How the hell do you think we did it in the past?
Combination of migrants, women and children. Changes in the law in the 1860s, first outlawing children under 8 being land workers followed by compulsory education up to the age of 12, led to a shortage of labour.
The army was drafted in to help but when WW1 broke out they were no longer an option so prisoners of war and the Womens Land Army were used.
The labour shortage continued after the conclusion of WW2 which resulted in the Seasonal Agricultural Workers Scheme being introduced which allowed workers largely from Eastern Europe and the Soviet Union to be brought in.
The use of foreign labour exploded in the 90s as the dominance of a small number of large corporates led to a huge decline in farmers margins which in turn led to a decline in land workers pay.