NOT a howling success - BUT …

…despair not.  
Recent research tells me I planted the Tubers later than I ought to have, presupposing I'd had already them growing on in the greenhouse for a couple of months but didn't have them to grow on.
With so little yield AND the stem looking to have growing points I though:-
"Nothing ventured,~ ~ ~ ~   "  and reburied it "as is", only deeper.  I'll offer a bit of protection too and see what happens.

"Do not plant Yacon until the soil has warmed and all danger of frost has passed.  The soil must be well drained.  Yacon tubers will rot if they get wet feet.  A perennial in warmer climates, Yacon is not cold tolerant and grows best in USDA Plant Hardiness Zones 5 to 8."


I saw, somewhere, that it's perennial, but in UK it's grown as an annual, hence the deeper burial with probable frost protection.


Best guesstimate - I'm in zone "8"; with the Pennines, and an island of Fells, in "7" and a coastal strip in "9"