You won't lose them. You're in a zone where you may be able to grow them all year, depending on your winter. Cannas continually produce new stalks which will bloom even tho old stalks may be exhausted.

Here, we cut the cannas down when a frost kills the foliage, which was just in the last week or two. Do you get frost? I wouldn't cut the foliage until the last possible minute. It will continue to absorb energy for the rhizomes.

Throughout the season, as old stalks finish blooming (each stalk may have two or three flushes of blooms), you can trim down the old stalks so new stalks can take in nutrients and sunlight.

You can cut the stalks to about an inch tall. Don't worry, you're not going to hurt the cannas. In fact, in your zone, they may be "weeds" for you someday. Believe me, if I haven't killed them here in zone 7, with my neglect, they're safe with you. LOL

Hello, I'm in Los Angeles area and cannas are like weeds for me. I totally neglect them...bad soil, not enough water and they still go crazy. Anyway, I cut my cannas back after they flower..but now that I know folks here want seeds... I would just trim off any unsightly leaves and stems. My cannas are going through a rebloom right now. If you get freezing temps where you are at in California, you might to cut back and mulch as other posts here suggest. Susan

OK, I trimmed back the canna's. Did I do it right? What do I need to do now?