Good day, now that Spring has sprung in my area, the time has come to fight the pollen and start my new green house project. My new GH will be 12x24. It's made of that super thick plastic film. The side roll up in case it gets too hot. However, there is one thing that I will need to get----shade cloth. I sucribe to a growers magazine and they have a lot of shade cloth. Since my GH will be in full sun I'm trying to figure out how much of the sun do I need to blocked? 30%, 40%, 50%, 70%? For those of you with GHs, do you use shade cloth? If so, what percentage works best? I would love to have mine have a max temp inside of 90 degrees on a 90 degree day. Any ideas?

Dennis , If the sides roll up high enough and the doors are open would you need shade cloth ?

I would go with at least 50% and probably closer to 80%. You are going to have fairly high temps in the summer, where you don't been any solar heating. If you have never had a greenhouse, you will be surprised at how quickly you can heat an enclosed space that is in the sun. Think about how fast your car heats up, when you run into a store for 15-30 minutes (even if it is white or light color). Work it out so that you can put it on for summer and take it off for winter. Wheit is 80 outside it will be well over 100 inside.

When I built my little greenhouse it was great for about a week in the spring, and then the temps soared to 80+ and I was instantly trying to cool it off.  Misters really help cool things, and the higher humidity means the plants can take a higher temp. Get a fan to circulate the air, otherwise the temp gradient from top to bottom might be as much as 30 degrees, esp. in the cooler months.

BTW, it is March 14th, 10:30 and it is already 87F, 20% humidity and a 10-20 mph wind. So always plan on the unexpected when working with a greenhouse.

It would be a shame to block all that light just to keep temps down.  I'm thinking of doing a temporary one for spring until frosts are no longer possible.

Last summer I struggled to keep temps down in mine. I used a very large exhaust fan with intake on the lower north side of the greenhouse, which would keep it around only 10F higher than outside temps. Without the fan, well, it was 50F here last week and got to 110F in the GH.

I've got a 60% shade cloth on my 10 X 18 greenhouse / hightunnel. Without it, it was so hot in there you couldn't stay in there for more then 10 minutes at a time, even with the sides rolled up. The tomatoes I had in there didn't do well, as they were stressed from the heat.

Added a shade cloth an you can hang out in there all day, plants love it and it provides plenty of light.

This is what I have.

https://www.greenhousemegastore.com/product/60-percent-aluminet-shade-curtain/shade-material

Hi Dennis,

I used 50% and 60% aluminet on my greenhouse.  I really helps keep the sun off and the greenhouse cooler.  It is $$$ than the plastic types.

Are you guys placing it on the outside of the greenhouse or hanging it inside?

Kerry, down in my country, every comercial nurseries with a GH has shade cloth on top. I asked most and most can't remember what percentage they have. The catalog I have recommend 90% so looks like Jon's right. Every nursery that's I've visited had shade cloth and it was hot as heck inside. The kind I'm getting comes in percentage of 30, 40, 50, 60, 70, 80, and 90. They recommend 90% for green houses but I wasn't sure it that was too much. Jon recommended 80%. At first, I was leaning towards 70%. But I think I'm gonna go with 90. But before I do, I'm gonna go by my friend's place and ask him.

Usually greenhouses with shade are for foliage plants and creature comfoth. I don't know of a single farmer that has a shade on a vegetable transplant house. You can't do what a retail nursery does because they are just maintaining them. Most of ours are sold with 50 percent and my recomendation is that while it in a bag to hide it. I'm just a contractor.

Thanks Hersell! I was hoping you would chime in. So, what do you recommend? 40%?

I prefer the aluminet, it is cooler. 8 hours of sun is plenty and as you said we have an adequate supply in the south. 30 or 50 would be plenty. I don't use but it's just personal I guess. I learn to work in my houses in the mornings and evenings and don't look at the thermometers at mid day.

Dennis , I based my question on my experience vegetable farming in southeastern PA.
There we had similar sized tunnels to yours - 4 that were 14x40   - 2 that were 14x76  and a 30x96.
Growing greenhouse tomatoes , peppers , european cukes , eggplant etc for a 220 family CSA.
We never used shade cloth on any of the houses even though that area has a very hot and humid Summer , the peak hot months of which reminded me of where I grew up in Georgia and Florida.
If we had the doors wide open and high roll up sides (6 foot roll up sides on the 30x96) the temps were fine for all those crops.
I was guessing that with very good natural ventilation the figs would do just as well without cutting down the light.
On the narrow houses like 14 footers , the ones with tall sides, rather than those single piece ground to ground hoops, allowed for much better ventilation with higher roll up sides while still retaining the benefit of rain protection .
I'll be very interested to see what you decide after your research into this.

