I have never cut back any part of my Amaryllis so far. Why would you want to cut them back? They stay like looking thru the summer months here in Texas. How about pollinating them for seeds?

I cut the leaves back to 8-10" in the fall when I put them in the greenhouse. Easier than storing hundreds of pots with 4-5' leaves. They don't seem to suffer.
Kristi

@kaboehm, which amaryllises do you have that have 4-5' leaves? I'd like to see that!

After the flowering, if you don't need or want seeds, then you can cut the scape. I'm not sure if cutting the entire thing would be the same as just cutting it up at the top where the flowers are. I read that some plants use that green part of scape to still do photosynthesis (makes sense since it is green!).

For going dormant, if you don't intend to dig it up and store it, then it can do that on its own with the cooler temps, though you being in Zone 9, I'm not sure how much cooler you will get to represent the dormant period, but kaboehm is also in Zone 9 and so her steps would be good info.

In my area, I don't move them inside for storage. They stay outside year-round. I normally planted them totally underground but this last winter, I tried a few new ones with the bulb partially exposed. Then we had a late cold front that killed or delayed several of them. I think I will now continue planting them totally underground.

I have nearly 200 different hybrids, so I can't tell you which have the longest leaves....here's a photo from a couple years ago. The shade cloth is at a height of 6 feet.

If you search this forum for "pasture" (what I refer to the summer growing area) you'll see a few more photos.
Kristi

When it's time for them to go into the greenhouse, I cut them so that they leaves are 8-10". They fit much easier on the shelf that way!
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Then, after the leaves have shriveled and dried up, I cut them down to this to open up the neck.
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Give each a quick dusting of Captan (antifungal) powder
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And in the springtime, this is the result; lots of scapes from nice clean necks.

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PS...this is the "old" 6'x6' greenhouse. New one is 9'x9' and much more spacious!