The guy I got mine from told me that they really don't grow as well here since they like it hot and the last few years have been too cool for it.

Yellowing might be a sign that it needs nitrogen, how often do you fertilize?

I stuck my Yellow DF cutting in a pot with my American Beauty and Halley's Comet and the other two are doing great so I don't believe it's a fertilizing issue. I typically fertilize it oncer per month with Fish emulsion and liquid kelp at about 1/4 the recommended dilution. I'll try to move it to the sunniest spot I can find and hopefully it will do better.

I think you answered your own question, filtered light=healthy and green, especially in our dry CA enviro. I think S. Meg is more sensitive to extremes than hylocereus, try keeping them in filtered light during the heat of the day, direct morning sun should be no problem. I believe they were growing them out at the USDA field station in the ground until the 'big freeze' of 07? Maybe they had more humidity? BTW, too much shade=etiolation.

good luck,
-Ethan

Are you talking about the DF field over by the former El Toro marine base? They are really cruel there, right now the field is being used to confirm/refute the notion that it's a drought tolerant crop so they have cut off all fluids for it.

My yellow DF has been EXTREMELY slow growing, if it's growing at all, it's the ground, full sun. This photo shows the day of planting (Sep 2010). The thing is STILL the same size, if not a little skinnier. The Physical Grafitti has been sprouting and growing at a decent rate, though not anywhere like the Vietnamese Giants.
{{gwi:1325404}}

The 2 Yellow cuttings I received in Sept. have about doubled their size. For sure, they are not as vigorous as the other DF cuttings. Mine receive morning to early afternoon soon. I apply a weak application of Schultz All-purpose liquid plant feed every few months and/or Osmocote.

I have noticed slower growth as well with the yellow variety. Perhaps the lack of humidity slows down its growth.

Here's something I learned from the vegetable gardening forum, apparently using wood like that can actually rob the soil of nitrogen. Since you fertilize regularly it probably doesn't matter. One thing I would suggest, if you haven't done it already, is to carefully dig down and see if your roots have at least started to set up.

My worst performing cutting has actually been the Vietnamese White Jania, it was heavily corked (they threw it in free) but I think it may be salvigable since it is still deep green.

Here's a question on cuttings. Most of the cuttings I got (all the named ones) were the usual "preserved" ones that had been cut at one or both ends but I also got some newer hybrids that had only numbers (at the time) that were cut fresh from the plant and I allowed the cuts a few days to dry. The freshest 2 cuttings have been growing like champions but they are only growing straight from the undamaged tip (like the vine normally would grow, rather than out from the sides). Is that just because of the freshness?