Soil warming cable - Propogator

Discussion in 'Propagation This Month' started by Steve R, Dec 3, 2011.

  1. Steve R

    Steve R Soil Furtler

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    I've toyed with this idea before but never got round to fixing it up.

    I want to make a propogator in my greenhouse with a timber frame, soil warming cable and thermostat.

    [​IMG]

    Does anyone here use/own a similar setup and can offer any advice, pro's and con's for it.

    I've read quite a bit online about making them but I would like to know what sort of temperature ranges can be achieved, and to achieve those temps..how far apart the cable needs to be (then I can work out how much cable to buy).

    Here's a quote that seems to be in most places online about temps...

    "Assuming that the cables are laid between 3 & 4 inches apart you will be able to increase the soil temperature by 20ºF to 25 ºF. You may run the cables as close together as 2 inches in order to achieve higher temperatures."

    Can anyone expand on this quote with pratical knowledge rather than sales bummf? And...anything else I should know?

    Steve...:)
     
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    • Lolimac

      Lolimac Guest

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      Go for it Steve:thumbsup: Mr Lolimac made one for me in my GH...it's great..On the top of it we put those large plastic cloches on as lids.He Made it with sturdy timber as it is very heavy....
      I'm sorry i can't give you any technical advice but i can advise to keep it damp otherwise it forms a crust....
      Will take photo and ask 'sleeping beauty' when he gets up....
       
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      • Scrungee

        Scrungee Well known for it

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        Steve, what's the best price you've found these going for?

        I was up late last night looking at the cost of thermostatically controlled propagators, in the early hours when I couldn't sleep I started looking at heat mats + thermostats, but I started looking at these cables I'd managed to tire myself out enough to get some sleep.

        The cheapest I found was that Parasene one in your pic, a 6m/20 foot one for £24.50 + a thermostat from the same seller also £24.50, plus £3.35 P&P making it cheaper than a thermostatic propagator that would only take 2 seed trays. I also have half a dozen perspex propagator covers and about 30 seed trays they fit. This might be the one for me.
         
      • miraflores

        miraflores Total Gardener

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        I think it will work but let us know.
         
      • shiney

        shiney President, Grumpy Old Men's Club Staff Member

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        Yippee!!! For once I am able to give some technical advice as I am usually the worst DIY person you could meet :heehee:

        I built my propagator in that fashion in 1976 and it's still working perfectly :dbgrtmb:. I think it's worth getting more cable than they suggest and run it closer. The initial outlay is more, shouldn't be too much, but the running cost won't be any higher if it's thermostatically controlled. In those days we didn't have much choice on length and the one I got allowed me to have them 2" apart. Make sure you don't have any cable too near the thermostat - which I presume would be of the probe type.

        I had asked a number of people about the best way to make it and ended up with what they concluded was the best way. Although I did cut corners to reduce cost.

        I used 9" wide chipboard shelving because I couldn't afford to pay for good timber and lined the inside with plastic. 9" may sound a bit much but the deeper you can make the bed the more even the temperature and the more accurate the control. I put in 3" of sand, laid the cable on top and then another 1" of sand to bed it in. Over that I put 2+" of gravel.
        My propagator is 5' + 3' and is big and very heavy, so I put extra supports under the bench it's on.

        To conserve energy you would also need to have some sort of cover (we haven't had a cover for many years because that is where Oscar had set up home). Mine was a 'Heath Robinson' type that I cobbled together. I put 3' high 1" x 1" batons standing upright in the corners and half way down the sides. In the top of each baton I put a galvanised 'felt roofing nail' and then ran wire around each nail and from nail to nail. This formed a framework of wire at the top of the batons. Don't run too much wire or it may make it harder for you to put things in the propagator.

        I then laid clear plastic sheeting over the top of the wire and down the sides and used drawing pins to pin it to the batons at the back. The rest of it I left unpinned. When I needed access I just rolled it back over the top of the wires. Sometimes some of the plants needed more heat/humidity than others so I could lift part of the plastic to give some ventilation. In the sunny weather it was OK to roll it back because the ambient temperature in the greenhouse got quite high so it turned the thermostat off.

        The plastic lasted about three years before I changed it. Depending on the type of plastic (usually very cheep) it would eventually start going opaque or brittle.

        now that Oscar is, sadly, no longer with us I have put plastic garden cloches over it. Not the solid plastic but the 5' x 2' thin plastic sheet on wire hoops that I bought for £1 in the Pound Shop. The wire hoops are just pushed into the sand/gravel and I lift one end out each time to do the watering.

        I've always had very even temperatures but found that I, mentally, recalibrated the thermostat. A small thermometer for the propagator will allow you to check it.

        Oscar had his own way of adjusting the temperature :heehee:. He could turn it down by sleeping on the area above the thermostat probe :DOH:.

        Any other questions - I shall attempt to answer :D
         
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        • Steve R

          Steve R Soil Furtler

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          Shiney, that's an invaluable post...many, many thanks!

          Scrungee, I've not looked too closely at price at the moment, but it was for the same reason that I was looking at the cable and thermostat...ready made propogators are too expensive for the useable space they have, in comparison.

          Steve...:)
           
        • shiney

          shiney President, Grumpy Old Men's Club Staff Member

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          Hi loli,
          If you use gravel on the top it doesn't form a crust :dbgrtmb:.

