I think early morning light, even fewer hours, is superior to scorching midday or afternoon light, which may shut the plant down for a period of time. Sunlight is quite important for production. In my oak-shaded garden, I get a reduced harvest of peppers due to less light (barely two hours of direct sun per day), but I'm content. My peppers also take a lot longer to ripen in the shady environment.

Josh

saood Saudi, hopefully, this link will cast some light on a heavy topic.

Thanks for the link Ronalawn. Yes this is a heavy topic. At one place this article says the light requirement in number of hours does reduce with increase in light intensity.

Doing some research on the net it was written that the maximum a plant can absorb is 1200 foot candles on a sunny day (which is around 10000 fc). Approx. 12%. However, when it comes to a cloudy when it is only 1000 fc, it absorbs almost all energy. Does this sound true? Do you have any experience in this field?

Saood

Citrus are plants known to require "direct sunlight". I have three small potted citrus on a south wall. My eaves are 40" long so they receive NO direct sunlight during the Summer at all. Lately, at the end of October, the pots are starting to get hit by direct sun but the sun will have to move lower before the plant gets direct sun.

They have grown just as much as the plants nearby that were exposed to direct sun all day. They are obviously getting enough sun from the indirect light of direct exposure to bright blue sky. Of course, Southern California inland valleys have very little overcast or even much clouds in the Summer.

I'm constantly moving my outdoor pots all around my desert landscape to experiment with sun/shade performance during different times of the year. My one constant is that I simply can't subject any pot to direct afternoon sun between April and October. It's too much even for "full sun" or "sun loving" types. In as little as 10 min, the soil heats up, roots begin to die off and the plant languishes. I suppose I could double or triple pot them, but I don't like the look and added heft/hassle of that setup. If I'm going to go through that much effort, it doesn't merit potting and can either go in the ground or I do without it.

Ox,
Are your plants the "full sun" plants?

I do keep them in full sun until the temps get above 90F. Would you advise against it?

Just yesterday I downloaded a couple of light meter applications (with above average reviews) on my android phone and today morning when I took the sun light reading for about an hour from sunrise. It was 12000 foot candles within 45/50 minutes? This is generally the reading at noon sun around the more northern places.

On the GW's vegetables forum, I am getting the response that its better to keep it under shade throughout the day and I am almost into November. Wonder what would happen in June/July/August :)

As I understand on vegetables forum that C3 type plants (i.e. most plants are C3) only use about 2500/3000 foot-candles of light and rest is actually resulting in loss of plant energy. Is there anyone over here who can share some comments / thoughts on it?

Saood

A search says Saudi Arabia is 24ð north, so south of Miami when comparing to USA. People in FL are unable to grow many veggies during the summer because of the heat/intense sun, and do things almost backwards from Z6-8 that you mention. Although you don't have the rain to compare to FL, your scheduling should probably more closely match how folks grow edibles in south FL.

Wow, you're getting pretty technical, Saaod. I now know whom to turn to for foot candle calculations. :)

A lot of mine are "full" sun - annuals, perennials, roses. An example is my smallish lemon tree in about a 15-20 gal pot. As a healthy, maturing tree, it would probably do ok in full Vegas summer sun planted in the ground (winter freezes would actually be the bigger concern here) with sufficient water, fert and care. In a pot, even a big pot, I got to keep it in the shade from 1pm on. Soil just gets too hot, leaves burn, trunk would probably scald. It gets all the sun it needs before afternoon to grow like a weed and thrive.

Keep in mind also the killer component of reflected heat off an adjacent wall or pavement. It's nice during the cooler months but a west-facing wall will burn up all but the hardiest desert plants in the ground and nearly 100% of any plant in a pot in that type of microclimate.

Ox,

When you do turn to me for foot candles calculation, I will give those with a disclaimer - "Please use at your own risk". I don't want a legal notice from you that I was the one who made your plants suffer :)

"Keep in mind also the killer component of reflected heat off an adjacent wall or pavement"

I took a picture this morning at 8 am of the my roof top gardening space to show it to you. The boundary wall of the roof and the wall of the tall building besides mine, will they really be a problem? Do they really add to the heat around the plants? I read the color also plays a role in the heat. As it gets closer to red and infra red the temperature rise. Yellow is closer to red - though mine is a a bit lightish one.

Thanks

Saood

I think as long as the container+plant is a foot or two away from a wall, you're fine.

How is that shade cloth working? Is there no way to put your pots in full morning sun and then full afternoon shade? An east facing wall perhaps?