A couple of summers ago I was looking at an infestation of Corn Marigold in an arable crop in Pembrokeshire. I foolishly (what’s new?) asked the farmer where the plant usually grew and he said “there’s a bit of a clue in the name – Corn Marigold” – drrrr….
And there’s a bit of a clue about my attitude towards magical thinking in the sub-header to the Potwell Inn title. “A sceptic’s take on being human” . Whilst I will happily assist at the Wassail, say a prayer and bang a saucepan, I don’t go home afterwards puffed up with pride that, once again, I’ve driven off the evil spirits. If only it were that easy. In fact if I had a pixie dust tree on the allotment I’d be a wealthy man with a lot more followers than I’ve got just now. On the other hand, last year’s Snake Oil Extract is going well at £50 a shot when you buy it over the bar.
That just about sums up my attitude to whacky gardening theories and unsubstantiated golden rules. There’s usually a crypto religious hierarchy somewhere, selling off the secret knowledge and running seminars at eye-watering prices. 
Scepticism isn’t the same thing as cynicism which presumes something’s bad before even examining it. True scepticism is always open to the possibility of an idea going either way – it just demands the opportunity to give it some thought, read it up perhaps and even try a couple of experiments.
So when I saw a mention of ‘moon gardening’ – in Mark Diacono’s “The New Kitchen Garden” (on page 247 if you happen to have a copy), in a section about the management of the garden at Tresillian House in Cornwall – I had to think a bit. First point, moon gardening is not quite the same as biodynamic gardening. They’re related but separate disciplines. Moon gardening seems to pay attention to phases of the moon for different operations in the garden. A quick check online suggests that there’s a more complex formulation that includes the pasage of the moon through various constellations but that part has a high cringe-factor for me in much the same way as the full Steiner method does. There’s a bit too much esoteric that in the end boils down to “because I say so!”
The point that I found most interesting was the notion that the passage and phases of the moon not only affects the tides but also groundwater. Now that’s a big claim, but at least it’s potentially testable, bearing in mind the huge number of variables at play – surface evaporation, recent rainfall and so forth. And there has even been some serious research into the behaviour of aquifers close to the sea, that shows a mild correlation. Living close to the sea, and especially if you’re close to the huge tidal range of the River Severn, for instance, it wouldn’t be inconceivable that the rate of run-off could be affected by the spring and neap tides. All you need to do is look at the rising and falling of the water level in the rhynes (drainage channels). The question then is – how far away from the river/sea, and how high above sea level would the effect still be noticeable?
You’ll never put weight on eating your words!
So back to the allotment because theories don’t grow cabbages. Our allotment is maybe ten feet above river level when the flow is low. When it floods we’re a lot closer. According to my OS map we’re 25 metres above sea level, so if there’s any validity in the theory we’d possibly experience some benefit. If we conducted a trial, the one certainty is that it could do no harm, but I’m sure that trial results can be skewed by confirmation bias. The other source of error would be that anything that increases particular attention on the allotment is bound to bear fruit in some way – the farmer’s boot is the best fertilizer.
Charles Dowding (the no-dig man) makes a positive case for the moon in his book “Organic Gardening the no-dig way” – Pages 67-69, and does it in an open and non-sectarian way. The tricky part is demonstrated by the old tradition of planting potatoes on Good Friday. The date of Good Friday and Easter is the only major festival determined by the moon and consequently it can vary by some weeks – at a time when the last frost date is a crucial marker for planting times. So should you follow the moon or the frost dates? I know which I’d go for!
On the other hand Ken Thompson in “The Sceptical Gardener” – Pages 100 – 103, not only rejects the idea he digs it up, flame guns it and gives it a good spray of Roundup to make sure, and with more than a touch of religious fervour. In fact he gets so cross about the “relative positions of objects hundreds of light years away” that he appears to forget that the moon is very large, very heavy and very close. The fact that it’s burdened with a huge symbolic load is not a scientific argument.
So is it worth a try? I reckon it’s an extremely long shot but anything that increases our sense of embeddedness in the natural order is bound to be a good thing even if it doesn’t grow longer parsnips.
A fellow gardener I knew years ago swore by moon tilling to kill weeds…she’d go out at dusk during the full moon to do her tilling and the weeds didn’t come back. Just to show me, she tilled the next section during the day (when my view was that the heat of the sun would kill the tilled weeds more quickly and thus be more effective) when the moon was no longer full. Within a couple of weeks, that section was filled with weeds again. I was still a doubting Thomas, but she repeated the experiment over and over and the moon tilled ground always remained cleaner, even if she switched sides of the sections…..I no longer till, but if I were preparing a new garden site, I think I know when I would work the ground!
The trouble is, there’s a lot of money to be made by undermining traditional disciplines so you can sell more chemicals. I think your friend has it exactly right – if a technique works consistently for you then it’s probably worth pursuing. How many traditional herbal remedies have been the source of important drug treatments? Science needs to try not to be so imperialistic in its claims.