hardiness, cold temperatures

John Bryan johnbryan@worldnet.att.net
Mon, 27 Dec 2004 17:03:40 PST
Dear Ken:

Obviously plants that are borderline will succumb to a hard frost. But I
am still of the opinion that going into cold weather dry will give the
plants a better chance to survive. Thicker antifreeze as it were.
Regarding 'bark split' exposed to wind-chill factor will play a part and
such damage would no doubt occur in any case. noticed when warmer
temperatures are experienced and the cells then rupture, dry or not when
the cold was experienced. but only seen when the temperatures rise.  

Your remark that it is 'usually recommended' that plants go into cold
weather wet, in my opinion defies logic, who recommends this? That there
are many factors involved, many not understood is with out a doubt
correct, but I am still of the opinion that dry is better. One is
tempted to ask: If not why not? So much to  learn, so little time!
Cheers, John E. Bryan

Kenneth Hixson wrote:
> Dear members:
>          To quote John Bryan,
> >It is an interesting point you mention regarding plants being dry or wet
> >to survive the colder temperatures.
>          I think the situation is a little more involved than just being wet or
> dry--first, is the damage being caused by actual freezing--ie, are the cells
> of the plant being ruptured by the expansion of the water in the cells of the
> plant?  Plants that have been dry for some time usually survive this problem
> better than plants that are well hydrated, because plants which have been
> dry have their cell sap more concentrated, which acts as "antifreeze".  Also,
> there is less water available to rupture cell walls.
>          If the damage is caused by a cold wind blowing over the leaves of the
> plants while the ground/stems of the plants are frozen and unable to
> transport moisture up to the leaves, a dry plant suffers more damage than
> one which is well hydrated.  This is typical of shrubs which are "burned"
> by a freeze, and while it can kill, often it just looks unsightly and the plant
> will recover.  It is usually recommended that plants be well watered
> prior to freezing weather.  I might also mention that there have been people
> who manually removed all the leaves on a borderline plant, and the plant
> survived the winter when other plants of the same thing nearby which
> were not defoliated, didn't.
>          Sometimes plants-usually shrubs again, are damaged by "barksplit",
> where the bark of a plant will literally split and the cambium layer will
> separate from the rest of the stem, and the plant-usually a shrub or tree,
> will look fine but will later die when the leaves transpire the moisture in the
> plant above the "barksplit".  In my area, Rhododendron davidsonianum is
> notorious for suffering barksplit, often in April, long after the coldest
> weather
> of winter.  In this case, planting on the north or east may make a
> difference.
> Planting facing east is the worst possible location, because the morning
> sun shining on the frost damage will finish splitting what might otherwise
> have slowly recovered.  It is sometimes possible to tape barksplit--simply
> use tape to tightly bind the cambium layer back to the stem, and the plant
> may survive.  I have plants here which have suffered barksplit, and it is still
> visible, but the plant survives.  If the plant is valuable enough, a graft
> from
> below the freeze damage to above the  freeze damage may save the life
> of the plant, if not the appearance.
>          Other plants-in my area, Camellias and Daphne as examples, will
> be top-hardy, but the roots of plants grown in containers will freeze and the
> plant again will look fine but will later die, usually in spring just after
> expanding  the spring flush of growth (leaves).  This is the bane of
> nurserymen, who sell what looks like a healthy plant, which dies soon after
> being sold and planted by a homeowner.  You can imagine what the
> homeowner thinks of that nurseryman.
>          I thought it was 1988 here in Oregon, but perhaps it was 1990, that
> we had a long, mild fall, with virtually no freezing weather, then in early
> November it abruptly dropped to  +18F, and hundreds of rhododendrons died.
> These same plants which were killed at +18F, had only the year before survived
> +5F in December, after a more normal fall pattern.  Obviously, it isn't just
> the absolute temperature, but the condition of the plants themselves, which
> determines the temperatures they can survive.
>          I knew one rhododendron grower who used to claim his plants
> were hardier than plants from other nurseries, because he used a
> Nearing frame (an unheated coldframe) to propagate cuttings.  It is
> true that rooted cuttings from a coldframe/Nearing frame are better
> adapted to the outdoor temperatures than plants from a greenhouse,
> but climate adaptation is not the same as being hardier.  At the end
> of the growing season, his plants were only as hardy as the plant itself,
> regardless of how it had been propagated.
>          To tie this to bulbs, I have found that lilies in containers will
> freeze
> and die--not in December, when it is coldest, but in April, just after the
> current seasons' stem has started growing.  A lily which may have survived
> +5F in December will be killed at temperatures in the upper twenties in
> April.  People from areas where they have snow-cover often suggest that
> keeping the container covered and thus dry, will prevent loss, but my
> experience is that isn't the whole answer.  Keeping them dry may help,
> but perhaps because it also keeps the plants dormant later in spring.
> Covering them may actually make the situation worse if the cover is
> "tight" enough that it is warmer than the surroundings.
>          Daffodils being grown in containers will be killed by temperatures
> much higher than they would survive in the ground, simply because the
> roots are killed.  I'm not sure of the exact cause, just that it happens.
> Jane undoubtedy has more experience than I, but bulbs in containers
> should be in "plunge" material, not just in a covered cold frame or bulb
> frame, to protect the roots.  The "plunge" material is more important
> than the coldframe.
>          Hardiness is a complex subject, and it is easy to misunderstand
> what is actually happening.  Sometimes more than one thing is happening,
> and sorting out what effect did which damage is difficult.
> Ken
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