While gladiolus flowers are typically grown from corms purchased from nurseries and greenhouses, these flowers may also be propagated from seeds that are collected from the gladioli that you already have. While gladioli do not breed true -- meaning that flowers grown from seed do not necessarily look like the parent flowers -- you can still get seeds that may be sown the following spring.
Allow the gladiolus flowers to brown and fall off in the autumn, leaving behind the seed pod.
Wait until the gladiolus seed pod is brown and dry to the touch.
Crack open the seed pod to get to the seeds.
Dump the small gladiolus seeds into an envelope.
Seal the envelope and leave it in a cool, dry place where it will not be bothered by rodents or other pests.
Sow the seeds in late winter or early spring in rich soil in full sunlight. The flowers will not appear for the first two or three years.