Haemanthus Season (What Causes This?)
J.E. Shields (Fri, 27 Aug 2010 10:23:26 PDT)

Aaron and all,

My bulbs are stored in a small home greenhouse over summer. The inside
temperatures range from 30 F above outdoor temperatures in late afternoon,
even with the exhaust fan running, to ca. ambient by morning, so the plants
definitely experience a temperature shift even on a daily basis. They also
experience a reflection of the ambient temperatures when those
change. Changes in relative average temperature could still play a role in
signalling the initiation in flowering, even though I agree that absolute
temperatures do seem to be irrelevant.

My bulbs all grow with at least their necks at the surface of the pots, so
there is opportunity for them to perceive and react to changing daylight
hours. My impression is that they grow with their bulbs partially
exposed in nature as well, but I have not actually seen many of them in
the wild.

A point in favor of long-term programming of the growth cycles is the
difficulty that mature bulbs have in adapting to the change of season when
moving from the Southern Hemisphere to the Northern. This suggests to me a
very strong long-term programming.

And of course nothing seems to preclude there being multiple factors that
affect bloom and growth cycles in Haemanthus. A professional plant
scientist with access to controlled growth chambers could probably sort
this out in just a couple or three years.

I don't see a causative role for water in the regulation of the flowering
cycle in Haemanthus. This is, however, not to say that water does not
affect the growth cycle.

Jim Shields

At 09:49 AM 8/27/2010 -0700, you wrote:

.....
I would say it is programmed into the bulbs -- their is likely a
chemical buildup during growth period or when going into dormancy that
slowly breaks down on a schedule over the dormant period. Once this
growth inhibitor is depleted they germinate. Cool temperatures are likely
not the factor as mine had cool summers and cool nights (55-60F) the
first three years in Tennessee, but this summer was warm and had warm
nights (75-80). The latter was similar to the temps in Kansas where they
began life. In all cases growth has begun the last week of August to
first week of September.

What I would be curious to know is if dormancy (leaflessness) is reached
at the same time by those whose plants are growing now.

Aaron Floden
Knoxville, TN

*************************************************
Jim Shields USDA Zone 5 Shields Gardens, Ltd.
P.O. Box 92 WWW: http://www.shieldsgardens.com/
Westfield, Indiana 46074, USA
Tel. ++1-317-867-3344 or toll-free 1-866-449-3344 in USA