Citrus Growers Forum

Sven_limoen · Posted: Mon 26 Mar, 2012 12:03 pm

Last fall someone mentioned that citrus do not need a lot of sunlight to grow.
Since the spring has fully arrived it got me wondering how much direct sunlight citrus need during the day? Is there a minimum or recommended amount?
I'm talking about the amount of sunlight during spring and summer.

Greets!

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growing (at least trying): C. sinensis, C. latifolia, C. limon, C. mitis

Sven_limoen · Posted: Thu 12 Apr, 2012 2:47 pm

Must bump... Smile

Is this a very stupid question or a hard one? Smile

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growing (at least trying): C. sinensis, C. latifolia, C. limon, C. mitis

Millet · Posted: Thu 12 Apr, 2012 5:52 pm

All plants require light to produce their life's energy. Citrus belong to C3 plants, with photosynthetic rates lower than those of C4 plants. Even among
the C3 group, citrus are in the low activity range (together with other tropical and subtropical trees), being considerably lower than annual crop plants and lower still compared with deciduous fruit plants such as apple and grape. Photosynthetic activity of citrus leaves saturates at relatively low light intensities of 600 to 700 PAR which is only about 30 percent of full sunlight. Citrus is unable to utilize higher light ranges, to produce additional photosynthates. In citrus's original location the trees grew as under story trees beneath the higher canopy. The exact number of sun hours citrus require per day, I cannot say with certainty, but it would be less than that required by many other varieties of trees. I would naturally put a citrus tree in the most desirable location available for the tree, but if I had to say, 6 hours of sunlight should be enough. (Biology of Citrus) -Millet (283 BO-)

Sven_limoen · Posted: Fri 13 Apr, 2012 5:10 am

Millet wrote:

I would naturally put a citrus tree in the most desirable location available for the tree, but if I had to say, 6 hours of sunlight should be enough. (Biology of Citrus) -Millet (283 BO-)

That is 6 hours of direct sunlight without difference between 6 hours of morninglight/light at noon or eveninglight?

**I did red something about morning light being the most beneficial for plants. Don't know if this true.

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growing (at least trying): C. sinensis, C. latifolia, C. limon, C. mitis

Millet · Posted: Fri 13 Apr, 2012 12:06 pm

Sven_limoen, I don't think it is so much as the amount of direct light, or indirect light, but rather the total amount of light (photons) that hits the tree, either from direct, or indirect light that counts. Remember at only approximately 650 PAR (Photosynthetically active radiation) a citrus tree is making all the food it can. - Millet (282 BO-)

Evaldas · Posted: Fri 13 Apr, 2012 12:38 pm

Sven_limoen wrote:

**I did red something about morning light being the most beneficial for plants. Don't know if this true.

Well... Combining what Millet pointed out - that optimal wavelength of light for citrus is ~650nm i.e. the shorter waves of the red part of the visible spectrum - and the fact that in the morning there's more of such light (closer to sunset there's more of longer red waves (>730nm)) and due to the fact that citrus and all plants thanks to conversions between a few types of phytchromes (a type of pigment) register in what lighting conditions they are, it may be truth (but for citrus, not necessarily for all plants.)

RyanL · Posted: Fri 13 Apr, 2012 2:09 pm

It seems that citrus care for as many hours as possible but, the intensity is not as important as PAR(spectrum). Many citrus nursery will provide shade during the most intense parts of the day (between 11-2). - these light levels are enough to actually damage the tree and fruit. So a tree with maximum hours of sun + some shade at the most intense parts of the day may be most ideal. Over all, you want to give the tree as much as possible. more light = more fruit production.

Evaldas · Posted: Fri 13 Apr, 2012 2:14 pm

PAR has little to do with light intensity Wink

, it just indicates the color of light, similar to Kelvin ratings on light bulbs Wink

RyanL · Posted: Fri 13 Apr, 2012 6:18 pm

Evaldas wrote:

PAR has little to do with light intensity Wink

, it just indicates the color of light, similar to Kelvin ratings on light bulbs Wink

Evaldas, you are right my above comment is misleading in this regard. I will edit the post.

ivica · Posted: Fri 13 Apr, 2012 8:20 pm

Evaldas wrote:

PAR has little to do with light intensity Wink

, it just indicates the color of light, similar to Kelvin ratings on light bulbs Wink

PAR is normally quantified as µmol photons/m^2/second what is, roughly speaking, number of photons hitting horizontal surface of one square meter every second.
Counted are only photons with wave length in the range 400..700 nm
so one can say that PAR is a number of photons available for photosynthesis i.e. photosynthetically active radiation.

Some sources use Einstein unit i.e. μE/m^2/second.

PAR can also be expressed in energy units (irradiance, W/m2). Conversion is not simple (spectral integration).

Interesting results of the project "Photosynthetically Active Radiation (PAR) as Observed from Satellites" are here:
http://www.atmos.umd.edu/~srb/par/04status.htm

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Millet · Posted: Sat 14 Apr, 2012 12:43 am

Although citrus trees thrive in hot, dry environments, leaf photosynthesis has a relatively low temperature optimum. Temperatures of 77 to 86F (25 to 30C) are optimal. Temperatures of 95F (35C) definitely reduce photosynthetic activity. Extremely high light intensities, cause leaf temperatures to rise considerably beyond the ambient temperature, due to insufficient evaporative cooling. This rise in leaf temperature may also be involved in high-irradiation damage to the photosynthetic apparatus, of citrus leaves. (Biology of Citrus) - Millet (282 BO-)

Evaldas · Posted: Sat 14 Apr, 2012 7:27 am

Then I must've gotten it wrong Wink

. Sorry.