Haemanthus Season (What Causes This?)

J.E. Shields jshields@indy.net
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

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