This question has been puzzling me, so I'm wondering if anyone can shed some light on it (err, sorry about the pun): If you have a large citrus tree that is relatively close to a structure such that the structure casts a shadow onto say half of the tree most of the year, but the rest of the tree was still getting full sun all year, would the part of the citrus tree in shade produce less fruit than the full sun part? Or does the part in sun absorb enough energy to make up for the part that is shaded? Similarly, would the north-facing side of a citrus tree produce less than south-facing?
I do not see a difference on my lemon tree that is on the NE corner of my house. Some of the fruit was in the very middle of the tree where it gets virtually no direct light. There was fruit right against the house as well as the part that is in the sun the most.
ChemicalX, interesting question. The portion of a citrus tree that is in direct sun for long periods of time, has little to do with the fruit production, or lack of fruit production, in the shaded section of the tree. Individual citrus fruit do not rely on the tree's full canopy of leaves, as their source of energy. Citrus fruit rely only on the leaves that are in nearby proximity, and not on leaves on the other side of the tree. Photosynthetic activity in the leaves nearby each fruit has long been known to influence the levels of the photosynthates (sugars and other carbohydrates) required for growth and taste. A still closer tie recently has been found between the photosynthesis in single leaves near citrus fruit , and sugars translocated into the exact fruit sections that are vertically aligned with the leaf. In other words, a nearby leaf that is just above the north west portion of a fruit, sends 90% of its photosynthates (sugars) into only the north west portion of that fruit. Further examination of individual juice segments within the fruit has shown that most of these photosynthates produced by the single leaf move into only one or two of the fruits segments that are also in alignment with the manufacturing leaf.. The portion of a citrus tree that receives the greatest amount of sun also has the sweetest fruit. Classic experimentation has shown the highest sugars were in fruit picked from the outside of the tree on the southeast, south, and west exposures. These are positions where light intensity and photosynthetic activity would likely have been greatest. Therefore, if you want to pick a very sweet orange, pick one that is growing on the top outside portion of the south, or southwest side of the tree. Picking one of the few fruits that grow in the shaded middle of a citrus tree, will be among the least sweet tasting fruit on the tree. Fruit from the north side of a tree will also have less sugars. The volume of fruit is also somewhat affected by the amount of sunshine available. But remember, it is due to the amount of sunshine received by leaves nearby each fruit, and not the general canopy. - Millet
Wow, that's a wealth of information! Very fascinating - so it's the quality/taste of the fruit that is affected, not the actual fruit production itself - makes a lot of sense. Thanks, Millet, that was very helpful! I will definitely keep this in mind when I plant the navel orange tree I just bought...
Sweetness is obviously not a factor with lemons, but I have not seen much difference in the amount of juice or size of the lemons associated with their location. I just picked a couple for a pie the other day from the center of the tree, a part that probably only gets indirect light-- those 2 lemons produced 1 1/4 cups of juice!
Skeet, I am counting on you to bring one of your Lemon Pies to the 2008 Citrus Expo in Georgia next November. See you there. - Millet
Skeet wrote............"but I have not seen much difference in the amount of juice or size of the lemons associated with their location."................ Skeet, that is because the juice content of a fruit is not a function of the leaves. Juice is a function of the transpiration system (xylem) and the root system's efficiency. Soluble solids, are a function of the leaves's photosynthetic system. - Millet
