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This question is only for light weight plants like lettuce, spinach and spices. I am puzzled by this and I have never tried it, does anybody know any downside in making a diy vertical system with 90° angle other than 45°, I know that for the bigger plants it would be an obvious gravity issue, but lettuce is so light weight that it can usually grow at 90° angle in soil, so I am wondering would this be possible with rock wool and a net cup

The only ones I have seen are angled. The water flows over the roots, the roots usually hang down. The roots cannot go dry when they are exposed in a tube so you need good coverage with the water. I don't know how you would get that with the roots facing the core of the tube instead of the side. if you planted horizontally how are you getting the water to flow around the roots if not down the side of the tube?