Making a hotbed

[roiphil]

Ok got my base 3 ft x 4 ft approx and frame about 2 foot high and enclosed the frame in bubble wrap, for the base i put in 1 inch deep gravel with 1 inch deep sand on top of gravel, then i lay my soil warming cable and cover with 2 inches sand, technical question, i am using a thermostat that has a heat sensor cable of about 3 foot long with the sensor on the end do i put this in the sand with the soil warming cable or do i hang it inside hot bed enclosure, do i want the thermostat to control sand temp or air temp, i have also installed 2 water misters which i can have come on, on a timer, and what would be a general good temperature to aim for in the hotbed for cuttings and seeds

Phil

[ideasguy]

RE:

do i want the thermostat to control sand temp or air temp

You should put the sensor into the sand, Phil.

As I recall, you should keep the sand moist, but not like a swamp of course.
The soil heater then warms the moist sand and creates a better environment.
Comment from others, particularly in relation to temperature, would be appreciated.
I imagine it depends entirely on what you are intending to put in the frame.

[roiphil]

think you could be right their george, the hotbed will be for cuttings hence the misting system on timer to mist on the hour for so many minutes, will also use it for seeds, i know you have to keep sand moist, on a normal hotbed thermostat has a rod that you bury in the sand so my one should work on the same principle, (to tight to buy a proper one so i am using one that i have left over from when i kept lizards years ago) waste not want not it still controls temperature, even used it on a home made chicken incubator to make the heating come on and off when needed 

could do with some advise on a temperature to aim for

Phil

[newplantguy]

I have used heated mist beds for many years.
Propagation has always been an interest of mine and was a big part of my job for many years.
The sensor cable goes in the sand, you can also put it into the trays you stand on the heated bed if you are using it this way.
The sand needs to be kept moist.
The temperature to aim for is around 21 centigrade in the sand or say 15  to 18 centigrade in the trays if you are using these on the bed.
You can use lower temperatures to save energy 18 centigrade in the sand gives around 12 to 15 in the trays
If you need lower temperature then you can adjust as required on the thermostat. 
I also cover bed with polythene instead of using mist. You need shading though or white polythene in summer.
I have also used mist and polythene combinded.
Paul.

[roiphil]

thanks for that paul will take a piccy later, thinking i will put the sensor in the sand even though cutting and seeds will be in trays

[roiphil]

And the hot bed is finished, wooden frame bubble wrap on the inside and outside



The thermostat is an old one that i had kicking around from a home made incubator, notice the reminder on it for the temp 


plastic fixed to wooden base then inch of gravel inch on sand then the soil warming cable then 2 inches of sand, the temp gauge for the thermostate is in the sand aswell


even have two misters in it one back corner other opposite front corner




Edited by Global Moderator - Gold Star awarded to Phil for this achievment -

[NightHawk]

You've saved yourself an awful lot of money there Phil, being able to construct all that.

I bet you couldn't get one that size for the cost of materials you had to use.  I don't know if they even come in that size anyway. 

Of course you've now made yourself the expert on hot-bed design for any of our other members. 

Take a bow and accept one of my Gold Stars for your great achievement. 

Laurie.

[roiphil]

Thank you another gold star to my collection  i think the dearest part was the actual soil warming cable at about 60 euro and i got it from a garden centre in the UK as it was about 10 euro cheaper than buying one over here, even with the postage on top, in total it probably cost about 100 - 120 euro which is not to bad had most bits had to buy the 2x1 for the frame and the bubble wrap had sand, misters, pipework, etc, probably a bit high but i wanted to be able to get my head in it without bending over to far due to the old back 

[newplantguy]

Well done Phil, I'm jealous looks the business
Well worth a gold star.
Paul

[roiphil]

Thank you everyone i just hope it all works when the time comes, i have to keep on reminding myself that your basically warming the sand not the all the air inside  , it should work may have to add some shading if need be, the greenhouse roof has got shading as i found the corrugated plastic sheets caused the greenhouse to get like a sauna on hot days, so i got some windbreak material and stapled it to the roof beams and problem solved