Answers below are primarily for Stella de Oro, due to not many stats being kept for Happy Returns.
Info to note: All of my CVs were relocated in the fall of 2015 with some making it into their designated beds in the Spring of 2016, and some remaining potted. SDO is planted in sandy soil with mushroom compost, garden soil and alfalfa pellet amendments. HR is potted in a 3 gl. nursery container. Milorganite and Sta-Green 10-10-10 fertilizer being applied up to three times per year, and receiving water every other day via a well water feed irrigation system.
1. Do you grow them in full sun, full shade or part sun/shade?
A. Yes, they receive at least 6+ hrs.
2. Do the plants keep each individual leaf for about the same time as other cultivars that grow well in your garden or do their leaves yellow and dry, individually, somewhat more quickly throughout the growing season? In other words, do their fans look full or do they look more straggly?
A. I would say both produce full fans. The fans stay near full until they begin to go dormant, but do experience some die off of older leaves thru the growing season. Currently, Stella de Ora is completely dormant with all the foliage dying back. I'll have to look at HR to report status.
3. When (if) they flower, how many buds do they have, and 4. Do some of the buds on their scapes never manage to flower (they develop partly and then they dry and drop off, for example)?
A. I am guilty of not tracking stats on a lot of the CVs I have, but if memory serves correct, I would say each scape has around 6-8 buds. I did experience some bud drop but perhaps, a very rough estimate of 70-80% went to maturity.
5. Do some of their scapes start to develop and then they die and dry up?
A. Did not notice any scape loss
6. Do the plants disappear completely underground at any time of the year?
A. Yes, I will attempt to get pictures and update this forum tomorrow.
7. Do the plants stop growing (stop producing new leaves) at any time of the year?
A. This year we experienced an unusually dry Sept-Nov. Even with regular watering I saw a lot of late season inactivity with all of my CV's. We've also experienced unusual temps as of late with the weekend mercury marking in the mid-70s. That and recent rains have many of my CVs sprouting new growth, but believe it is limited to those semi evergreen and some of the Evergreens. Today we are experiencing more seasonal temps for only the second time since fall. Which, may stunt or slow their progress.
8. If they do disappear underground, how long do they stay below ground before they sprout? Or when do they disappear and when do they reappear?
A. I will attempt to keep note of this and try to update.
9. Do their leaves grow normally or very slowly after the plants sprout and appear above ground?
A. Normal to regular growth.
Late Spring photo of SDO
'Stella de Oro'
Edit to add photo of,