Phototropism with clear vs translucent light
 

I have a recently acquired C. intermedia in a hanging pot, with roots that look like Gandalf's beard and pseudobulbs that point in every direction. The newest pseudobulbs, however, are growing almost vertical. I am growing this plant in a shade structure with 50% knitted shade cloth, and I suspect that it came from a greenhouse with an translucent covering. I'm curious as to why the new growth is vertical.

My theory is that with non-directional, diffuse light, the new growth can grow in any direction with no reduction in light energy. On the other hand, with an open shade cloth, the light is very directional and growth will tend toward the light. Why vertical and not 33 degrees from vertical (San Diego is at 33N) is another question.

This is more than academic to me since I am deciding on the covering for a planned greenhouse, and I could use a diffuse or clear polycarbonate sheeting, with or without additional shade cloth. Any ideas?

Talk to other growers in your area about what glazing material works best. Even close to the coast your biggest challenge will be keeping it cool inside during summer days.

While it is true that the plants perceive the glazing of the structure to be the source of the Light, I thinks you're attempting to make history fit your limited observation of a new plant.

In my experience, even cattleyas grown directly under artificial lighting can take on a "Willy nilly" appearance in angles of growth.

ES- all the growers that I know have diffused tops. That's why I assumed it was grown that way.

Ray- You are undoubtedly correct. I was struck by the vertical orientation of the two new pb's (only one shows in the photo) and let my mind wander. I have another hanging plant (L. anceps) on a mount, and it has 8 spikes headed South, and one pointing North.

Based on personal experience, I think that between different plants, haphazard growth direction vs. upright habit/direction has a lot to do with plant genetics (inheirited growth habit). Changes within a particular plant are likely due to factors such as whether the plant is turned as it grows relative to the dominant light direction (although this may not describe your situation, a windowsill-grown plant will "lean" toward the window light, but grow more upright when placed under grow lights, or outdoors under a shade cloth).

I think I'll just have to continue to observe the growth pattern on this plant. Here's another comment on phototropism:

Ctt Jewel Box 'Orange' surprise blooms