Does anyone know what a guideline is for the minimum amount of sun a citrus plant can get and still be healthy? Everything that I have seen says full sun.

Can I have a tree in a 4 hour sunny position in my yard and not kill it eventually?

The short answer is yes - if other growing conditions are met. There are some unstated factors that will impact the health of your tree such as.

1. Time of day the sun shines on your tree. I consider morning sun better.
2. Degree of shade the tree will be in. All shade is not equal.
3. If the tree is under other trees, what kind of trees are they? Do they have lots of surface roots? Cast deep shade or dappled sun?

Generally speaking, the more sun, the better for the health of the tree.

Ned

From what I have read and my experience with my shade cloth nursery, citrus do not need full sun at all--the maximise their photosynthetic potential at about 30% of full sunlight (650 PAR --full midday sun is about 2200 PAR). My seedlings under a shade cloth (estimate about 50% shade) have done well and even produced flushes during winter (due to black plastic pots and slow release fertilizer).

Time of exposure to at least 650 PAR is probably most important.

Thanks Guys! I will do some homework today to see how much sun and when my side of the house gets.

The shadow of the house is there until about 1pm and I have full direct 2200 PAR sun till about 5pm. More during summer.

I have one tree on the west side of my house that gets about the same. It is flowering and appears to be doing fine. I don't think I ever measured the light intensity in the shade of a building, but I bet it is higher than you would think--my guess would be in the 400-500 PAR range and that is well above the critical compensation level where photosynthesis is equal to respiration.

When people add lights at night in winter to extend the growth period, the PAR value is probably less than 200.

Skeet's point about the PAR value of lights used for night lighting of citrus is interesting. While it all depends of the type oflighting used, I think ithe PAR value would be higher, especially when a HID light system is used. However, I do not know, but I am going to look into it. - Millet

Millet, we had a growth chamber at work with 8ft fluorescent lights almost next to each other (probably 2 in centers) the PAR reading in the chamber was in the range of 200-300 micro moles/meter sq/sec at the work bench level. In a typical lab where I worked, the meter would read 20-30 PAR.

The thing that amazed me most was the amount that light was reduced by a really dark cloud--PAR would drop 90 to 95% --but that was still way more than we worked under indoors.