The plants on the windowsill just get natural lighting, my largest 'caudata' gets full sun in the afternoons only, as it's on a west-facing windowsill. I don't give it extra humidity, England is fairly humid compared to much of continental US. The plant is in a 5" diameter, dwarf pot (3.5" high) and overhangs the sides by several inches. The pots stands in a shallow water tray, which I fill to 1/2" max in summer and allow to dry out between waterings, watering is greatly reduced, but not stopped in winter, when it is kept just damp, not wet or bone dry. It has formed a loose winter rosette (the same clone kept cooler and drier forms a much tighter, succulent rosette), and the dimensions I gave were from last years carnivorous leaves which have persisted on the plant, these do not persist on plants cooler and drier, it is just recommencing growth now.
This clone frequently splits into several plants, particularly after heavy flowering, so I doubt than it can get much bigger. I don't have a digital camera, but I have just taken a couple of standard photos with a ruler included and I'll try to post the scan on PFT later, this will probably take a couple of weeks.
Last year I traded one of my 'Slack's caudatas' for a plant which was purported to be var. caudata 'Giant', this plant has very similar, but subtly different flowers to my clone, and has so far failed to match it in size or growth rate in the same compost under identical conditions.
My
P. gigantea was even bigger last year, this now has slightly smaller winter leaves and is flowering. I also appears to be splitting into two large plants
.
The use of the loam-based, lime and fertiliser containing compost (John Innes No 2) in my mix is not unusual, A. Slack recommends it in both his books. As I obtained my plant from him, and only had his first book as a cultivation guide, I followed his advice. These plants have always grown well for me over 20 years, so I see no reason to stop using J.I. No2 now.
Cheers
Vic