Tropical bonsai

[coh]

In my experience, tropical trees can adjust to cooler temperatures. The only thing they absolutely cannot adjust is freezing. By genetics, the concentration of solutes in the fluid of their cells does not lower the freezing point much at all so freezing easily occurs and burst their cells. This kind of adjustment takes evolution over many many years. We don't live long enough to see that happen.

It's an interesting issue. I was browsing through some books and videos by Jerry Mieslik the other day. For those who don't know, he grew large ficus bonsai in Montana, mostly or completely indoors under high intensity lighting. He claims that even if your ficus doesn't show immediate damage from exposure to cold temps (and here I'm referring to above freezing but "cold for ficus", maybe upper 30s to mid 40s), the plant can suffer in the long term from that cold with reduced growth in the next season. OTOH, I got my 2 large ficus microcarpa from a grower in our area (Hollow Creek Bonsai for those who might be familiar, but he has since shut down his operation) and he said he left them out pretty late and they were exposed to frosts and maybe even light freezes without evidence of significant damage.

So I have compromised - smaller ficus and those which I believe to be less cold tolerant (willow leaf for example) get protected or brought in for the night when temps start dropping into the 40s while the large and difficult to move microcarpas stay out until temps get below 40. I won't chance frost or freezing any of them though there have been a few nights where it got colder than expected and it got close. Does that cold hinder growth in the long term...not sure.