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Thread: warm roots

  1. #1
    Join Date
    Oct 2002
    Location
    Central Indiana
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    13

    warm roots

    I am in zone 5 and wont be heating my small greenhouse this winter,at least until March. I have some plants I would like to overwinter in there. I just don't want the roots to freeze.

    I picked up some pipe heating cables last spring on clearance and have been trying to figure out a way I could use them. They are 30' long and have a thermostat that kicks on at 38 degrees F. and is supposed to shut off when the pipe is heated to 45 deg.

    Is there any way I could use these to keep my plants from freezing?

    I know I'm not supposed to use them in any way other than the purpose that they were intended.
    I had heard of people cutting these type of cables and using them to heat a row of aquariums, so I figured that someone must have found a way to use them in a greenhouse.

    http://image1ex.villagephotos.com/pu...asp?id_=876671
    Last edited by gardentoad; 10-22-2002 at 12:35 PM.

  2. #2
    Join Date
    Feb 2002
    Location
    Newport, RI/Richmond, RI
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    70
    When you say "cables," do you actually mean a single cable like an extension cord or a mat with wire running through it like a heating pad? Not knowing exactly what you are working with, I'm not sure I can give any suggestions. My 2 biggest concerns with using electric heating elements is the risk of shock and the risk of shorts in a damp environment. If it is truely just a single fully waterproof cable, you should just be able to bury it in some sand. Running it in a snake pattern, setting your plants in between the runs should work fine. You might have to play with the depth of the cables to get uniform heat. With such a narror range of heating, you also might want to consider getting some of that rigid insulation to put on top of the sand, with holes cut for the plants. If its a mat, I wouldn't recommend cutting it open, unless you know what you're doing. I personally don't have the knowhow to give advice on doing that. Another thing, if the cable is not fully 100% waterproof, it will short out. You may need to enclose it in something that is waterproof. Copper pipe or galvanized conduit would work really well and help distribute the heat. Most plastic tubing would also work well, but I would make sure of its heat rating. Usually, this is printed on the side of the tube itself, as well as on the spool. One final note, with heat, I would seriously consider going out once a day to water, if needed.

    Bill Gauch.

  3. #3
    Join Date
    Oct 2002
    Location
    Central Indiana
    Posts
    13
    It is a plastic coated cable like an extension cord. I am going to try and attach a scan of it. It looks waterproof to me.
    If I have the pots sitting on top of the sand would the roots stay warm up the sides, or would I need enough sand to bury the pots? I was thinking about running it between the pots but I was afraid the pots would melt. It says on the package to only use on plastic pipe that is constantly full of water. I have some copper waterline pipe or I could buy pvc pipe ,fill it and cap it off to attach the cable to.
    I'm not sure what you mean with the rigid insulation. Are you talking about the Styrofoam sheets?
    Right now I have the plants on the floor of my greenhouse sitting on pea gravel thats over a french drain.

    The house is double walled,well caulked and I buried 2" of Styrofoam insulation around the perimeter 24" deep so it is as insulated as I can get it. I can't see heating the whole house (9'X20 lean-to) when I only have about 30 plants in 1-3 gal. pots that I want to keep above freezing. I considered just using light bulbs to warm the area, but the heat would rise above the plants so I'd like to have the source under or at least near the bottom of the plants. I liked the cable idea because of the thermostat that would shut it off on sunny days so the plants wouldn't get warm enough to break dormancy. I plan to set my exhaust fan to kick on at 60 deg. F.

    http://image1ex.villagephotos.com/pu...asp?id_=876671
    Last edited by gardentoad; 10-22-2002 at 12:36 PM.

  4. #4
    Join Date
    Feb 2002
    Location
    Newport, RI/Richmond, RI
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    Well, that stuff looks pretty waterproof to me. Just make sure you don't let either end get wet. I have a question for you, which determines what the best approach to keeping these plants is. Are these plants hardy, not hardy in your area, or tropical. If they are tropical, just keeping the roots from freezing probably won't get them through the winter. If they are hardy, I would just let them go dormant. I would also cover the greenhouse with white plastic to moderate the temps. I would probably do the same thing if the plants were almost hardy or marginally hardy. Finally, if the cable gets hot enough to melt plastic, I would be supprised. Most plastics start to get soft at 150 F or higher. Most don't become fully melted until 200-300 F. Finally, if you only want to heat part of the house, you could make a "wall" out of just about anything. If you can shrink the size down to 9x4, it would be a lot more economical to heat. Actually, a 5x4 would be even better, but I'm not sure about the total area that your plants take up. If you sectioned off this area in the center of the house, you could even shrink the height down and use the rest of the house as a thermal insulator. Finally, in your situation, look at the specs for the cable. If it doesn't get hotter than about 80-90 F, I would just run it in a snake pattern and set the pots right on it. Try to keep the pots as close together as possible to make a sort-of thermal mass. Oh yeah, the insulation I was talking about is the rigid styrofoam stuff. You could make some sort of box out of it just to retain the heat in the root zone. If you leave a hole around every plant for watering, that should work quite well.

    Bill Gauch.

  5. #5
    Join Date
    Oct 2002
    Location
    Central Indiana
    Posts
    13
    Thank you for the fast and informative reply.
    I hadn't thought about closing a section of the house off. I could drape plastic over a bench to tent the plants on the floor under it or section a space from ceiling to floor. If I do that, would I need the exhaust fan to be part of it(west wall) or have an opening in the top to keep it from overheating? I am overwintering plant that are hardy to zone 6-7, I'm in zone 5, and some trees & bushes that are hardy here but only 6-8" tall so I want to protect them this first year. I want to keep them dormant, just not frozen in the pot. The temps outside can reach 20 below and I have an open field to the west of the house so the wind really picks up some speed. This being a Leanto, the warmest place would be against the north wall. It is against an unheated garage. I would loose some light here, but I wouldn't need it with the plants being dormant, right? I have the plants on the floor now because I think the temperature fluctuates less there, but they are against the south outside wall.

    I have lots of tropicals that I bring in every year that get so scraggly but I can't afford to heat the house enough for them. I decided to insulate the house to the max while I'm young enough to do it and have it ready to use all winter when my children are grown.

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