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Missouri

I don't have a PAR meter, but measure photons in my gallons of sweat per hour. It sure is nicer under 30% shade netting from a growers perspective, but that may not always be what the pumpkin needs. Also, full sun may help keep pathogens like PM and others at bay.

7/24/2026 10:28:01 PM

Sunken Lands Arkansas

I would love to automate my shade cloth. I would like to know how long in the morning and afternoon do I hang out under the 400 because of shade cloth. Cooling effects of shade cloth may override loss of off optimum photosynthesis in the later part of the day???? you got me thinking.Good post!

7/24/2026 10:37:40 PM

Watlington, UK

It's a trade off. Lots of PAR means more photosynthesis BUT at the expense of possibly overheating and stressing the plant. Less PAR means less photosynthesis, but the plant is comfortable. Personally I would opt for the latter.

7/25/2026 6:08:59 AM

Connecticut

Hough- 30% shade actually can provide the near optimum amount of light that pumpkin plants can actually use. PM typically stars on the undersides of the leaves and other areas of low light intensity.

Swamp Foot- Most plants can not use the full light intensity so there are actually benefits to using shade netting. Automation is a good idea, but can be difficult to archive other than a greenhouse setting. I use a manual on and off approach with ropes.

Gerald UK- You are correct to an extent, and each plant species can have different tolerances. Take a fern for example, these are not high light intensity tolerant. Now, to giant pumpkins we want more PAR for more photosynthesis, but there is a biological limitation which is below the linear progression where more is better. There is a plateau curve so it is finding where that optimum level is for plant performance without giving more light than the plant can handle to only induce stress that will actually reduce yields.

7/25/2026 1:07:45 PM

Ma

Is it true that fruiting plants are only using somewhere in the 400-700nm range and of that even c4 plants can only process up to 6 percent of that solar radiation?

7/25/2026 3:07:07 PM

Connecticut

Country Boy- The 400-700nm are the wavelengths used in the highest percentage by plants. Some will argue the 300nm-800nm range should be used to take into account "all" of the wavelengths plants can use. This is what PFD (Photon Flux Density) measures. If you want the details here is a video... https://www.youtube.com/watch?v=um-3HZXFnc4

Regarding if plants can only use 6% of the solar radiation, I would say this is better represented as plants can only convert about 6% (on the high side) of light to biomass. Here is an article (at least the abstract and some of the intro for free) on this topic https://www.sciencedirect.com/science/article/abs/pii/S0958166908000165

There is also the CO2 limitation factor. The plants have plenty of light, it is really the CO2 that is more limiting, at least in the plant growth (not pumpkin growth) stage of development.

7/25/2026 9:07:41 PM