I live in zone 9B, southern Brazil. We get some frost but only at night a few times a year, and even during those cold snaps, the daytimes can be up to 80 degrees (occasionally staying down low, but it's very irregular). No defined dry or wet season.
When I lived up in NY state we cut back the ferns when they turned yellow, usually when the first frost came. Here, they don't turn yellow.
I started these asparagus from seed, because you can't find them here. I got a few crowns, have them growing in a container type thing to keep it under control. I haven't done a general cutback or a division of the crowns in about a year and I figure it's probably due (they are maybe 3 years old). Should I just go ahead and bite the bullet now that it's chilly? Wait til the cold season passes and risk doing it after spring has sprung? (it's sort of back-and-forth here and hard to tell when spring is actually coming, in recent years especially as weather gets more unpredictable and extreme)
i found a sheet from Hawaii coop extension that suggests not watering them for a month to make them go dormant, but even though we do occasionally have a month-long dry spell, there is no way of knowing when it is going to happen (until it's been a month).
My suggestion is to cut back now. I am in Australia in a similar zone. I am cutting old and green fronds now. My son, who lives inland on the same latitude but has more frosts, has more success than me. He reckons that you can slash (mow) the fronds any time and the crowns will keep sending up spears.