The professional gardeners, who dispense earthy advice to Radio 4 listeners, have been subjected to the threats after suggesting the best way to trap and kill moles, rats and squirrels.
Animal rights activists have become increasingly vocal about the killing and trapping of these animals and gardeners now say they are receiving an increasing number of aggressive emails and letters.
Andrew Tyler, the director of Animal Aid, an animal rights group, said: "The whole premise of gardeners killing squirrels is hateful and bigoted. It's the worst kind of intolerance.
"People should cherish them. But there is a concerted attempt to characterise them as vermin.
His comments come just ten days after nine-month-old twins Lola and Isabella Koupparis were mauled by a fox cub in east London. Following online threats from animal rights activists, a police officer was posted outside the family home to guard the parents.
I think we can judge what is vermin here.