Friday, December 9, 2016
I've found a Mango (Mangifera indica) only a few years old survived winter temperatures down to -2 Celsius overnight, in hardiness zone 9 in a relatively cold gully in temperate Wellington, New Zealand, Mango is usually classed as zone 10 or 11, subtropical to tropical. I'm confident they would take a few degrees colder given the same conditions.There were however some brown spots on the leaves (visible if you click on image) which may be signs of minor cold damage.
I expect it survived because it got no direct sun until late morning, then dappled sun until early afternoon. It is often the sudden change in temperature when early morning sun hits tender species that kills them. I did not attempt a scientific experiment by planting another one to get early sun, the literature about the risks of planting them outside of the subtropics was so overwhelming, but it now seems it might be worth a try (I did try one in full sun in a very different, somewhat warmer (minimum +2 C) location once, it only lasted a few weeks, but dry soil and coastal gales were probably as much to blame).
I also think it is possible allowing (edible) weeds to grow around it, but not smothering it, protected it from cold somewhat. Planting it out in summer presumably helped as well.
This does not mean it will grow well or produce fruit someday, will have to see about that.
I tried some other subtropicals such as Longan and Inga Bean with more or less the same conditions. They did not survive, although they were very young, most subtropicals get tougher with age, more mature specimens might be worth a try.
Update- October 2017
The Mango did not look nearly as good at the end of the following winter. Most of it's leaves had died, though the plant was still alive and might possibly recover.
The only change I made to growing conditions was cutting back trees that were blocking late morning sun to the plant, it is possible the plant requires near full shade to survive a cool -cold winter. It is also possible it was a harsher winter, some nearby plants that are not usually damaged were this winter. Or perhaps the plant had simply had enough after two winters. Also it did not grow at all over spring-summer-autumn (which is why I cut back the shade trees).