In article , Paul Bonner
writes
My potatoes are now 3ft 6 in high.
They are strong, lush and dark green. I am worried that they are going to
turn out all top and no tubers.
What fertiliser should I use to encourage Tubers and less green.?
The ground that they are on has had several bonfires on it and there for is
rich in ash

Help please and thanks.

3ft.6in. high already! How many times have you earthed them up - i.e.
ridged them ? Each time they are earthed up, they develop a new group of
tubers just below the top of the ridge and the energy of the plant goes
into developing those rather than into stems and leaves etc.
--
Alan & Joan Gould - North Lincs.