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01/02/2014 at 22:47

The final top 2" layer of sand was then completed:

and depth checked:

Finally, this is it with 8 seed trays in position.  Each one is effectively a propagator in it's own right so that it's lid can be removed when seeds show signs of germination, without affecting any of the other trays.  To the right you can see the thermostat - this is a fancy one I already had and the probe is on a cable so can be placed inside a seed tray rather than in the sand if I wish.  However, it is really an overkill and the standard Parasene thermostat would be fine:

I've set the thermostat to 25C as a test tonight and will check in the morning.  I filled one seed tray with compost and put my max-min thermometer on top before covering with the lid.  That should give me a good idea of how warm the compost in the trays will actually reach when the sand is at 25C.  Fingers crossed!

01/02/2014 at 22:59

Thanks Mike!  If everything goes to plan the living room windowsill will be free of seed trays this spring for the first time ever, which I'm sure will please my other half!

01/02/2014 at 23:01

Nice one Bob

02/02/2014 at 21:45

Bugger I've bought 12 m of cable for a hot bed of 100cm x 80 cm


02/02/2014 at 22:04

Hi Clueless,  thanks for posting that as I just realised I made a mistake in the text above - I actually used a 12m cable, NOT a 6m one!

As long as you can fit that 12m of cable into your 100cm x 80cm hot bed without any of the cable touching itself, you will be fine as long as you do use a thermostat.  It will have the advantage of heating up quicker but won't use any more electricity as the thermostat will turn it off as soon as the sand reaches the set temperature.


02/02/2014 at 22:07

yes I have a matching thermostat


02/02/2014 at 22:09

Looks great - very professional! At 100kg very permanent too, how do you intend to use it after germination in spring?

02/02/2014 at 22:16

Daintiness you can add compost to all of the bed say (two inches)and use it to strike cuttings esp Dahlias


02/02/2014 at 22:18

brum all four inches of the sand or just the top inch or two ??


02/02/2014 at 22:19

Hi Daintiness, I have made a lid using the same exterior grade plywood as the base so once I don't need the heat any longer it will be turned off, the lid fitted and it'll become just a normal bench (which I'll be growing peppers on, as it happens!)

02/02/2014 at 22:36

Bob, Didn't think it possible, but I am now even more impressed...great planning! 

02/02/2014 at 22:49

Thanks Daintiness!   I find gardening is really all about planning - at the very least it gives us something interesting to do in the winter or while it's raining!

02/02/2014 at 22:59

and don't forget the wind


03/02/2014 at 09:01

HIYA Bob, nice one ,forward planning as well , hot bed ,propagater and a work bench ,we,ll be seeing you in the Dragons den soon, thanks for the pics and info really good,and soon as i can im wanting one of them for all my planned cuttings, cheers Bob 

03/02/2014 at 09:04

waiting for you heating results with bated breath Bob


03/02/2014 at 19:00

Hi all, the temperature results are in.  I left it a couple of days to make sure things had settled down.

With the probe placed in the sand and showing 25C, the temperature on the surface of a tray of compost placed on top of the sand and covered with a clear lid varied over a night and a day from between 15.5C to 19.5C (measured using a mix-min thermometer placed on top of the compost.)  Clearly, the air temperature in the shed has a fair effect on the compost temperature even though the sand is absolutely constant at 25C, so tonight I'm raising the sand temperature to 30C and will report back tomorrow.

Because I have a moveable thermostat probe, in order to keep an exact temperature in the seed trays themselves, I do have the option of putting the probe in the actual seed tray rather than in the sand below and will try that tomorrow night.


03/02/2014 at 19:34

 I made mine with sturdy plastic trays my local butcher kindly gave me he used them for carrying pies etc,, will last forever,,,,  

06/02/2014 at 19:05

Could you show the propagator with the lid on?  Was it easy enough to do?

06/02/2014 at 19:45

Hi David, I'll take a photo at the weekend.  I found it pretty easy to make - if you're reasonably good at DIY it would be a breeze.

08/02/2014 at 13:16




Hi David, as promised, here are photos of the lid.

The underside has a couple of battens to locate it properly and stop it sliding off:

Lid in place:

I also discovered that the cheap (£3.50 from Wilko) windowsill propagators fit perfectly - more by luck than judgement though! :

The small module trays in those are ideal for small batches of seeds, so I'll definitely be using them this way for my toms, peppers etc.

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