light

[K Barrett]

I go back and forth as to whether its duration or intensity of light tat makes our plants bloom.. I think the answer is qualified 'yes' but if one was to err I think it would be on intensity rather than duration.. I think plants need a minimum of light but it has to be of a certain intensity. 8 hours of non sufficient light isn't equal to 8 hours of intense light.

Or am I nuts,?

Has anyone any input on intensity vs duration?\

K Barrett

[Ray B]

The quality of flowering is related to the overall health of the plant, but narrowing the discussion as we have done, I suspect that it's a combination of intensity, duration, and temperature that are key.

Photosynthesis is "just" a photochemical reaction, and as such, requires a certain amount of light and a certain temperature to occur optimally. The consumption of the photosynthetically-generated chemical energy (and its storage) are also chemical reactions that are certainly affected by temperature.

Respiration - the consumption reaction - goes on pretty much all the time, but increases with increasing temperature.

Photosynthesis obviously occurs faster with more light, but I believe there is a "temperature inhibition" thrown in there somewhere. Add to that the fact that a plant used to being grown very bright will have less chlorophyll per unit of surface area. All else being adequate, we are balancing a mass of stores creation and utilization - both rate x duration dependent.

So.... longer duration of light at lower levels means a slower generation of energy, and slower respiration and growth. Raise the temperature, and the respiration and growth can outstrip the "building" process of photosynthesis. (There is another reaction that leads to "legginess" in warm, low-light conditions, but let's ignore that one.)

High light level increases the rate of generation, but also warms the plant, increasing the respiration rate. Again, maybe to the point of negative returns, especially if the warming impedes the photosynthesis. The shorter duration means less total mass is created.

However, if we can keep the plant cool while increasing the light intensity without shortening its duration, you "push" the energy creation and storage more than the consumption, so a "stronger" plant should result.

A caveat to that, however, is that some plants don't do well a high light levels. I think I must grow my phals too bright, for example. The best phal blooming I have ever seen was a guy in NJ whose greenhouse was so totally enveloped in algae that you had to wait a minute for your eyes to adjust to the low light levels when coming in from outside.