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phoenix AZ

I have been reading and thinking about light this morning. I realize the main reason that there is a golden pumpkin growing belt at certain latitudes is because this area has the right blend of low intensity light for long periods of time during the summer. Us southern growers have days that are too short and to intense. I have been trying to learn about ways to raise the amount of light our plants get while lowering the intensity. There are two types of light direct and diffused. Direct comes from the sun. My basic understanding is that diffused light is just light that is scattered light over a broader area. A lot of articles I was reading say that plants grow better under diffused light because the light hits them from more angles, and can get places like under the leaf canopy that it otherwise couldn’t and actually raises the total amount of light.

1/6/2010 8:24:30 AM

phoenix AZ

Now to my questions. Sorry if the post is too long. I don’t expect anybody to answer all of them but maybe somebody wants to share their input.
1.I have seen many greenhouse type products that claim almost 100% light transmittance and yet they still diffuse the light. Why would people not use this more. It seems like if you could still get the same amount of light and yet it was diffused it would be better for growth? Some studies I was reading talk about 20-30% increased yield with diffused light.
2.Other than heating does direct light have any benefits over diffused?
3. I see that many people have had good results with sun shades the main point of the sun shade is to reduce the heat by reducing the light right? People don’t necessarily want less light, they just want less heat and a way to do this is by reducing light. Is it straightforward that as you reduce the percentage transmitted you reduce the heat, or are there materials that can reduce the heat while still allowing higher levels of light through
4. Wouldnt it be better as long as you could keep the temperature cool enough to use a type of shading that allows all of the light through, and yet diffuses it, so it doesn't burn rather than using a shade cloth that blocks 50% of the light?
5. What material diffuses light best?
6. Is there a downside to diffuse light?

1/6/2010 8:24:48 AM

Clayton, Ohio, USA

This might be of interest to you.

http://www.igcusa.com/greenhouse-shade-cloth-aluminet.html

1/6/2010 8:48:57 AM

Anchorage, Alaska

Since light is energy, more light will always yield higher temperatures. You can choose materials which allow the heat generated to escape more or less readily, but you can't have both more light and less heat.

You can reduce the temperature on your leaves by eliminating green light which is not in significant use by plants. A green plastic row cover is one example.

Diffused light can be beneficial because it spreads the light over a broader area, possibly illuminating an otherwise shaded area of the plant leaf.

If I were trying to increase diffused light, the first thing I would do would be to use _aluminum mulch_. My second idea would be to mount what I call a "morning mirror" which faces the east and is on a tall post west of the patch. It could be used to get a jump start on evaporating the dew, and brightening up the shaded portions of your leaves.

There is no downside to diffused light, but there will always be a downside to how you achieve it. Like any new idea; test, test, and test again. (Less air flow, insufficient light, too much moisture are possible problems)

1/6/2010 9:52:18 AM

Little-TON - Colorado

Mirrors would burn the leaves....acute right angles of remember how we can start a fire with a mirror........(MHO) Usings a flat white reflector would diffuse and provide a cooler light...believe it or not provide a better reflector for plants than a mirror. I have tested this out....A flat white works better than a mylar reflector. Most plastics that are used for diffusion end up breaking down due to the UV and changing over time. We believe that using shade cloth reduces over the chart weights....just a gut feeling at this time....Grow naked....risky...Yes.....But oh so much more fun......

1/6/2010 1:48:27 PM

Anchorage, Alaska

The Wiz is right. Silly me for not doing the research.
Do you use reflectors?
Is the entire patch covered by shade cloth?

1/6/2010 4:40:21 PM

South Bloomfield, Ohio

Langevin's latest book shows the pumpkin growing belt according to sunlight.

1/6/2010 8:42:04 PM

phoenix AZ

Last year I wrapped some plywood in emergency blankets for reflection and tried to avoid the shade cloth until it got well over 100. This year I think I will try some plywood painted with flat white instead of the mylar, and maybe some type of plastic plexiglass or film well above the pumpkins that can diffuse the light without burning them up. The problem is I have to start the pumpkins now to beat the heat but the days are only 10 hours long.

1/6/2010 9:40:06 PM

Las Cruces NM

Being in NM, I too have been thinking sun and heat. The first problem with saying just sun/latitude is microclimates (take a look at a zone map) and we know high altitude are cooler even though it gets the same sun. I think pumpkins can take the sun, they just can't take the southern heat! Northern growers advise as much sun and heat as possible, but in the same breath note temps above around 80 having negative effects. It is our 100 temps that are the killer -- throw sun on top emphasize the heat. That is why southern growers use shade cloth -- to cut down on leaf temp. And start em early to avoid the heat! It double blade as sun is also what produces the carbs that go into the pumpkin -- the long summer days is likely to produce more daily carbs = the orange belt. Diffused light probably hits more chlorophyll. Yea, I thought about blanketing my path with HID lighting for half the night but I'm not that crazy ... well, the fact that I thought about it might mean I'm getting close LOL.

1/7/2010 12:50:29 AM

Midway, UT

I agree that sun (although important) maybe isn't as big a factor as temperature and temperature swings in growing big pumpkins in more extreem climates. If these plants could have 85 degree days and 75 degree nights every day they would be happy. 95 degrees down to 55 at night just doesn't agree with the plants very well. They don't seem to like big transitions.

1/9/2010 11:24:01 PM