Thanks for your responses, Iris.

I find the thought of frost to 36" more than a little frightening!
Around here, a bad frost kills things to ground level; less severe
ones just scorch the canopy. We're pretty much at the limit of frost
incidence in NE Oz and probably wouldn't get any at all except for
being on a low tableland.

I recall being in St Paul/Minneapolis in ... April? ... many years
ago, and thought I'd found the perfect climate -- until my host
pointed out there had been about 5 feet of snow in the Uni staff car
park not many weeks earlier. I was chilled just thinking about it!

In article ,
(Iris Cohen) wrote:
can stand frost down to -18 C.

That's 0 in Fahrenheit. Pretty cold. We would consider that USDA Zone 7, so you
are getting conflicting information. Zone 5 means an average minimum winter
temperature of -10 to -20 F, or about -23 to -28 C.

So what the hell do you call "fully hardy"? That means neither the top
nor the roots will die during an average winter in that zone. I think what your
references mean is that the yam is fully hardy in Zone 7, but in Zone 5, the
top will die over the winter, and the roots will survive with a little added
protection. In Temperate zones, it often helps to find out where the frost line
is. Here in Zone 5 in Central NY, the average frost depth is about 36 inches (I
think), but it can vary depending on your soil type.

Cheers, Phred.

--
LID