The rains came early.
I did it.
86% humidity in the air. 15°c at night, 23° daytime. Torrential rain planned for the next two days.
I decided this was my window.
I considered @roseseek 's advice to bareroot. But I was afraid a newbie like me would screw up the bare rooting process and break too many roots.
I decided I was going to only repot Heritage and leave Teasing Georgia in the current trough. I figured that this way, I might kill only one of them and would disturb the roots of the other as little as possible.
I used a spade to cut straight down through the soil, roughly down the middle of the pot between the two roses. I heard the terrifying crunch of roots breaking.
I pulled Heritage out. I was relieved when the soil on her side of the pot came out in one piece, a large moist cube that held its shape around the rootball. I could only see roots on the side I had cut with the spade.
I immediately plonked the whole thing down into a prepared 21 liter (5.5 gallon) pot.
Then I backfilled both her pot and the gaping hole in Teasing Georgia's pot.
I took @Sheila z8a Rogue Valley OR 's advice and didn't prune. I saw a video from Fraser Valley rose farm where he advises against it, saying not to compound injury to the roots and the upper parts of the plant, and it made sense to me.
Two days later: Heritage is looking perkier than ever. There has been some leaf drop, but all of those that fell off so far have been leaves that were scorched by the sun this summer. More excitingly, I am seeing several buds growing!
I think she will be ok. There is more rain scheduled for this afternoon.
Teasing Georgia has dropped a couple of leaves too but otherwise seems to have been totally unbothered by the process. I will repot her eventually, but not until January.
Thank you both for your advice, I didn't follow everything but I did wait for the rain thanks to you!
Q
Good question !
Q