In case you hadn't noticed, our region is a bit different than most of California. For one thing we have this thing called "winter" to deal with. Although we may not get as much precipitation as we would like during the winter, we still have to deal with the effects of prolonged exposure to cold. In this way we are more like Missouri than California.
Recently I was asked about overwintering dahlias and gladiolus from the community garden. These are 2 plants that should not be left in the ground through the winter. In the case of gladiolus, in some winters many cultivars will survive but why risk losing your corms? (Corms are what gladiolus "bulbs" are really called.)
I was going to write a detailed post on overwintering glads and dahlias, but since I'm lazy, I checked to see if there wasn't something out there already written that would work. Fortunately Purdue's Cooperative Extension has a good fact sheet on keeping begonias, dahlias, geraniums, cannas and gladiolus through the winter.
Rather than reinvent the wheel, I'll just point you to this good resource. ⇒ https://www.hort.purdue.edu/ext/HO-085.pdf It mentions fungicides in the fact sheet. If you're in California, you should ignore those parts.