My gladiolas grew to a hight of 6 feet and each corm produced 3 or 4 flower spikes, is this normal?

Do I have to wait ontill the leaves wither to dig them up?

hi ed, welcome to the garden helper. to anwer your question, yes and yes.

healthy glads will send up more than one flower spike, and while i have never had them 6 feet tall, i have had them close to 4.

the reason for letting the leaves die back before digging them up is to give the corm a chance to store all the needed nutrients for next year's blooms. that is how bulbs and corms and rizomes do it.