Garden Tunnels.

[Gary350]

Is there any information online with data about how warm tunnels get during the day in cold weather?

I have a roll of white color plastic, I think it is 6 or 8 ft wide and maybe 30 ft long. Trial & error is a lot of work to build and test to learn if it is too hot or too cold. ???

I have a 120 volt 8700 Lumen LED grow light that has never been used.

Mother Earth News says, 200 btu of heat per square foot in winter when sun is low in the sky. Only when sun is perpendicular to the plastic you get 200 BTU. I need a temperature rise of 25 degrees during the day. How is BTU converted to heat rise in degrees F? I don't know correct search word to find info on btu to temperature.

Alt codes stopped working on my computer I don't dare to try alt code it deletes everything and closes every thing.

[applestar]

You are going to get a wide range of temperatures depending on

1. how you build the tunnel
* how you secure the ends
* bury all side edges or leave on surface and use ground pins or bricks etc to hold down
* secure to end hoops
* caterpillar tie-down with cord to prevent proofing/flapping

2. type of material
* light transmission
* thickness and coating
* vented or unvented and type (holes or slits, top or sides)

3. with or without additional layers
* multi layer example — innermost insect mesh layer acts as windbreak in winter as well as excluding pests + vented plastic + floating cover for maximum warmth and prevent radiated heat loss at night + bird netting or cord tie down to protect from wind gusts

Overheating in winter can be the worst for the plants, so daily raising sides or opening vents becomes necessary if solid plastic is used.

Another innovative method is to use two narrower lengths that overlap at the top, which allows excess heat to escape and provides easier venting and access (pull apart at top to open, pull back together to close) — but this definitely needs cross-cross, corded tie down or other methods (if you have extra hoops, you could secure with extra hoops on the outside) keep closed and to hold in place in windy locations.

[imafan26]

I would never need to do this for warmth, but I know some tunnels have a double layer of plastic with air between them to add warmth.

[digitS']

Protective growing for the gardener certainly comes down to Trial and, vigorous attention to weather and temperatures, so as to avoid Error.

For a few months every Spring, I use a simple and temporary tunnel covering 9' by 20' of my backyard garden. Also, 1 or more "hoopies" are set up on my lawn to protect flats of plant starts during their hardening-off time before transplanting to the open garden. That would make good use of the piece of plastic film.

The plants in the photo are even younger than hardening-off stage. It is very likely that I was moving them back into the greenhouse every night. There is little difference between outdoor temperatures and temperature under a single sheet of plastic during hours of darkness. A tarp over the little structure can make a difference.

During hours of sunlight, a great deal of attention is required.

Steve

[digitS']

Looking at the greenhouse temperature 2 hours after sunrise this morning made me think of this thread. My greenhouse is essentially a sunshed with a clear plastic film on the south wall nearly to soil level, an insulated north wall, partial insulated east and west walls (with door and exhaust fan), and an insulated roof. I run no heat in there at this time of year.

Yesterday, there were no sunbreaks with clouds all day. It is 37°f (3°C) with continuing cloudiness and almost no air movement. The greenhouse is 38° (what's that, still 3°C).

Okay, that's 2 hours of light but the sun cannot be seen. Looking at something that I wrote down regarding that tunnel pictured above on a Spring day several years ago: It had been a sunny day the day before and 60° (16°C). The tunnel fell just below 40° (4C) by morning with 27f (-3C)outdoors and quickly warmed. I had trouble keeping it below 80° (27C) through that day. It was okay with me for it to be that warm in there but I was nearly to placing a fan in there to keep the temperature from climbing much higher. That's something that I will do on a few sunny Spring days every year even with the window there at the far end and the door will be completely open.

Structure size, sunlight, wind, and sunlight all make a difference. But, even the simplest structure for protective growing can make a positive difference to an early start.

Steve

[imafan26]

If you do have tunnels for heat, you do have to monitor the temperature a lot more. Applestar's remote temp set up could be really useful. You would have to open and close the tunnels to moderate the temperature.

For me heat build up is a problem. The first time I tried row covers, everything cooked, because even the light row cover trapped too much heat. I would never use a totally plastic tunnel because it would be a sauna. At most I can only use partial plastic on the top as a rain cover. Some people here do use tarps in summer to block lite to keep plants from burning in a shade house. It is easier to get a tarp than to find shade cloth for the garden. The garden centers only sell 90% shade cloth mainly for patio covers. These are too dark to be useful to cover shade houses.

The botanical garden put in a large glass conservatory years ago at the time a few of us asked why? Glass houses are designed to keep in heat. The conservatory is being used for display, but they have tarped the entire roof to block most of the light and the side vents and doors are always open. What is displayed in the conservatory are potted plants when they are in bloom. 3/4 of the conservatory is used for the display, the last quarter is used for storage which they needed more of. The bugs can still get in too.

The old display area next to the orchid collection is still sometimes used.