What type of GH plastic to use

[Rajun Gardener]

I'm in Louisiana and only grow in it from November to about early May. I found a place that I think has good prices but the options are "Too Many".

Hopefully someone can point me in the right direction. I can google for answers but I want experienced growers to chime in.

Here's where I'm looking, it seems the prices are fair but I'm open to recommendations.

https://www.agriculturesolutions.com...lastic/dirDesc

[Cole_Robbie]

The clear stuff is probably fine for you. It tends to heat up the fastest. 6 mil is standard and plenty thick. I have the clear on my greenhouse, Sunmaster brand, and it is finally falling apart at the seams after 5 years. Almost all film now has condensation control, which means water runs down the plastic inside instead of dripping off.

Here's what I have on the high tunnel:
https://www.hummert.com/product-deta...-uv-clear-film

It says clear, but it's really not, it's opaque. It does not get as hot, which is good for me, trying to grow tomatoes til June or so, where it can get to 90 degrees outside temp.

Here's a site with some great prices on film: https://www.growerssolution.com/
They had free shipping for a while, not sure if that's still going on.

Choice of film is not as important as your ventilation setup. Keep in mind that almost everyone underestimates how hot it gets inside on a sunny day with calm wind. My greenhouse can run 50 degrees above the outside temp, and that's with just February sun....in Illinois. You want big doors that you can prop open and roll-up sides, or some sort of side vents.

I know a guy who is a market vendor and a very experienced gardener. He went to an extension center talk about greenhouses, where they told him roll-up sides were optional, so he didn't include them in his design....and then he cooked all of his plants.

So go for overkill in regard to ventilation; that's my advice. You will need more than you think you need.

[Rajun Gardener]

Thanks Cole, plan B popped up.
A friend reminded me to try a local nursery for some used plastic. I called and talked to the guy and he had old plastic used for 1 season for sale for $15. It's 40'x80'. He said it's too hot so they just use it in winter then remove it and try to get a few bucks off of it. This place is huge, 84 acres of greenhouses and nursery. I snapped a few pics and still I can't do it justice, they have just about every plant you can think of.




Those are all greenhouses in the back.




They sell tropicals too, look what I found


They're right next to Rip Van Winkle Gardens and the flowers are still blooming



Joseph Jeffersons Mansion

[Cole_Robbie]

$15. It's 40'x80'

That seems too good to be true. Are you sure it's not a film with a 1-year rating? Typical 6-mil is rated 3-5 years. A new piece that big would be $300-400.

Thanks for sharing the pics, though. It is an impressive operation.

[Rajun Gardener]

It might be a film but for the price how can I pass that up. I unrolled it and it was only 32' wide but 150' long. Can I fold this up and save it for future years if I keep it in the barn and safe from mice? I'm not sure how the 4 or 5 year plastic thing works, is that in full sun or does it mean it will break down at that time?

Here's a pic of it after I unrolled it.

[Cole_Robbie]

Mice don't bother my plastic. I have piles of old stuff everywhere.

The ratings are for year-round full sun, but of course sun intensity varies by latitude. When they make greenhouse plastic at the factory, the original rolls are 10-12' wide. Larger pieces are made by heat-seaming it together. Those seams will be the first part to fail.

[AlittleSalt]

Not that I have ever used the plastic on a greenhouse. The 4 mil stuff didn't last but 6-7 weeks on the ground for solarization. The 6 mil did a lot better.

That might be comparing apples to oranges though.

[PhilaGardener]

I'd roll around a plastic pipe for storage out of the sun. Folding will generate creases that might weaken. Great project!

[Rajun Gardener]

I finished the plastic just in time for this front last night, we only got to 38. Here's my repurposed wood GH, it's not perfect but will work for my needs. I was able to fit 20 dutch buckets with room for a few other plants.

[Cole_Robbie]

Your carpentry looks really nice, as does the bucket system.

Everyone who builds a greenhouse for the first time will underestimate the amount of ventilation required. I went through it, too, so don't feel like I am singling you out. You're going to want to improve it in that regard. A big window or door on the opposite side of the existing door would help a lot, creating a cross-breeze.

If you have a heat emergency, throwing some mud over the top will cool it down. If you're at the end of your season, you can use diluted white latex paint, but it's not coming off, even with a pressure washer.

Also, one of my greenhouse suppliers is adamant that contact with treated lumber will corrode greenhouse plastic. I haven't seen it happen yet, but it's something you might watch for.

Good luck with everything.

[Rajun Gardener]

I'm aware of the heat it builds and quick too. I had problems with the old small one I bought off of ebay. I'm trying to figure out how I want to vent it. I see harbor freight has the automatic opener, have you used those before, do they work? I also have an idea for a fan. I have a new extra bathroom vent fan that I can mount at the top and vent it outside with a flapper valve that closes when it's not running and use an attic fan thermostat to control it. I checked it earlier and had to open it up, it went to 90 but cooled quick opened up. I think I'll have to get used to this one because the ceiling is so high up and that should help with the heat some. I'm also thinking of using another bathroom vent to blow across the reservoir to warm it up during the day.

I ran a small heater inside this morning because it got down to 38, I might set that up automatically too. I'm still kicking ideas around.

I asked a few people with greenhouses and use PT for the baseboards and none of them had a problems yet and it's going on 3 years.

[Cole_Robbie]

I've never used the auto openers. I would trust them more with a cold frame or smaller structure.

Don't waste your time with the bathroom fans. They're a joke. If you want to move air, get a real blower, like the ones used to dry floors.

Here's an amazon link:
https://www.amazon.com/s/ref=nb_sb_n...3Afloor+blower

It's cheaper to let the wind do your venting, but you'll need a cross-breeze in both directions. Even with my sides rolled up and big end doors open, I still have to throw mud on top in June when the temps hit the 90's, or else it is 100+ inside and the plants die. You might also fashion a shade cloth for yourself to throw on there when you need it. A couple old white bed sheets over the top would help a lot to keep the temps manageable on a hot day.

Similarly, if you want to heat the structure, throwing some sort of tarp over it as a second layer would help tremendously. The R-value of greenhouse plastic is pathetic. It doesn't hold heat at all.

[Rajun Gardener]

I'm gonna try a shade cloth this season, I follower a few growers in Australia and they grow hydro peppers under a shade cloth because the sun is too hot. I have to try something for the tomatoes to grow.

I have some old windows I can install but really I want to be able to take the sides off completely in summer time. I installed the plastic in pieces for that reason. I thought about using 2 layers of plastic to inflate it but I think it's a waster of time and money here. I'll figure something out tomorrow, after tonight the lows will be 40-60 for the next 10 days so I need to do it quick.

[Cole_Robbie]

Here is a useful link:
http://www.builditsolar.com/Referenc...s/HeatLoss.htm

The R value for 6 mil plastic is .6 and an inflated double layer is about R1.6 I think. Using the calculator will make it sink in how difficult it is to heat a greenhouse. The best design I have seen is Chinese. It's only clear on the south side, and they roll a big insulated blanket down every night and back up every morning. For my greenhouse, I have to build a little low tunnel around the plants, drape that in plastic, and put the heater under there.

[BigVanVader]

In my climate the only way to keep it cool is roll up sides, vents in both ends and shade cloth.