If you grew these bulbs in pots, just cut back the foliage and store the pots in a cool, dark basement room or frost-free garage. If you grew these plants in the ground, dig them up and store them in plastic bags. Don't tie them up too tightly or they could rot. The idea is to keep them dormant and just slightly moist throughout the winter.
It's definitely worth going to this trouble. Cannas and dahlias, in particular, are expensive to purchase each year. By saving them, you not only save money next spring but these two plants get better and bigger each year. Cannas are easily divided in spring; one canna rhizome can turn into ten within a few years.
Some gardeners take a gamble and leave dahlias and gladiolus in the ground over the winter. If heavily mulched with extra soil and compost, they may survive the winter. I'm doing this with some dahlias I have in my borders. All I can do is cross my fingers and hope the weather is not too severely cold.
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