and very often space. We are far more likely to try something one year, and something else the next, and then draw the conclusion that whatever worked best, must be best, although a thousand and one variables would have affected the results. If we do do a full trial, making sense of the results is often far more complicated than we imagine possible when we set out - science often does not give clear results.
One source of myth is, I suspect, is the gardener who always does something a particular way, and being a good all-round gardener, the results are good, so they make the mistake of assuming that because they have always done it that way then there is a relationship between a particular course of action and the results. In fact the course of action may be neutral, irrelevant or even harmful, but its effects outweighed by other beneficial courses of action. I once met someone who grew orchids in pots with the bottoms of the pots permanently immersed in water, and which she promoted as 'the way to grow orchids' - which any orchid grower would describe as madness, as these are plants which need impeccable drainage. She must have been doing a few other things right, as her plants seemed happy enough though.
I suspect that as old myths die, new ones come to take their place. Today, I suspect we have an unholy alliance between marketing boosters and journalists on the one hand and the commercially minded wing of the organic movement on the other. I am also old enough (55) to see myths develop. Just to take one example, the extraordinary growth of the idea of raised beds for growing vegetables. I think it was Lawrence D. Hills who started this - he was a pioneer of the 'rational' wing of the organic movement in the 1950s and 1960s (as opposed to either the 'magical' biodynamic crowd or the bunch of mystics and fascists involved in setting up the post-war Soil Association). Hills had various ideas about why raised beds are a good idea, chief of which was the idea of avoiding soil compaction (you don't walk on your raised beds).
Raised beds can be a good idea for various reasons. In particular, those of us who are getting a bit creaky find it much easier to tend veg plants at a little above ground level (we have three, about 15% of our veg plot). But there are so many disadvantages: they heat up and cool down more quickly than the ground does, they are singularly inconvenient for root veg, they need considerable work in constructing - like finding all that soil to fill them with. Yet so many gardeners feel that they have to grow their veg in them. They are a manufacturers and salesman's dream - all that wood (and preservative) or plastic or whatever. No wonder the mail-order catalogues and the garden centres are full of 'raised bed kits'. The wooden ones (i.e. most of them) only last x amount of time before they rot and collapse. The worst, from the sustainability point of view, are railway sleeper beds - all that wood, what a waste! The hold over novice gardeners that they have to grow their veg in raised beds has become quite extraordinary. Another myth to combat!