          Also, the gravel can be lifted off and washed every so often. It's surprising how often the plants in there have dropped seeds and produced new plants :thumbsup: (we keep some more tender, adult, plants in there in the winter) - but we also seem to get weeds growing in it as well :(.
           
        • davygfuchsia

          davygfuchsia Gardener

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          Hi Steve
          Shiney has said most of the basics ..
          I have had a hotbed for over 20yrs and still have the same cable ,and this autumn needed to replaced the rod type thermostat. I have a 2 inch thick sheet of polystyrene on the base of mine then the cables sandwiched between 2in of sand .As shiney says it crusts up when dry ,I used to just keep it wet but a couple of years ago I put some capillary matting on it which I keep wet much easier ...Mine is across the back of my glasshouse so is 8ft x 3ft.
          I don't cover mine , I use it to stand more tender plants on over winter, and root cuttings in standard trays with the plastic dome lids .. and germinate seeds .. A great asset for the serious grower ..

          Dave
          Definatly a must item ...
           
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          • Lolimac

            Lolimac Guest

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            Thanks Shiney,never thought of putting gravel on top:dbgrtmb:
             
          • shiney

            shiney President, Grumpy Old Men's Club Staff Member

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            Hi Dave,
            Yes, most of the time I don't cover ours but I do for some of the propagating and to protect some of the very tender plants (we shouldn't really have any very tender plants but we do these things :))

            We used to use capillary matting but found that we got algae growing on it, weeds in it and some of the roots of the plants getting into it. As we didn't spend as much time looking after things, as we should, it then became awkward trying to keep the matting clean and undamaged. With the gravel, roots don't get clogged in it, weeds come out easily and a quick scooping out of the gravel and washing every couple of years or so only takes 15 minutes :thumbsup:

            We don't keep it damp as we water the plants regularly but if we are going away and friends are looking after the greenhouse we then make it damp before we go.

            We never seem to find the time to do things properly :( :heehee:
             
          • Scrungee

            Scrungee Well known for it

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            That sounds rather heavy for my staging, you must have about 10 x 20kg bags of sand in there.


            My staging could cope with that. From Parasene's pic of their thermostat, the edge board is about twice the depth of a seed tray, so the fill depth must be around 3"/75mm:

            [​IMG]


            I've checked in my greenhouse and I've got 10 of these Sankey propagator tops and 30+ (yet another Wilkos bargain many years ago) of the seed trays they fit, so can I assume these could sit on top of the gravel bed with the need for a further cover?

            [​IMG]


            Those Sankey seed trays measure 240mm wide x 380mm long, and as my staging is 470mm wide I'm looking at constructing something approx. 1500 x 450mm internally containing 6 trays (long edges parallel).

            Is it essential to construct a timber edged tray? I wondered if a large plastic tray could be used, something like either the Garland Metre Square Tray (1000 x 1000 x 120mm deep). It would lose some heat from the edges but would be much easier to clean, although it would cost around £25 (but the bottom cut off and old plastic cold water storage tank from a skip would cost nothing).
             
          • Steve R

            Steve R Soil Furtler

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            I think you have said it yourself Scrungee, you would lose some heat from the edges. But I guess if your wanting to lighten the load so to speak and use a plastic tray with Polystyrene base...then there would be no reason I could see why you cant use the ploystyrene up the edges to retain the heat there too.

            Shiney and Davyg, as you have both done your diferently (one heavy, the other lighter), I dont suppose you could post photo's of the stand you have these hotbeds on? Just so I can get an idea of how big the construction will need to be here for me.

            Steve...:)
             
          • shiney

            shiney President, Grumpy Old Men's Club Staff Member

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            Steve, Will do, but going shopping now.

            You'll need to remember that mine is 35 years old :rolleyespink: :dbgrtmb:
             
          • Steve R

            Steve R Soil Furtler

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            Yup, built to last is what I will want.:dbgrtmb:

            Steve...:)
             
          • shiney

            shiney President, Grumpy Old Men's Club Staff Member

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            I've not bothered to tidy up before taking the photos :o

            This first one is just a view towards the propagator. 5' x 3' x 9"

            [​IMG]

            [​IMG]

            The section of benching it's on is 6' x 3' and it has four supports (1.25" x 1.5") that came with it. Two in the front and two in the middle. The ends and back of the bench rest on a support that runs all round the greenhouse (part of the structure).

            I added two very hefty supports made from four 2" x 7" hardwood planks (from the local tip). Each support has an upright with a cross piece laid flat on top of it (cut to fit the exact height of the bench) and the cross pieces are bolted to to the existing supports. The one by the glass is bolted to the support running round the greenhouse (at the side and back) and to the front upright. The one the other end is bolted to the frame support of the benching that runs at right angles to it, the support running along the back of the greenhouse and the leg of the other bench.


            [​IMG]


            [​IMG]


            The gravel I have used is mixed sizes

            [​IMG]

            At the moment I'm keeping some of my chilli plants in there to save me having to bring them indoors.

            There are about seven different types (all from pretty hot to mouth busting :D) and the ones in the last photo below have a citrus flavour as well.

            [​IMG]

            [​IMG]

            [​IMG]

            [​IMG]
             
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