Jon Belber, Holly Hill Farm's director of education, holds up a basil plant to first- and second-graders from the South Shore Charter Public School in Norwell. About 1,200 students went to the Cohasset farm last year to help prepare the soil, plant, and harvest in the "education garden," a fenced area about 120 by 100 feet that at this time of year still teems with herbs, rainbow kale, beans, potatoes, pumpkins, and the occasional tomato.