Hints, Tips, and How Tos

Can Milk Jugs Help Grow Tomatoes?

The heat in the milk jugs is slowly released throughout the night

Well, I’m trying something new in my greenhouse this year – milk jugs. Yup, milk jugs. Here’s the theory… All along my row of tomato plants are old milk jugs full of water. All day long the sun warms up the water in those jugs. According to science, water holds heat better than air. So when it gets cool at night, the air in my greenhouse will cool off much quicker than the water in the milk jugs. Thus, the heat in the milk jugs will slowly release through the night – heating the air around them. That means my tomatoes stay warmer longer. It’s kinda like a heat battery for greenhouses. The more milk jugs of water, the more heat is saved up all day and released all night.

So does it work? Well, I can’t really say yet. When I did my first thermometer test, the temperature on the ground six inches from the a milk jug was 0.6 degrees warmer than the temperature at knee height three feet away. So if warm air rises, the knee height should have been warmer. Tonight I’m going to take a another temperature test – one near and one away from the jugs – this time both at knee height. I’ll try to keep you posted.

I still need to seal up my greenhouse a little better so the warm air has a harder time sneaking out at night, so it’s hard to say if the milk jugs are really doing much good. But I’m pretty sure they aren’t hurting anything – at least my tomatoes aren’t complaining…. Take  a look!

Tomato Clusters

Nice, huh? Here’s another shot…

Heat Batteries

Has anyone else tried something like this? How has it worked?

Update September 28: Last night the temperature dropped to -4.7° C. Inside the greenhouse on the far side away from the jugs the temperature dropped to 0.2° C. But near the milk jugs the temperature got no lower than 2.3° C. So, I’m impressed.

4 replies on “Can Milk Jugs Help Grow Tomatoes?”

I’ll post some pictures after we move in, but the house that we just bought has a green house with this kind of heating system. There are large steel drums filled with water under the germination bench on the back wall (northern wall) of the greenhouse. They are painted black to absorb more heat. The previous owner thought this worked quite well to maintain a warmer temperature at night.

Yes I would agree painting the jugs black would work better. You could also increase the heat capacityof your greenhouse by puting dark stone in areas where you can’t put water, like walkways. Also peat and rubber have pretty high heat capacities.

I like this idea… but I agree, black would absorb more heat during the day. When we camped in the desert of Mexico (yes, we seriously did this as crazy as it sounds), we used some kind of black bag for shower water which we filled each morning with water, left them in the sun, and then had warm water for a shower in the evening (we were doing construction work and very dirty). I don’t know if paint would actually work on the jugs, but maybe black garbage bags filled with water would work.

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