Citrus > Citrus General Discussion

So citrus trees are *not* generally ideally full-sun plants?

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--- Quote ---Maximum net CO2 assimilation of most citrus cultivars saturates at relatively low irradiance (600 to 700 umol m-2s-1), which is only 30 to 35% of full sunlight (1500-2200 umol m-2s-1) on a typical growing season day (Syvertsen, 1984). The excess radiant energy predisposes plants to photo-inhibition, heat stress and stomatal closure, resulting in a reduction in net photosynthesis (Pn), the ultimate source of fruit soluble solids.
--- End quote ---

Experimenting with grapefruit, they found no meaningful change in yield for using 50% shade cloth from Apr-Jul, but a 35% yield improvement for using 50% shade cloth from Jul-harvest.  A caveat that they encountered was that while reducing light levels was good on sunny days, on dimmer days it reduced the light levels down to below the plants' limits, and thus reduced photosynthesis. So "adaptive" shade might have been even better.

What's your experience with shading?  I had always thought that, with a few notable exceptions (such as finger limes), citrus trees were full sun plants that were significantly adversely impacted by shade.  But this argues otherwise.  Could citrus be effectively intercropped?

I noticed the same, too much sun doesn't make them happy. Sure, they will grow anyway but you can see the leaves are often showing sign of sunburn and discoloration.

Huh, this totally changes my image of citrus. I've always seen these big open citrus plantations with no shade and just assumed that it was because they needed full sun (and most plant descriptions say "full sun" or "bright location"). But the research says otherwise.

600-700 umol/mē/s is really rather low. Just checking on some other species - passionfruit tops out at around 1200, tomatoes peppers and bananas are unlimited by natural sunlight, cherimoya tops out at around 800, sugar apple around 900, etc.  Basically, it appears that citrus can *survive* bright conditions well, but just not properly utilize them.

Wild citrus are understory trees. With few exceptions...

Sylvain is correct, citrus trees started out in Asia as under story trees growing in the partial shade of the native taller trees.  I  have 7 in ground trees  (all different cultivars) and many container trees.  They all grow in full sun, I don't bother shading them.  It would be easy enough to shade container trees, if someone wanted to, but quite difficult to shade a fully grown tree.


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