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I'm considering trying to improve my indoor herb growing. It seems that under certain conditions, one could easily run strings of LED lights at the soil surface, which would allow for the plants to grow tall without the complexity of an overhead support structure. Plus, I think it would look pretty cool.

My question is: can you grow small plants with the lighting coming from below the leaves? (assuming that the lighting is bright enough within the bands that chlorophyll will absorb). I would think this would affect the plant's growth pattern; has anyone here tried this, or found records of those who have?

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    Not an answer but a thought, as long as the light source was greater above than below. It may add something to the lower leafs. – Dean Hagan Mar 8 '18 at 0:02
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    Not an answer, but it seems like when tomato plants are root-stressed and can't handle the strong sun, they sometimes turn their leaves upside down (I suppose in an effort to get less light). That's just an idea based on observation, and such, though. It's possible that some species of plants may be different with regard to the bottom part of their leaf function. – Brōtsyorfuzthrāx Mar 10 '18 at 22:08
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Lighting a plant from beneath will cause the plant to grow towards the light, ergo, downwards, if it grows at all. Phototropism is the name of the process induced by lighting or sunlight from above - the plant wants to maximise the amount of light it receives, and therefore grows up towards the light. If you place the light to one side, the plant will virtually grow sideways; you can see this in the wild or even in a garden, where plants are perhaps covered by a dense canopy above, or planted much too close to a fence, and therefore produce growth that is reaching forward, almost sideways, groping towards the brightest area. I'm afraid your suggestion simply won't work in terms of growth, but if you want to use small leds at the base of plants for purely decorative reasons for short periods, that should be fine.

UPDATE IN RESPONSE TO COMMENTS:

I'm not going to reproduce a full botanical lecture here, but will add a little more info. Light is one of the most important things controlling plant growth; plants have a set of photo receptor proteins, four of which have been identified so far. Photosensors in particular detect the presence, strength, colour and direction of a light source, and that information is used to dictate direction of growth (phototropism), which is the most relevant for the question asked. There's also proteins called phototropins which are activated by the presence of uv/blue light wavelengths, and these too are involved in directional growth, although they're also involved in directing chloroplasts in order to maximise photosynthesis, plus one or two other twiddly bits. It's quite a complicated, synergistic picture, but simply put, your plants ain't gonna grow well without the proper wavelengths of light placed at an optimum distance above your plants. Simply put, you could view leaves as solar panels, angling their upper surfaces to catch the light they need.

In terms of whether light placed beneath 24/7 will affect plant growth, depends on the plant, frankly - some plants are more responsive to certain wavelengths of light, and many plants need some hours of darkness. And yes, it is logical to assume that the plant will grow towards the strongest source of light, provided that particular light gives the right wavelengths and spectrum.

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  • Do you know how phototropism works if the plant is illuminated from multiple sides? It would seem logical that it would favor the brighter one; do you know of any issues with providing some light from below at all times? It'd make sense that most of the light must come from above, but do you know about supplementary light coming from below? – John Walthour Feb 19 '15 at 18:36
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    Can you expand your answer to contain whether the plants absorb light more efficiently from above or below? Thank you. – J. Musser Feb 19 '15 at 21:09
  • @J.Musser - that's the wrong question, coming from the wrong angle. I've added a bit to the answer for interest's sake, but there's not room here for a full botany lecture. – Bamboo Feb 20 '15 at 11:38
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    @JohnWalthour reflection helps also. Studies in sweet corn showed a 30 something % crop increase when there was crinkled aluminum foil sheeting under the plants reflecting light back up to the plants. – J. Musser Feb 20 '15 at 21:08
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    Simple version of plants leaning toward light: Auxins cause plant growth. Light disables them. In one sided lighting, the side of the plant toward the light will not grow much, while the other side grows faster. This of course tilts everything toward the plant. Of course, that's only part of it (the established leaves use a different mechanism – J. Musser Feb 20 '15 at 21:15

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