Greenhouse shade advice needed.
 

Is 20% shade (light diffusing glass) enough at this time of year with peak ambient greenhouse interior temperatures in the low 90Fs and gentle air movement. I'm thinking of removing my 40% shade cloth, which in combination with the 20% light reduction of the light-diffusing glass puts the current shading combined at 48% of full sun. Is a 48% to 80% change likely to cause leaves to burn?



-Keith

If the air circulation is high it won't be a problem. Moving air carries the heat from leaves and allows them to stay at ambient temperatures.

High air circulation means everything is moving.

Keith, FWIW, orchid greenhouses I am familiar with in full sun in PA (Parkside) - with less solar intensity - typically had two layers of 30% in summer and one in winter. My greenhouse was partially shaded by a hillside and trees, so I went with 30% in summer and none in winter.

Parkside’s cover was 6-mil PE x 2, mine was 8 mm polycarbonate, and I don’t know how much intensity reduction your diffusing cover provides.

That's a major shade reduction when the sun is still strong and the temps are still high. My guess is that the plants would be fine with less shade but not at that quick of a reduction this time of year.

I have been trying not to get everything moving because I end up needing to water some plants more than once per day. I was already thinking I could aim the two ceiling-mounted circulation fans that blow above the plants slightly downward and leave my big floor fan on for more than only after bi-weekly watering. That would definitely move everything, so with your input. I will try it this weekend when I'm home - if it is sunny and hot.

Most of my orchid growing has been in either indoors or in moderate maritime coastal climates like San Diego, Seattle Washington and Brunswick Maine. Last fall when it got cool, I grew my Neofinetias outdoors on a table in full sun. I've been afraid to remove the shade cloth in the hot Mississippi summer because burned a few Phalaenopsis the first two years I was here in the spring giving them only early morning sun. Now, with the greenhouse, I could burn thousands of dollars of orchids in a day.

-Keith

---------- Post added at 06:54 PM ---------- Previous post was at 06:47 PM ----------


Ray, that's really great input. My greenhouse is an east-south-east facing lean-to. It is shaded from around 2:00-3:00 on by a sloped roof during the hottest part of the day. With 20% shade diffusing panels overhead, I may be okay, so long as I start with a lot of air movement and remove the shade cloth by sliding it up a couple feet in stages over a couple weeks.



-Keith

---------- Post added at 06:56 PM ---------- Previous post was at 06:54 PM ----------

My thoughts exactly. Better to err on the safe side. If I do it gradually the weather will be cooler by the time it is off too.

-Keith

I wouldn't drop the shade that much without strong air circulation.

Hi Keith - Here in NJ I am currently using 50% Aluminet shade.The greenhouse faces south/southwest and is a lean-to. In high summer I use 60%. By November I’m down to 40% with never less than 30% in winter. I keep the greenhouse cooler in summer with an evaporative cooler and a fogger. Fans along with the ventilation keep the greenhouse 3-10 degrees less than outside, depending on the humidity.

Agree. Here's my plan.

I have the fans needed to keep the air movement very high (everything moving). This will help mitigate potential overheating,until I find out how warm the leaves get in full sun. Then I can make a decision. Reduce the air movement if the leaves are not getting terribly warm, or wait and reduce the air movement as the weather cools further and the sun doesn't get as high.



Problem solved. :bowing - Thank you all.

-Keith

---------- Post added at 08:42 PM ---------- Previous post was at 08:20 PM ----------

You setup isn't terribly different. NJ is cooler than Mississippi, but you get your sun during the hottest part of the day.

My vent fan is crazy powerful so the greenhouse interior remains less than a degree above outside. Unfortunately, evaporative cooling doesn't work very well here b/c the humidity is almost always over 75%, and often over 85%. I'm planning to get a misting system for watering when I'm out of town, so I will be able to experiment with it.

-Keith

I made some light intensity measurements at noon today.

• Outdoors full sun (slight haze) - 7000fc.

• In greenhouse with shade cloth - 2750fc (42% of full sun). - This is lower than the calculated value of 50% (3750 fc).

• In greenhouse with shade cloth pulled back - 5000fc (29% of full sun).

My light diffusing glass is blocking 29% rather than the 20% specified by the manufacturer.

Checking the above figures using the 29% value for the glass and 40% for the shade cloth, the calculated value for glass + shade cloth is 43%, which is close enough to the measured 42% to be considered confirmation.

Conclusion: Removing the shade cloth should result in somewhat lower light levels that I thought, but the percent change will be the same.

-Keith

You know, no one (including myself) asked about the current status of your plants! What makes you want to make such a large shift in light reaching the plants? Are they doing poorly?