I used 30% for walls and top in my commercial nursery operation to protect plants from strong winds and ocassional hard down pours. No plastic sheeting.

I only put it on the top and west side.

Different applications require different percentages. Growing established plants is quite different than starting cuttings, recently transplanted cuttings, etc. Light wasn't an issue with the cloth on the top - it was all about heat control.

Dennis,

There are lots of recommendations on shade cloth based on what you are growing.

For winter I used Aluminet inside the greenhouse.  I had it set up so at night I could keep the heat from going up to the top of the greenhouse and being lost.
Mostly you do NOT want shade cloth outside the greenhouse if you could get snow.  The shade cloth will not let the snow slide off the plastic and it can crush your greenhouse.

For summer I used 3 shade clothes to create 3 zones.  40%, 50% and 60%.  If I was getting shipments (ship rather than air) which were stressed than I would toss up another 40% or 50% to cut the light way down then gradually pull it off.
If you double shade clothe say 2 50% you do not get an 100% shade.  The first gives you a 50% transmission ad the second will give you 50% of the 50% light so it would be about 25% light.

Pino,
I used clips, rope and stakes to hold the shade cloth.  Stayed on through hurricane Sandy so I must have done something right considering that house was in NJ.

Thanks guys and gals! Aluminet is cheaper than the stuff I was going to buy. I did no know you guys installed it inside your GH. That will work best for my little 6x8 GH.

Wow what were you going to buy.  The only thing I know that is more expensive is from Ludvig Svensson.

Due to the large number of small farms in the area, there are wholesalers here who have machinery to produce large (and enormous) shade cloth in custom shapes (straight edges) at various percentages, with grommets sown in at 1 foot intervals. The cost is incredibly competitive for sizes 1000 sq.ft. on up -- 50k sq.ft. is not uncommon. Typically these are adhered to either PVC or galvanized steel tubing with "outdoor" zip ties. A good thing to know when purchasing shade cloth with pre-installed grommets is that it stretches. When ordering from a production site, tell them the dimensions of the frame plus the desired shade percentage and they will produce something that stretches to that size. One supplier in the area is Wind & Shade Screens in San Marcos. Please don't think of them as an internet ordering site. Instead, whatever you order might take 6 weeks before its your turn in the production schedule. They do hire (and charge you) for deliveries in the local area. Otherwise shipping is usually your problem.

Thanks Richard.  Sharon, my new GH will be here next week so, I'm scrambling trying to learn all this before it comes.  I receive a Grower's Outlet catalog and was planning on ordering from them.  I will need this cloth for both my old 6x8 and my new 12x24.  I got some last year from a guy.  I think it's 70% block.  Just today, I noticed that Northern Tool has some for my GH.  It's $49 bucks.  Is that expensive?  I ask b/c I really don't know.  My current GH is made of aluminum with a green coating.  It's cute, but I've outgrown it!

Been sick with the flu....and now that it's about over, I decided to pull out my shade cloth and see if it makes a difference inside my current GH.  This cloth blocks 70% of the sun.  It's 10x12x20.  At high noon, its 72 degrees outside in the shade.  When I placed the cloth on, the inside temp read 98 degrees.  Now, 90 min later, its 87 degrees inside my GH.  My new GH will be installed right behind this one as soon as I start feeling better.

Nice Dennis
Best of luck with it. Happy Easter

Lesson 1.  Make sure you have the right Shade cloth--get 90%!!!!
After growing figs inside my GH this year, the 70% shade cloth wasn't enough.  Jon was right!  I should have purchased 90% shade cloth.  What I learned is, even though the product says it blocks 70% of the sun, it's really blocks 30%.  When temps reached 100 degrees this year, the sun still came through the shade cloth and my trees struggled.  The air quality wasn't the best and neither was the soil mixture.   I ended up pulling many of them out.  I bought more cloth but now I completely understand the importance of getting the right cloth.  

Lesson 2.  Get rid of perlite 
Trees with loose soil with a lot of perlite suffered the most.  I had to water them twice a day and 3 times when temps got over 100.    Trees in pure compost never had a problem.  This is why going forward, I will never ever up pot my trees with perlite or any soil less mix with perlite in it.

Lesson 3.  Cheap black nursery pot hold too much heat
Trees in black pots BAKED inside my GH.   Trees in SWP did the best.

YOU BET!