Is using milk jugs as my water sun collectors even feasible?

So I don't want to take up a lot of space in the greenhouse with big water tanks. I do have access to loads of plastic milk jugs though and they'd fit nicely in between the back wall frame. However, I'm not sure if the jugs would be large enough to make a difference. Opinions please. Not trying to plant things in winter but just keep the greenhouse an even temp during growing season.

Here at the 47th parallel, our summer sun has a UV intensity (I think that's it) that bleaches clothes in a couple weeks and destroys plastics. Garbage bags, tarps, shopping bags become brittle and fly apart at a touch. So do milk jugs, so it depends on where you are...but you don't want to clean up fragmented denatured plastic.

I was coming to say what Fredy just said, about intense sun -- except here it's year round! I had never seen plastic degrade so fast before. That said, I reuse a lot of plastic containers, buckets, grow pots, etc and I've found that just covering them up from the sun works wonders (literally, throwing an old sheet over the jugs would work). I keep old feed sacks for wrapping around plant pots that need to stay in the sun. They break down but the pots seem to last longer.

I've seen that done.  I think the smaller containers give the benefit (or disadvantage) of shorter thermal cycles.  While a 55 gallon drum may average out temps for a few days, a 1 gallon jug may do it for hours.  So they probably wouldn't get you through two cold days in a row but they should help on every cold night.  

Where I've seen them used, they were painted black.  I'm not sure if the paint protected them from UV degradation but it likely helped them collect more heat.

Fredy Perlman wrote:Here at the 47th parallel, our summer sun has a UV intensity (I think that's it) that bleaches clothes in a couple weeks and destroys plastics. Garbage bags, tarps, shopping bags become brittle and fly apart at a touch. So do milk jugs, so it depends on where you are...but you don't want to clean up fragmented denatured plastic.

I use milk jugs a lot. Sun damage gets them eventually but it takes awhile here.

Mike Haasl wrote:I've seen that done.  I think the smaller containers give the benefit (or disadvantage) of shorter thermal cycles.  While a 55 gallon drum may average out temps for a few days, a 1 gallon jug may do it for hours.  So they probably wouldn't get you through two cold days in a row but they should help on every cold night.  

Where I've seen them used, they were painted black.  I'm not sure if the paint protected them from UV degradation but it likely helped them collect more heat.

I could probably fill them all, get them on the back wall and then spray the entire thing black. I think I'm going to try it!

I have a waterwall made of these. Taking into account that there are other temperature control systems built in, when I put the waterwall up the average difference between inside and outside went up (from about 8 degrees to about 10, 2017 numbers). The temperature remains relatively stable even after weeks of cold, dropping slowly.

I also have two blue 55 gallon barrels which went in summer of 2018 and they appeared to have about the same result--1-2 degrees difference. On warmer days the difference between inside and outside is smaller (yesterday morning it was 33 outside and 46 inside, for a difference of 13 degrees).

I have about 150 water bottles, including the waterwall on the back and sides as well as water around the base on the support boards. I did not paint them.

They do deteriorate over time, but since we're still drinking milk I just replace them. The biggest problem is rupturing because of a freeze.

Summer temperatures are another issue. During the summer you want the temperatures inside to go down, so if that's your goal I definitely would not paint them black.

During the summer and late spring/early fall the temperatures inside with both doors closed range around 4-8 degrees above the outside (night--doors are open all day). I think part of this is because the greenhouse is built into a hill. With one door open it ranges around 2-6 degrees above outside. With both doors open, -2 to 2.

Since I never had the greenhouse during the summer without the waterwall, I can't say how that would be different.

Hi Elle,

I keep 200 gallons of water in my 26 ft high tunnel.  In my case I am using 3 gal plastic jugs.  My neighbor has been saving them for me for years.  Over time, they add up.

If you are using the jugs for heat retention you could cover them with black plastic maybe.  A black color would collect heat better anyways.  As for whether it would be enough to make a difference, it is going to come down to overall gallons/total thermal mass.

I have used milk jug plastic outside in the direct light for three years without issues, if you didn't mind replacing every three or four years you could go that route as well.  

I use milk jugs for quite a few things, makeshift cold frame/frost protection...   I have a 16 foot floating wooden dock that is three wooden boxes filled with milk jugs for flotation, that has been out there floating in the pond for half a decade now.  Milk jugs are pretty useful and last a fair little while before degrading.

John F Dean wrote:Hi Elle,

I keep 200 gallons of water in my 26 ft high tunnel.  In my case I am using 3 gal plastic jugs.  My neighbor has been saving them for me for years.  Over time, they add up.

I'd love to see a picture!!

My experience has been that clear plastic degrades quickly.  Solid plastic seems to last much longer.