Fanged Parsnips: thinking about evidence

I’ve been having a conversation on Twitter with John Harrison (@allotmentorguk) about the truth or otherwise about manure causing forked parsnips. He posted advice a couple of days ago reminding gardeners that carrots & parsnips don’t like soil that has been manured the previously autumn as it causes the roots to fork & split. I disagreed with him, at least about parsnips, as I had a vague memory of reading somewhere that research had indicated that this wasnt actually true. John tweeted back that he’d be interested in the link, but could I find it? Nothing! I’d lost the information & felt a bit silly.

However, I’ve been sleuthing & have come up with some interesting results. Firstly, its evident that information gets repeated without much checking back as to its veracity. Every search I did came up with a list of sources, each merely repeating the ‘fact’ of manure causing forked parsnips, but no evidence.  I know from our allotment that carrots do fork in manured soil, but our parsnips tend to fork if sown in stony soil – & our chalky soil is full of flinty stones. I also remembered the origin of my questioning of the link between manured soil & forked parsnips; it was Joy Larkcom, in her book,  ‘Grow your own Vegetables’, who said: There was a long-held belief that growing on recently manured ground led to fanged roots, but experiments have demonstrated that this is not necessarily true (Larkcom, 2002; 298). Unfortunately, she gives no further information. Continue reading