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Author Topic: So citrus trees are *not* generally ideally full-sun plants?  (Read 900 times)

KarenRei

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https://fshs.org/proceedings-o/2001-vol-114/177-181%20(JIFON).pdf

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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.

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?
J, g er a rkta surnar plntur slandi. Nei, g er ekki klikku. Jja, kannski...

00christian00

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #1 on: June 06, 2018, 06:41:14 AM »
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.

KarenRei

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #2 on: June 06, 2018, 07:10:10 AM »
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/m/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.
« Last Edit: June 06, 2018, 07:13:36 AM by KarenRei »
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Sylvain

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #3 on: June 06, 2018, 08:02:49 AM »
Wild citrus are understory trees. With few exceptions...

Millet

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #4 on: June 06, 2018, 11:28:56 AM »
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.

z_willus_d

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #5 on: June 06, 2018, 11:33:54 AM »
All of my citrus are in containers.  I found that as the trees grew larger to fill there 40-gal containers, they became harder to water.  In the hot Spring, Summer, Fall months, I would have to pretty much have a constant drip (w/ soakers under mulch) running for the afternoon hours.  I had a lot of fruit drop due to this (even mature fruit was dropping and/or splitting).  After moving to a spot where the trees only saw morning to early afternoon sunlight (and were shaded in the later afternoon), the plants started doing much better.  I do think they suffer in the energy and photosynthesis side somewhat from their limited ~6 hours of sun, but it's worth the trade-off.  For trees planted in the ground, I would think that it would depend on how scalding hot the sun gets during periods when the tree is pushing out new leaves.  Also, how well they can be irrigated.  Younger trees likely benefit from the adaptive shading.

KarenRei

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #6 on: June 06, 2018, 11:43:45 AM »
This is really great for us.  In the summer we have lots of light, but spread out over a long day rather than concentrated around noon. At other points in the year, we choose however much we want to supplement and for how long of a period of time.  Should make it a lot easier to achieve good production.
« Last Edit: June 06, 2018, 11:52:34 AM by KarenRei »
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laidbackdood

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #7 on: June 06, 2018, 01:10:36 PM »
I have found the same here in Perth.......In the heat of summer i place my containers so they get morning sun only....until 1pm and then they are shaded........I have three trees that receive little sun in my courtyard with roof cover and dappled light and they all look healthy........I have mixed results with the 4 i have in the ground that are in full sun.......i reckon they need gradual conditioning to full sun...........In winter time.....the sun sits lower........so i move my trees closer to the house......and under the eaves........they still get the same amount of sun but boy does it rain through winter here.......its rained for the last week...every day......My newly seeded lawn is going for it !
I find the only trees that like full sun in perth are mango"s and Papaya.

SoCal2warm

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #8 on: June 07, 2018, 02:01:42 PM »
A lot of this is totally climate dependent. In the hot dry summers of Southern California, plants tend to do better in a little bit of shade. Even plants that are said to do best in full sun. Somewhere further North with cooler temperatures, more sun is better.

In Iceland I definitely would not worry about citrus getting "too much" light.

Mike T

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #9 on: June 07, 2018, 03:42:22 PM »
The article is pretty general and doesn't seem to consider temps, humidity, wind and UV index or that full sun adapted plants often close stomates. Various citrus have different climate preferences as well and might perform differently when shaded in different places. Less sun might also make trees more prone to fungal attack also.
The waxy leaves of many citrus are not typical of understorey plants with a few exceptions,
My ones that get shaded get more fungal attack and get taller.Citrus just seem to prefer full sun even in a warm climate.

Millet

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #10 on: June 07, 2018, 03:48:45 PM »
I suspect the increase or decrease of crop potential, is more of a University thing, then a commercial growing situation.

Lory

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #11 on: June 08, 2018, 05:52:34 AM »
My 1 cent experience:  in Cebu island Philippine 9.9 N from the equator: lemons and mandarins perform MUCH better in partial shade/filtered sunlight than in full sun.
I didn't notice any difference for pomelos since all my trees are in open soil / full sun.
I'm from Italy and at my latitude all citruses are typical FULL SUN/south  exposure trees.
But there it is 45N way different from here were equatorial sun can be really scorching!
Lorenzo

KarenRei

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Re: So citrus trees are *not* generally ideally full-sun plants?
« Reply #12 on: June 08, 2018, 10:06:43 AM »
Indeed, ~2200 umol/m/s is cloudless sun directly overhead. Your typical blazing tropical dry season sun, your typical desert summer sun. Any clouds, even wispy ones, and any angles, reduce this. 

That said, if these studies (there's not just one, multiple come up with the same number) are correct, then it's not just an issue that citrus gets stressed by full sun - it's an issue that citrus can't use the extra energy at all, regardless of how much stress there is on the plant.  The sun can only add stress.
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