China seeds, refrigeration times, etc

[Eric Walton]

Dear All

I have been rather quiet of late having been busy digging up 'a few'
treasures from my current garden prior to a move to a larger
property.  Anyway, here are a few of my  thoughts relevant to the
recent discussions....

Due to the generosity of both Roy Herold and Tony Avent, I now
have quite a pots of Chinese Arisaema seedlings.  The seed from Tony
arrived earlier (by about a 2 weeks) but the seedlings are much
more robust for some reason - the trays of pots are side by
side on my deck.  Following Tony's labels the species that are 'slow
to germinate' (?double dormancy) are A. elephas, A. lobatum and what
I suspect might be A. fargesii.  Being late summer/early autumn here,
I am going to allow them go dormant in their own time and go through
a 'natural' winter.  I am optimistic for a number of healthy A.
elephas seedlings next (southern) spring.

Regarding refrigeration times.  I have had a number of Arisaema
tubers form the northern hemisphere at different times.  I try
to get them growing immediately and once they have gone dormant I
give them an artificial winter of three months in a chiller at work
set to 4 C (?40 F) - being a tad impatient!  When brought out of the
chiller I give them some bottom heat (at work!, 25 C) to get them
going.  Usually works a treat and gets things in sinc with the
southern hemisphere.  This year I decided it would be easier to put
the Arisaema in the fridge at home.  'Unfortunately' I had the
opportunity to visit Europe last September and while I was away a
number froze solid.  I guess that was that was because the fridge was
not being opened several times a day.  The bottom line was that the
A. flavum and A. taiwanensis turned to mush when brought into the
warmth, but the A. fargesi (that came from Japan, but I suspect are
actually A. franchetianum) have survived, give or take a few rot
problems.

Someone talked about chilling temperatures.  The scientific dogma
would suggest that (in fruit trees anyway, where I have most
experience) a winter chilling requirement is satisfied optimally by
temperatures around 4 to 6 C.  I suspect Arisaema may have a higher
thermal optima. Subfreezing temperatures are believed to be of no
use.  I have no real idea, but have wondered whether late emerging
Arisaema have relatively high winter chilling requirement or whether
they have a relatively high thermal optima for growth (i.e. need
warmer temperatures).  I suspect the latter.  Any comments?  I
digress!  I suspect one month is insufficient to satisfy a winter
chilling requirement.  Delays in growth resumption are indicative of
this.  The bigger plants may be due to those plants being in warmer
conditions during the initial growth flush.  Though I chill my tubers
for 12 weeks, I suspect 8 to 10 are probably enough, though have
never been game to try it. Getting Arisaema tubers into New Zealand
is hard enough (particularly now) without 'risking them' with short
winters.

On a slightly different tack, I have a few warm (subtropical?) Indian
Arisaema species (A. caudatum, A. neglectum, A. sahyadricum and a
couple of others).  I got the seed in Feb, 94.  Initially these were
a bit of a challenge to grow, not knowing what to give them.  By
chance I found that they seem to come into growth following a
temperature drop.  Consequently, I now winter them in dry potting mix
in the bottom of my pantry.  I pot them up in our spring and put them
on bottom heat (25 C) for about a month (still relatively dry), then
transfer the pots to the floor of the glasshouse and water well.   A
week or two later they come up.  I admit this is all a bit anecdotal,
but it works!  I tried this approach with Wilbert's Amorphophallus
henryi seeds and doubled the germination.  Any comments Wilbert?
So it may relate to other 'recalcitrant' Araceae?

Hope this helps.  Thoughts/comments appreciated.

Eric Walton
New Zealand