Janet Oldroyd Hulme, co-owner of the area's largest grower E Oldroyd & Sons, said: "Lectures and tours have been selling out since before Christmas. The interest helps sales enormously."
As for this season's crop, she said: "The warm weather in the autumn helped us by keeping the roots active, but since then it has delayed our start because they need frost to enter dormancy.
"Growers who haven't insulated their sheds may struggle to catch up. For us, the early crop is down slightly, so the others are likely to be too." The festival runs on 24-26 February.