Topic: Soil warming cable/propogator

[Steve.]

After much thought over the last year I have taken the plunge and bought a soil warming cable and thermostat, to make a big propogating bench out in the greenhouse. I've worked out how I'm going to put it all together after much googling and discussion elsewhere on the net, but one question remains unanswered.

Does the sand the cable is in, need to be kept moist and is this especially important around the actual cable itself, if so...why?

Many thanks!

Steve...:)

[goodlife]

No it doesn't have to be kept moist..BUT..by doing so heat will distribute better and more evenly throughout the sand. With dry sand the cable is not as effective.

[Steve.]

Many thanks Goodlife

Steve...:)

[Tee Gee]

I prefer to keep the sand moist but found that this can be a bit of a problem when the hotbed is covered with trays.

To overcome this I give the sand a good soaking at the start of the growing season then cover it with a sheet of polythene.

I find the polythene keeps the moisture from evaporating, i.e. condensates form on the bottom of it so the surface of the sand is always quite moist, which as goodlife says; it distributes the heat better.

I find I can get a whole growing season from one soaking by using this method.

The other thing it does is keep the sand clean, i.e, free from soil/compost that seeps out of the trays/pots so I do not have to replace the sand each year.

This is how I do it;
http://www.thegardenersalmanac.co.uk/Data/Greenhouse%20heating/Greenhouse%20Heating.htm

[Steve.]

Many thanks TeeGee, that fully answers my question.

Steve..:)

[Two Choices]

I do pretty much the same as TG insofar as I water once at the start of the season and cover it with black polythene. I add some jeyes fluid to the water and this helps prevent mould growth.
I built my heated bed on the lower level of my greenhouse staging and then I use bubble wrap to build a sub-greenhouse (6ftx2ftx2ft) which houses the tomatoes and other plants in a heated environment until they are nearly two foot tall (ie the distance to the top of the staging).
Hope this helps TC

[Tee Gee]

I add some jeyes fluid to the water and this helps prevent mould growth.

I like that idea might try it!

Does it pong a bit once the heat is applied?

[Two Choices]

Can't say as I notice it too much TG as I do it at the same time as I wash down the inside with with Jeyes and leave it all open for a day or so tom 'blow through'. TC

[Hector]

I prefer to keep the sand moist...

To overcome this I give the sand a good soaking at the start of the growing season then cover it with a sheet of polythene.

I find the polythene keeps the moisture from evaporating, i.e. condensates form on the bottom of it so the surface of the sand is always quite moist, which as goodlife says; it distributes the heat better.


This is how I do it;
http://www.thegardenersalmanac.co.uk/Data/Greenhouse%20heating/Greenhouse%20Heating.htm

Do you think this would work as well with Hortag ( as I already have some of that)
Thanks for this. I have an ancient and huge propagator and wondered why I wasn't getting temp needed. I now realise substrate is dry as I have pre watered pots not the substrate

[daveyboi]

It is the moisture which distributes the heat through the medium otherwise  if the medium is dry it acts an insulator around the cable.

 

[ACE]

I don't know what materials you are using for the construction of the tray. I used some expanded foam sheets, the stuff they put in between the cavity walls when building nowadays. Just ask at any  building site for some offcuts You can glue, cut, saw and peg it all together. A wooden frame on the top covered in bubble wrap and Roberts your mother's brother.  It cuts down on running costs as it insulates very well and the heater hardly ever has to turn on. When I had the big poly tunnel we made a couple of 8' x 4' with just a couple of metres of heating cable in each. All the plants for our show gardens started life in these very warm propagators .

A bit large for a usual gardener, but for every 20 plants we grew 15 to 18 were rejected and as we usually needed 100 to 150 plants per square metre on a 10m x 15m show garden you can work out how many plants these propagators used to knock out.

[Hector]

It is the moisture which distributes the heat through the medium otherwise  if the medium is dry it acts an insulator around the cable.

You are a star.

[daveyboi]

It is the moisture which distributes the heat through the medium otherwise  if the medium is dry it acts an insulator around the cable.

You are a star.

I blush but thank you