JaneJudge
I suppose a solution might be that farmers work with universities to recruit people whilst they are away for the summer
Most farmers want workers to start earlier than the end of university. Not only that, but that depends on students' living near the farms or, at the very least, the provision of decent accommodation at a reasonable price. My children have always managed to find easier, better paid work than working in fields, which was vaguely related to their future careers.
Eastern European migrant workers were prepared to work for a few years in countries where they could earn more money than they could at home, before settling down in countries with a lower cost of living.
Some farms in Holland have even been offering sick leave and pension schemes, along with better pay.