pushing envelopes - 3 variants

Provenance. This is seemingly little known term, but of
utmost importance in regard to hardiness and micro-climates. It
simply means 'origin' but more important it refers to the exact
location where a plant originated. When you look closely into the
origin and distribution of many perennials including bulbs, it is
often surprising that all of our plants of a single species in
cultivation may come from a single or limited collections from the
wild. Often these collections come from the middle of a species'
range and do not represent the hardiest or most northern (or southern
in Southern hemisphere) population.
Ocassionally a plant is introduced from northern regions of
its distribution and found to exhibit unexpected increased hardiness.

Defoliation/dormancy/evergreen
Jamie, Uli and others mention that some Crinum remain
evergreen or barely loose foliage in winter in their climate. Here
ALL Crinum outdoors loose their foliage every winter*, but all
produce new foliage. The fact that some Crinum loose all foliage and
others just have damaged foliage suggests the range of hardiness or
cold tolerance.
I have heard of some gardeners in mild climates who purposely
cut foliage and stems at the onset of winter to 'push' plants into
moving their metabolism into dormant bud production. Plants that are
allowed to remain evergreen or nearly so, may not develop the deep
dormancy regarded to increased hardiness. By removing the foliage,
the plant goes into full dormancy and increases tolerance to cold.

The relationship between dormancy, degree of herbaceous-ness
and evergreen-ness all indicate a range of hardiness. I suppose one
can envision a plant natural growing in a mild climate, but getting
an early hard frost and defoliating quickly. Later hard frosts have
little effect. Nearby in a more protected area another plant may
just have damaged foliage, but then be more prone to greater damage
later in the cold season because it did not go totally dormant early.
Which leads to....

Ecology
As a totally alternate way of discussing cold hardiness, one
might relate known ecology of a plant to its probable cold tolerance;
i.e. the more we know about how a plant grows in the wild, the better
we might know how it might behave in the garden. (Warning Commercial
Plug!) In my recently published book on the genus Paeonia* (peonies)
I have avoided the use USDA Zones in favor of discussing the native
climate, geography etc. I have rated each species as 'northern',
'temperate' or 'mild', but then given some details about specifics.
We often see a situation where a plant has a very restricted
range today, but in the past had a much larger distribution and this
is reflected by its extended hardiness. A peony example in general
regards tree peony species which are almost totally confined to near
tropic locations in SE China, yet are perfectly happy growing in
northern climates including southern Canada, Scandanavian countries
etc. Not what you'd expect from a sub-tropical species. This suggests
that the current restricted range reflects some conditions other than
cold tolerance - we know they have been dug for medicinal purpose for
millennia and continue to have human pressure on them in nature.

____________
What this all means is that there are many variable to
growing plants that may not seem obviously hardy. Temperature is just
one of a palette of conditions relate to hardiness. Provenance,
cultivation techniques and understanding can overcome some of what
may seem obvious. Nothing is obvious and instead of curtailing
experimentation, should encourage the 'adventurous' gardener to try
again.

Best Jim W.

--
Dr. James W. Waddick
8871 NW Brostrom Rd.
Kansas City Missouri 64152-2711
USA
Ph. 816-746-1949
E-fax 419-781-8594

Zone 5 Record low -23F
Summer 100F +