Gladiolus tipping
by Chris
(Fairport NY)
Doug says it sounds as if you didn't plant them deeply enough so the roots could get a good hold on the soil.
That said - this can happen in sandier soils and in high-wind conditions. Many folks stake them for that reason. I never did when I grew them commercially for cut flowers but we did make sure to plant them deeply and then hill them up during the growing season to keep the tips straight.