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Quantity Vs. Quality of Sunlight

Posted by saood Saudi - 10b (My Page) on
Sun, Oct 20, 13 at 4:43

Many of the fruiting vegetables require full sun (atleast 6 hours of direct sunlight as they define it). However, I was just wondering if the intensity of the sunlight also has any effect on reducing this requirement? In a desert climate of Saudi Arabia - even in October - the sunlight is so intense that the leaves burn if not shaded. I have time and again read that vegetables plants prefer / appreciate shading in desert climates but then this raises the question as to how the sunlight quantity requirements (of atleast 6 hours) gets fulfilled to produce a comparable output with that of more moderate USDA zones (6-7-8)?

Whether this 6 hours requirement is for places where the intensity is moderate or is is applicable to vegetables grown in any climate zone? Can plants growing in desert climate work as good with 4 (or lesser) hours of direct sunlight compared to 6-8 hours of sunlight in more moderate climates? Can the intensity of the sun compensate for the reduced number of hours of direct sunlight? Is there any sort of scientific explanation for this phenomenon?



Follow-Up Postings:

RE: Quantity Vs. Quality of Sunlight

I cannot answer for desert climates, but I have found that if you have early morning sun until 2/3 o'clock in my zone 7, you can grow almost anything. I unfortunately have mostly shade with afternoon sun which I think is the sun in the morning and then things get blasted with hot afternoon sun.. With afternoon sun of 5/6 hours you can have roses, vegetables, etc, but there is NO comparison for full all day sun for those kinds of things...

RE: Quantity Vs. Quality of Sunlight

I was reading a book by Larry Hodgson called "Making the Most of Shade." Although I didn't agree with everything in his book, I was intrigued by what he called the "Petunia test." The test involves planting petunias here and there in the shade garden to see whether they'll bloom. He said that if a petunia will bloom even weakly in an area, then that indicates a part-sun situation. He suggested using the test to determine whether some plants might bloom in an area that's thought to be shady.
I live in Colorado, where sunlight is more intense than it is in other areas of the country. I thought I would give the petunia test a try next spring to determine just how much sun I get in various areas of my shade garden. You might consider doing the same in your area before investing in more expensive plants that require at least part sun.

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