My first Haemanthus coccineus from seed (after 5 years!) is coming into bloom here also. It has only had an occasional watering over the summer (maybe 1-3 light waterings during each dormancy) and it is still in a greenhouse where the effects of temperature variation likely do not effect it. Also, since they are geophytic with their bulbs below ground it cannot be light sensitivity that leads them to break dormancy.
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
--- On Fri, 8/27/10, J.E. Shields <jshields@indy.net> wrote:
So, my guesses, in order from what I think most likely to least likely triggers for bloom:
1. Relative drops in daily temperatures, from hotter to somewhat less hot.
2. Long term (i.e., annual or even multi-year) entrainment of flowering cycle by climate
3. Day length changes
4. Water