Question: What are some things I should avoid in a grow tube?

Answer: 1) Triangular or square shape. The flat surfaces of these shapes rapidly absorb heat when the sun's rays hit them flush at certain times of day. 2) Small diameter & 3) Green color. Small diameter tubes prevent leaves from deploying at optimal angles for sunlight absorption and photosynthesis. Green tubes create an environment rich in green light. Both types of tubes cause the same set of problems. The vine gets the same sensory feedback as if it was surrounded by vegetative competition. In other words, the vine "thinks" it is surrounded by other plants (either physically pressing against it as with small diameter tubes, or reflecting green light as with green tubes).

All plants, grapevines included, respond to vegetative competition the same way: They allocate nearly all of their growth resources to 'primary' growth - growing taller - in order to gather more sunlight and to cast shade on surrounding plants. They allocate almost no resources to 'secondary' growth - stem thickness and root development.

Why bother developing thick stems and strong roots if surrounding plants are going to hog all the sunlight? The result: Tall, thin-stemmed grapevines.