Cold hardiness of potted plants left outdoors in winter

Mon, 08 Oct 2012 16:44:12 PDT

>The duration of the freeze is irrelevant: one night's freezing solid of a
pot will do the damage.

I probably missed most of the discussion. The reason why bulbs are not very 
hardy in pots is that the bulbs themselves are not very hardy. This may 
sound counterintuitive, but a bulb, being buried in the ground, has no 
adaptive reason to develop hardiness to cold. Most bulbs are not hardy at 
temperatures approaching -10C.
The smaller the volume of soil, the easier it is for cold to penetrate. I've 
killed hundreds of tiny calochortus bulbs this way, until it dawned on me 
what it was I was doing to the poor little bulbs.
There is an excellent discussion of this in The New Plantsman, September 
1994. "Frost hardiness of bulbs".

Bob Nold
Denver, Colorado Z6 

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