Before leaving for a friend’s barbecue the first Sunday in July, Diane Taubner of Concord made her usual stop next door at McGrath Farm to pick up some fresh produce for the party.

But she found the farmstand’s door locked. Patrick McGrath, who devoted his life to farming the land bought by his grandfather, had died unexpectedly of a heart attack on June 30 — a loss that seemed even more poignant as the summer harvest season was swinging into full gear.