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Tropical plants may require a higher UV level in the light, if not to grow, maybe to fruit. Are there studies / sources on that with actual quantities?

Bamboo suggested in her answer to look at this page on UV strength, which I had seen already. It is slightly helpful in that it shows that, for instance, Germany in the summer can expect roughly half the maximum UV input as, say, Cuba, gets all year round.

However, the tropics don't have seasons, so a comparison would have to take into account seasonal differences in temperate latitudes. Also, while it does linearly relate to UV intensity, the UV index is adjusted for how damaging the UV is to human skin, so different wavelengths are weighted differently. This might be inadequate for thinking about plants.

Finally, while knowing the typical UV levels for a plant's natural habitat is a start, it would be better to know what irradiance it actually requires, how much, what wavelengths, what rhythm.

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Hanno Fietz
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  • I just noticed your reference to my comment, Hanno, using the term 'his'. Its not clear from my profile, but I am, in fact, female, though not really sure it matters one way or the other. – Bamboo Sep 10 '12 at 20:53
  • @Bamboo - you are absolutely right. My apologies. It may not matter with regard to the post, but still. Fixed that. – Hanno Fietz Sep 11 '12 at 18:19
  • Since blue light helps leaves and red light helps flowering, I would guess that ultraviolet light would more likely help the plant grow than produce fruit (since ultraviolet is next to blue in the spectrum). Infrared is close to red. So, if it's important, I imagine it's for growth. I could be wrong. – Brōtsyorfuzthrāx Oct 17 '14 at 21:10
  • Ultraviolet light is said to affect the nutritional value of the food produced by the plant: I don't think it's necessary for the life of most plants, generally, however. UV light can be a stress to the plant (but that's not all bad). It sounds like it might make hot peppers spicier (since stress to the plant is supposed to do that). This link is nice: http://www.ehow.com/list_6690390_effects-ultraviolet-light-plant_s-growth.html – Brōtsyorfuzthrāx Oct 17 '14 at 21:19
  • On the other hand, find out if plants reflect or absorb ultraviolet light. If they absorb it, there's a good chance it's useful for something. So, if you could detect UV rays and what plants reflect them, that might be helpful. When I invert my screen colors (using `xcalib -invert -alter` in Xubuntu) and look at plant leaves, they look a lot like a mixture of blue and red. Violet, which looks similar to a mix of blue and red (but is not actually a mix when it comes to light), may or may not also be absorbed. See this: http://scienceline.ucsb.edu/getkey.php?key=3155 – Brōtsyorfuzthrāx Oct 17 '14 at 21:30
  • On the other hand, a red plant like this looks green with its colors inverted (the inverted colors, if they are the true colors, are what it absorbs): http://www.rareseeds.com/early-splendor-/ So, it's likely that a green grow light might actually be good for this plant (while not doing much for green plants). – Brōtsyorfuzthrāx Oct 17 '14 at 21:35

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I have worked in and studied various greenhouses with a wide variety of tropical plants. As glass blocks most ultraviolet rays these plants would not have been receiving the same amount as they would in their normal environment.

Most plants will flower and fruit in a greenhouse if conditions are right. Some of the factors that are of greater importance are:

  • maturity of the plant
  • is a pollinator required or can it self fertilize?
  • amount of light received
  • being pot bound seems to encourage flowering
  • specific day length or change in day length may be required to initiate flowering

I looked for definitive research on this and could not find anything directly answering your question. There are many greenhouses around the world growing fruit and vegetables so it would seem that not all species require UV light to set fruit or seed.

kevinskio
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  • I can't find anything which gives a lux measurement either. Why don't you give it a go in your warm greenhouse and see how it does? And then let us know how you fare, I'm intrigued. – Bamboo Sep 09 '12 at 13:31
  • When you say "most plants will flower and fruit", do you have specific examples of plants that don't? – Hanno Fietz Sep 10 '12 at 20:12
  • @Hanno No specific examples, that was more of qualification. For every absolute in gardening there is an exception. – kevinskio Sep 11 '12 at 02:36
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You might find information contained here: www.uvawareness.com/uv-info/uv-strength.php to be useful. This site has an explanation of the uv index and how its measured, but its really aimed at sun protection for humans. Even so, it might make interesting reading for the answer you seek. I have no idea how to make it as a link for you to click on, thus proving indisputably that my skills lie entirely in the horticultural sector and not in computing/web skills.

kevinskio
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Bamboo
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  • Thanks, that's a page I had found already (should have written that in the answer, sorry). It does help a little, but not much. Will update my post to include what I found. – Hanno Fietz Sep 10 '12 at 19:54
  • Kevinsky, thanks for the edit - any instruction as to how I post a proper link in future would be useful. – Bamboo Sep 10 '12 at 20:18
  • Bamboo, there is a little icon that looks like a link from a chain in the upper left corner when you post a question or answer. There is some magical SE stuff that happens in a comment to convert links automatically. – kevinskio Sep 11 '12 at 02:34