I think every plant I've ever lifted other than the tap roots like carrots, dandelions etc have had a rootball considerably wider than it is deep. Vertical gutterings with a dandelion in the top of each one would certainly be unusual.
Doncaster, South Yorkshire. Soil type: sandy, well-drained
Thanks for the replies.Basically,I was looking for a cheaper and lighter alternative to sleepers(I was going to glue wood over the downpipes and then stain and varnish it).I can still do that if I lay the downpipes horizontally(which was my original idea),but in a moment of insanity I thought if I stood them vertically I could plant something inside them.Ah well,I know better now-back to my original idea!
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I don't understand how you could use them horizontally other than that way.
I live in west central Scotland - not where that photo is...
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.