Wait for the bluebonnet flowers to fade and drop from the flower stalk. The bluebonnet produces a bulbous seed pod where the petals once were.
Pick the bluebonnet stem once the seed pod has formed, usually in June. Pick it while there is still green on the plant leaves, otherwise the pod may open and spill the seeds before you can collect them.
Place the stem and seed pod in a bowl and set it in a warm, dry room to finish maturing for one to two weeks. Once ripe, the seed pod cracks open.
Pull open the seed pod and shake out the seeds into the bowl. Pick through them and remove any dried plant bits or pieces of the pod.
Place the bluebonnet seeds into an envelope and label it with the name of the plant and the year the seeds were harvested. Store in a cool, dry place until you are ready to plant the seeds.