Ron made a good point, check with other collectors that are up in more colder climates to see what they have experienced from the past winters.
For us living this far south, we know what varieties are cold sensitive for even us. Some of them for me would include, Green and Gold, Bogoriensis, Nestor, Dreadlocks, Lt. Paget and I'm sure a few others. But remember, these are well stablished plants in the ground growing, not container grown plants, that list would be much longer.
Cold tolerance/resistance is another one of those topics we could go on until springtime.
Jeff - From those on your list, the only one that I'd consider sensitive is Green & Gold; the others have held up fairly well both this winter and last. A Dreadlocks in the ground for 6 mos got toasted by too much sun earlier and looks even worse now; in another part of the yard, a 3 gal Dreadlocks sitting in its pot looks almost as good as the day I bought it about 3 mos. ago. I've got a few plants in which one part looks like crap and the other part is fine; one branch is wilting and the one next to it is fine. Our collective annecdotal lists are probably rather extensve with lots of apparently contradictory evidence, but some winners and losers should emerge.
I'm more convinced than ever that what we are calling cold tolerance is a function of the following: air temperature, air humidity, air velocity, and time (duration of cold event).
Air temperature: kind of obvious but why do some plants suffer at 50F and others can take 30F?
Air humidity: think dewpoint and frost
Air velocity: although plants do not experience wind chill the way mammals do, we all know from experience the good and the bad wind can do (warms the air over water to shredding leaves)
Duration or time: the longer the cold event, the greater the probability of damage.
Since I'm on a roll, a few more thoughts from a deranged mind: What is going on in the croton leaf when it starts to wilt up to the point where the water in cells freezes and upon thawing gives us mush? or why do some leaves lose their water content easier than others? (thereby wilting). How is this amplified by wind velocity and low humidty?
How much water can a leaf loose before it is beyond recovery? (We've all seen wilted plants recover after good watering, but we've also seen those that never recover - especially in winter) How does air or soil temperature affect this ability to recover?
...or are you suggesting I go get a doctorate in plant physiology??
Has anyone ever tried Wiltpruf (or any of those concoctions to keep your Christmas tree from dropping its needles so quickly) ?
Jeff - Are there any products out there that a nurseryman might use to reduce wilting on plant leaves? something to reduce trasnpiration through the leaves?
A bit off topic, but since most of us also grow palms, why are some very cold tolerant and Cyrtostachus or a Pelly will start a death dance at 50F? Something a bit more definitive than 60 million years of evolution...
But there are lots of palm species in the world but only one Codieaum species so why so much variation in one species even if it is genetically unstable?
Anyone looking for a subject for your doctoral dissertation?
I have leaf drop on plants that did just fine last year. I think it is because we started with the extreme cold so early in December. It is only the 9th of January and we have many more weeks to go. Normally our " trim" date is always the first weekend of March . It is when we start to see things waking up and starting to grow . That is 8 weeks from now. That is a long time to stress out these plants , or any other tropical plants for that matter. I hope this doesn't continue to happen. It’s a real bummer .
I have at least 100 different varieties in the ground, some as long as 13 years, and I can tell you honestly, what was cold tolerant one year, dropped leaves like a bad habit the following one or two years later or three years later. No way to predict. Yellow Excurrens, one of the toughest, went through last winter as bare as an empty hat rack. This year, they're thriving. Dreadlocks drops leaves completely if you walk past it with a cold beer and yet this winter, it's full of beautiful new growth. King of Siam, on the north side of the garden and unprotected, has never shown cold damage. Norma is the same. Thanksgiving, right next to both of them and in the ground twice as long (9 years) sheds leaves every winter.
There's no science to any of this. Your Crotons are, as mentioned, all the exact same species in the exact same local environment. It's all a matter of micro climates, cloudy days, and whether or not some passing raccoon took leak on the main trunk of the Gloriosa or the Thea just before it turned cold. Remember, Codiaeum variegatum is in reality a small tree that's deciduous north of zone 11 in both cold and drought. Gee, doesn't that sound like a Florida winter?