There is not much shade in any citrus orchard......unless that provided by the trees themselves. And since commercial orchards are in the business of making money, if full sun actually deceased yields to any significant amount, they would be all over that issue!!

I doubt there is much to be concerned about re: sunlight. Although you could conduct your own experiment and see if shading one tree provided better cropping than those left in full sun.........

That's a good point that commercial farmers are in very sunny regions and are not shading their citrus trees. I'm in NY and Vladimir being in MA, I wouldn't worry about too much sun, as long as the trees are acclimated. If you're interested, put your trees in a place where the do not get late afternoon soon and see if anything changes. I do believe that there is a limit to the amount of sun that is beneficial and summer morning and noon sun is probably plenty, but I don't think in this region the extra sun causes any harm unless there is a rare exceptional heat wave. I'm no scientist, just my opinion.

My citrus are in containers. None of them get full sun. They are doing just fine. They probably get 1/2 day sun at the most. I think in full sun, plants in containers can be stressed from overly hot soil -- especially from about 11:00 am until 3:00 pm. Also a smaller root system in a container may not able to compensate for the high transpiration rate in a full sun location. Sort of depends on the health of the plant and the root system/size of pot though.

And again, it depends on where you are growing them -- what geographical region, humidity, quality of your sun and average cloud cover, haziness, latitude, and whether in the ground or in containers. I would think in containers in Phoenix in full sun would not be a good thing.

All that said, by mid-September, I am usually moving my plants to a location where they can get more sun and a warmer microclimate. That's the beauty of growing in pots I guess.

My Meyers and all my other citrus varieties are in full tropical sun; my Meyers produce around 300 fruits per year, so I doubt that is less than in other conditions. I know very well that for the Meyer, they can grow well enough in less than full sun; but the yield will be less. Don't know much about the other citrus varieties, as everyone here knows that I am a one trick pony.

As for the trees of commercial citrus growers being in full sun, I doubt that they could do much about it if they wanted to.

Silica, you make a good point. Actually, I would think they structures to provide shade. Obviously, the financial cost vs benefit is not favorable otherwise they would have built shade structures.

Also with tractors, trucks, sprayers, etc. it would be a real hassle to work under. About the research that the poster cited the results would depend on the location of the research. Growers already grow citrus to match the environment. Grapefruit in the desert, mandarins in the northern regions, lemons near the coast.

Sunburns are a fact of life in many citrus growing areas. The sun IS different depending on the latitude AND on prevailing atmospheric conditions. Guatemala John might not know this but sun radiation in med like and desert climates during the summer can be stronger than in tropical climates due to diminished air humidity.

Trees shut down in high temps and bright sun. All my citrus treeds grow much better in the off season inside under 23 watt daylight CFL's. 3/4 of their growth is over winter. I have a 6.5 month outside and 5.5 inside growing season. I have considered putting Low-E double glass windows that would block the infered between 11 AM to 4 PM to help with growing. To much work!

Citrus generally does Stop growing at temperatures above 95-F but not caused directly by the light. Put a citrus tree in a room and raise the temperature above 95-F a citrus tree would stop growing with or without light.

I have read studies that show optimal citrus growth occurs at 86F

After years of observation of my trees in a variety of conditions, citrus does fine or better as an understory tree. In my areas the late spring intense sun and spikes to 100F in low humidity burns the leaves.

I had a couple of days of 95F+ last week; after a cool spring. The trees in 1/2 day sun / morning are fine while those in full or afternoon sun look toasted. And those with the sunburnt leaves suffered the burn irregardless of marginal to excess hydration.

I would expect better performance under in a tropical (and humid) area and sun filtered by clouds.

"but sun radiation in med like and desert climates during the summer can be stronger than in tropical climates due to diminished air humidity."

This is so very true, summer sun in the mountain west or southwest or even the Plains is much worse than the South Florida sun in high Summer where there is greater cloud coverage, haze, intermittent downpours and the constant HUMIDITY is a physical entity onto itself, LOL.

My trees have been suffering from some sun burn, however, the trees are pushing growth in 106-109 degree temps to replace the burnt leaves with new leaves better suited to handle my desert sun.

The issue of excessive sunlight only applies to hotter climates, and applies more to younger citrus plants. Larger trees have a much larger percent of their foliage in the understory and partially shaded by leaves above them.

Another thing people may not be aware of, pomelos/grapefruits are more tolerant of intense sunlight than mandarins, while oranges are somewhere in the middle.

In hot desert climates almost any plant will benefit from 50% shade cover.

Mine probably get 1/2 sun like Dave...It works out so most get nice morning to mid-day sun, then shade, then some sun again depending on location. They seem to be very happy with lots of blooms and fruit.

Citrus grow well between 70 - 90-F. Below 55.4-F and above 95-F citrus trees stop growth.

Pranab, that is fascinating. I did not know why, but I instinctively have always watered my plants (and leaves) mid day if it is very hot to cool everything off. The 5-1-1 drains so quickly that I have never had an issue with overwatering. We get very hot temps here in MD (not like Evan), but hot and humid for sure.

