Re: frozen plants
Not mentioned except by inference is how plants harden off and the
timing of the process. Although Rhododendron maximum, for example,
when hardened off is hardy to -35F, an early freeze can cause
damage at much higher temperatures. Cornus stolinifera from
northern strains begin this process before southern strains so,
although the same species, the plants differ in their hardiness.
Hence the recommendation to buy locally grown shrubs rather than
those brought in from warmer zones. AS mentioned, if the ground is
frozen any water loss cannot be replenished. So those beautiful
sunny days in March which are so pleasant for us, can be the death
of evergreen shrubs. I think there are two reasons for seeing that
such plants go into winter well watered. One is to provide that
reserve of water, the other is that moist soil will not freeze as
deeply as dry soil. As water freezes, it releases heat which will
slow the penetration of frost. to further protect the soil from
freezing we use a mulch. It takes four times as long for the
temperature wave to penetrate two inches as it does for one inch.
I think the hardiness of perennials is different. Aside from the
frost heaving which we want to prevent, I think too much moisture
in the soil can be detrimental.
Bill Plummer
Painted Post, New York
Zone 5
