Thanks for the info Nigel.  I'd never noticed the garden centre (it's La Sinia by the way) although I've driven past it loads of times.  Culti Delta is only about five minutes drive from me on the back road to Amposta.  I didn't realise they were specialists so it's a visit for us this Saturday.
It's taken us 6 years to start getting any success with growing mainly due to the very poor soil and the blasted rabbits but we're starting to get there at last.
Thanks again,
Roger