Posted by: Naomi Slade | June 17, 2010

Bad Science

In my eternal search for good, peat free, multipurpose compost, I am somewhat inconstant. I tend to dally with one brand then flirt with another – and then usually return to that Levington one through force of habit.

I am not in favour of using peat, but historically there are several problems with peat free compost. It often does not retain water well and can be hard to re-wet if it dries out. It is frequently coarse in texture making it less good for seedlings and as nutrients may leach out quickly, food resources may be variable. Conversely, peat holds water beautifully but although it is technically a renewable resource, it does depend on how many hundreds or thousands of years you are prepared to wait for your next bag of growing medium.

Being somewhat scientifically minded and possessed of a rare idle moment, I decided to test two composts against each other. I chose different species with different requirements – squash, artichoke and some calendula seeds. I planted some up in New Horizon compost and some in Westland Multipurpose Peat-Free compost. So far so good.

But then I ran into trouble. Although 8 out of 10 cats may prefer something, and 80% is a pretty significant number, if you only ask ten cats then it is not a big enough sample to tell you anything worth knowing (other than that their owners may be victims of advertising). And face cream marketed as ‘scientifically proven to reduce the appearance of wrinkles’ often has in the small print ‘64 of 87 women asked agree…’ (or something). As studies go, that is not a biggie.

Which is where I need to ‘fess up. Science tends to go pear shaped when, for example, 100% of the artichokes in compost A get knocked back by a passing snail. Similarly if all one’s test squashes in compost B mysteriously keel over, it throws the results out a bit. And that is pretty easy to achieve if there is only one of each to start with.

Which left me with calendula. At potting-on time these showed a substantial difference – at 13cm tall in New Horizon compost they were more than 40% larger than the 9cm plants in the coarser Westland compost. But there was only one pot of each and no control compost mixture, so technically not a rigorous test.

And the conclusions? ‘Initial observations indicate that calendula seeds do better in the finer New Horizon compost’ – but I could have predicted that if I had thought about it in advance. And indeed, bigger, stronger plants may care less. I have also reminded myself that science works better when each experiment is replicated many times and properly controlled. But my other conclusion is that, on a domestic basis, life may be too short.

For my next experiment, I predict that 100% of 10 cats are pretty rubbish at gardening… .

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