QuestionsHow to growVegetable GrowingRunner Beansvegetables 0 Vote Up Vote Down Tom Leahy asked 14 years ago when to harvest runner beans? 1 Answers 0 Vote Up Vote Down Gerry Daly Staff answered 7 years ago Pick the beans when they are of useable size, and this can be quite small, the size of a French bean and bigger. Home gardeners are not generally trying to maximize yield and picking early extends the season and the quality is excellent.