From what I have read a lot of this has to do with root zone temperature, which may be a bigger issues for container growers. See http://www.crec.ifas.ufl.edu/extension/trade_journals/2011/2011_Nov_root_temp.pdf

I decided to do farther research into the citrus tree root shut down temperature of 55.4 F. The temperature translates to 13.0 C. This indicates to me that this test was done on the metric temperature scale but I was not sure. I thought about saying that this was a simple calculation that end up being 55.4 when translated xx.xC. For farther studies I translated 55.0F over to C and came up with 12.7778C. I them plugged in 56F and got 13,3333C. I got these numbers from google and guess that the 12.7778 was really 12.7777 forever and the 13 .3333 forever got simply truncate because the repeating 4 will alway get lobbed off with out affecting the previous digit. If this test were done in F the results would have been 55 or 56 therefore this test was done in metric.

Steve

Ike: Right, managing root temperature for containers is a significant issue. Unlike ground, soil temperature in containers can vary wildly. Black pots are the biggest problem. In spring and fall when it is cool they help to keep the pots warm. But in summer they get too hot. I have measured 120F soil temperature with about 90F air temperature just inside the pot facing Sun. With a clay pot about 95F. Not very scientific but gives an idea.

There are several ways I try to deal with it: dig the pots in mulch/dirt, shade the pot fronts with something else, pot in a pot method, light/white pots or clay pots and planting trailing plants in the pots.

And as Laura said, freely draining soil allows one to shower the plants frequently without worrying about root-rot.

Plants in containers are a lot more vulnerable to water stress and drought, especially when the containers are not big enough. They should probably be placed in partial shade, in places and times of the year it gets really hot outside. A lot of this depends on where exactly you live too.

The majority of my potted trees get mid day sun due to trees blocking the sun earlier in the day. They have full hot sun from 11 am to 4 pm and then are shaded by the house. They do show signs of stress by their new growth wilting. A bit of top watering resolves that fairly quickly, but I have noticed that a lot of my fruit has been dropping off. I am not sure if its from the heat or from being moved around on the patio.

I have a Eureka lemon from Record Bucks Farms that I have been struggling to keep alive for the past 2 years. It went into shock and dropped 90% of its leaves when I transplanted it right after bringing it home. Anyway, I have given it the same care as my other trees: full sun, regular fertilizer, and being careful with water. I saw a video on youtube and the host said the Eureka lemon does not like hot afternoon sun. I really didn't believe it at first after reading how folks here kept their trees out in full sun, but I do now. This Eureka has not grown any new leaves since it went into shock, but has put out blooms and fruit. This year I started giving it dappled shade. Then moved it into my sun room which faces north/northeast and gets about 1 hour of dappled shade. Well, damn. The tree started putting out new growth. I put it back outside in full sun and the new growth started to turn black. I put it back in the sun room and new growth is starting up again. I think it's going to stay in my sun room until all the foliage has grown back and then we will see about putting it outside.

From my experience with my Eureka, I think different varieties have their quirks. I thought all citrus trees liked full hot sun because that is what every source I have read said. I have come to believe hot sun is not good for anything living. I would give some shade from 1-3 pm if possible. My figs trees and tomatoes like shade after 2 pm and are loaded with fruit. Go figure.

Wow Denise. I am sortof seeing the same thing. I kept my Eureka (originally a FW choice size bought in the fall of 2016) in a due-NE facing spot last summer (due to getting the back patio situated when I first moved here) and it seemed to like that spot. Over this past winter, it got hit with some of the aphid issues that hit my thornless key lime and dropped most of its leaves but did give me fruit finally (that persist today).

When I put it outside this spring, I put it in a due east-facing spot, and it has popped out a couple blooms (at least one that appears to be forming a fruit), and I am finally seeing some signs of new leaf buds on the bare branches. My ST is right in front of it facing the same way. Meanwhile on the other end of the row is my new Shiranui mandarin that is close to southeast/south-facing, and it seems to be holding up okay with the longer duration of sun and is covered in blossoms. I have a plumeria in that corner as well and that is soaking up sun, literally from about 7 am till 3 pm. I have a potted fig nearby facing southwest and that gets similar (around 8:30 - 2 because the house blocks some). My Tango mandarin is sitting in the middle of the row (southeast-facing) bounded by the Eureka and the Shiranui "in the understory" of my lilacs and seems to be doing okay there. I have my Australian red centre lime over on the opposite side of the patio facing northwest since those were pretty much universally noted as being "understory" trees (and it is with all kinds of "understory" tropicals). The variegated pink lemon (Eureka) is in the middle of the patio getting some morning sun but when I have my umbrella up, it goes in the "understory" of that. lol

The back patio is on the northeast side of the house whereas my front directly faces southwest and is a nightmarish furnace in the afternoon during summer. I have a plastic urn out front with a rubra grass and am trying portulaca this year with it because everything else died in the heat there including supposed full sun/heat lovers like wave petunias and verbena that I tried in the past.