Hello Anita,

Your difficulty with disappearing Arisaema sikokianum seems quite
amazing. Myself I have never managed to grow it beyond seedling stage
and have given up on it. The growing conditions you describe sound
perfect, I imagine the soil you prepared this way as a deep rich loose
and humusy soil. Is there nobody out there who has seen this plant in
the wild? Does it not want that kind of soil?
I looked it up in my Arisaema book by Gusman: They describe it as
easily grown but short lived (!) and recommend a raised bed with ample
drainage and a soil of sandy peat accompanied by small rhododendrons.
Otherwise they state the tubers will rot from winter wet. (I do not
know where they garden) That sounds to be the most likely explanation
of your problem.
What also strikes me is the fact that you are very successful with it
in pots. So why don't you grow it on in pots to flowering size?
All of my Arisaemas are potted. A. candidissimum and A. fargesii are
also growing in the open garden. But when it comes to pamper small
offsets to flowering size pot culture is far better than open garden
culture. This experience was confirmed by a friend who runs a small
bulb nursery. Both of us cannot explain this.
There is of course a certain inconvenience in pot culture. But don't
we all do a lot for our treasures?
For substrate in my pots I use my own garden compost from the compost
pile with some general fertilizer added. All my pots are attached to
an automatic watering system in summer so that they never dry out.
Excellent results with A. tortuosum and different forms of A.
consanguineum beside the two mentioned above. They are repotted every
year into fresh compost. The dormant tubers are stored totally dry in
their pots in their compost in my cellar.
I would not bare root them now because you said they have already
broken dormancy, this would cause considerable if not fatal root
disturbance.

Hope that helps

Uli