Good excersises to lose 20 pounds fast?

Well I ride my bike every day for a half hour or longer. I'm outside on the garden pulling weeds everyday, and well I'm just outside a lot. I'm on the heavier side, and my goal for summer is to lose twenty pounds. I eat healthy, but I don't know any good workouts. So far I've only lost about 1.5 pounds.. Which isn't enough. So any help would work.