"Martin" wrote

You can grow carrots in vertical plastic drain pipes (as seen in a
programme
about people growing giant vegetables).

Wouldn't you need hundreds or drainpipes?

How many 5 metre long carrots were you thinking of growing? )

Oh, I misunderstood. I thought you meant growing just normal everyday
carrots in them! I imagined growing my Early Nantes in drainpipes but
thought that would be going over the top!!