I’ve had the parts for ages but was goaded into building it 1) because the days are getting shorter and will soon be colder too, and 2) If Toby Buckland can do it in half an hour…. OK, it’s much bigger but it took me a whole day and I needed a hand here and there. I feel so inadequate… Anyway if you missed the expert sprint version on GW, here’s my slo-mo propagator.
First things first – my soil warming cable is a fixed length, but I could change the size of the frame, so I laid the cable out roughly first and then decided on a frame size to suit.
Then, take the cable away, put it somewhere safe and build a simple four sided box frame out of tongue and groove planks, or similar
A bit of a jump forward, but it’s only joinery. The four planks are joined together at the corners with posts which will form the uprights for the frame to support the bubble-wrap tent. The box is lined with polythene stuck down with gaffer tape.
Fix cross struts across the top of the posts to make the frame for the bubble wrap tent.
Lay sheet polystyrene in the base, lay the soil warming cable on top (which will fit perfectly of course!) and tape it down with gaffer tape to keep it in place. The soil warming cable is wired into a thermostat (black box on side. Just drill a hole in the wooden side about half way up and push the metal thermostat probe in. The cable and thermostat is plugged into a proper, pukka waterproof socket (yes, it’s wired back to an RCD in the potting shed)
Then cover the cable with sand to about 2″, making sure the thermostat probe is covered completely. Bubble wrap the back of the frame before filling with sand, because it’s impossible to move afterwards.
Cover the sand with weed control fabric and stick or staple gun it to the wooden base
and then add bubble wrap tent which folds over the front.
I’ll use it for speeding up rooting of cuttings, and when the temp drops it will be a higher temp area inside the greenhouse to overwinter the Colocasias and Cyperus papyrus.
Costings:
Wooden frame (from stored off cuts – hence odd painted bits)
Polythene (filched from father-in-law)
Polystyrene (recovered from tea room walls when renovated last year)
Soil warming cable £25.00
Thermostat £2.50 (bought from friend who bought three on Ebay)
Sand (left by builders who did the house)
Membrane fabric (happened to have it, but about £3.00 in garden centres
Bubble wrap (sort of filched it too….)
7 Responses to “How to build a heated propagation unit….”
That looks really good Sue and very sensibly explained too. Now I just need to make a bench big enough to fit a decent propagation unit before I make one too.
Fantastic. I'm planning a trip down from Aberdeen in a week or two. I'll try and make a detour to see the nursery.
Hi thank you that was very informative and I am now collecting all the items required.
Just one question.
You put the warming cables onto polystyrene do you have any problem with the polystyrene melting. I will be very interested if you could have a look at one corner to see if there is any effect on the polystirene.
This is because I am planning to do the same as yourself with reference to the building.
Billy
South Yorkshire
Hello Billy. No problem at all. The temperature of the cable is too low to melt polystyrene and the heat is disseminated through the sand. Best of luck. Sue
hi great idea i was wondering wha size your cable and table are please . i have a 6foot longtable and i was thinking of buying a 24 meter cable would that be TOO warm do you think
Hi again I have purchased a 24 meter cable and a thermostat both have plugs on so I presume the cable can be used as a stand alone without a thermostat . however as I wish to attach a thermostat, do I take the plug of the cable and feed the end of the cable through a hole, made in the wooden frame, and attach it to to the thermostat in the vacent hole ? the instruchions from parasene are dreadful
Hi BD. What I did was looped the heated cable from the thermostat over the edge of the wood frame. I didn't want to take the thermostat apart as it was already wired in. The first couple of feet of the cable is black and insulated before it leads into the heated section. I did drill a hole for the thermostat probe. As you've got them as separate items you will have to figure out how to wire them together.