Cut off the flower stalk 1 to 2 inches beneath the bottom-most spent flower with a pair of shears once the flowers begin to wilt and seed pods begin forming. Seed pods resemble brown or tan spheres with a papery covering.
Place the hollyhock stalk in a paper bag. Cut the stalk in half or thirds if it is too long for the bag, then place the cut stalks in the bag. Set it in a warm, dry room for one to two weeks or until the seed pods begin to split open. The bag catches any seeds that spill from the pods as they dry.
Hold each seed pod over a bowl and finish splitting it open with your fingers. Shake the seeds from the pods and into the bowl.
Remove any plant debris and non-seed material from the bowl. Shake the bowl lightly and the heavier seeds go to the bottom with the plant debris raising to the top, making removal easier.
Label an envelope or jar with the type and color of hollyhock and the year harvested. Place the seeds inside and store in a cool, dry place until you are ready to plant.