Market Farming

["Rob Wallbridge" <rob AT songberry.ca>]

Hi Alan,

I haven't encountered this myself, but my immediate response would be that
you need something to transmit and distribute the heat between your heat pad
and the trays, NOT something that insulates the trays from the heat -- if
anything, this may just make the problem worse, since the principle of
insulation is to slow transmission of heat, not spread it out. Apart from
using a sheet of copper or some such conducting metal, you'd actually
probably be further ahead by simply creating a single sealed air space
between the heat pad and the trays, although you'll lose some efficiency. In
the past I've used a heating cable to start seeds, and the recommendation
there is to bury it in an inch of wet sand - I never noticed "hot spots"
with this method, so that may be your best option.

Hope this helps,
Rob

Rob Wallbridge
Songberry Organic Farm
24 Sixth Line, Bristol, QC J0X 1G0
rob AT songberry.ca
www.songberry.ca
facebook: "Songberry Organic Farm"
twitter: @songberryfarm 


-----Original Message-----
From: market-farming-bounces AT lists.ibiblio.org
[mailto:market-farming-bounces AT lists.ibiblio.org] On Behalf Of Allan
Balliett
Sent: Tuesday, December 20, 2011 10:33 AM
To: Market Farming
Subject: Re: [Market-farming] Heating seedling trays

Here's a question:

I'm using one of those 'plastic film' heating mats, probably 2x4 ft.

I'm having trouble with 'hot spots' in it. I have a good thermostat,
which I set of 70degrees. I have umpteen small soil thermometers stuck
in the trays but, of course, the thermostat sensor can only be in one
spot, so, until it reads 70 there, it keeps the juice on throughout
the mat. (I've read up to 100degrees in the soil at one point. Weird,
100 degrees BAKES seeds, which doesn't seem right) Anyway, I've
decided to sandwich the heat mat between a 1inch thick sheet of rigid
insulation (which I've had there all along) and a half inch thick
sheet of sheathing rigid (foam) insulation in the hopes that the
temperature will even out across the board and the thermostat sensor
will pick up more accurately. My question is: have you ever tried a
heat mat sandwiched between insulation boards? Is there a danger of
over heating the heat pad while trying to get 70degrees through the
top insulation? Other than buy a new heat mat, how would you approach
this problem. (Yes, mostly working with wheatgrass, peas and
sunflowers)

Thanks

-Allan in WV



On Mon, Dec 19, 2011 at 8:35 AM, MAsteveINE <MAsteveINE AT 207me.com> wrote:
>
> The system you discribe is available from suppliers under several names
but
> commonly referred to as spaghetti tube, another alternative puts fin pipe
> (as is inside hot water baseboard) suspended under the bench. For a
> DIY system on the cheap use common black 1/2 inch plastic pipe in runs a
few
> inches apart; running warm water,
> with a Taco 007 pump, from some type of water heater. ( longer pump runs
of
> warm water is better than hot water which can overheat your crop, get your
> system together early and make a check run for a few days to see what is
> what; I like having the probe of an indoor/outdoor recording thermometer
> burried in the soil)
> My small system ran a Katz engine heater which is available at auto parts
> store; that was at the house (residence) where heat requirement was
minimal
>
> For late season we needed something for lots of  vine crops direct seeded
in
> 804 cell packs so we
>  put a 4' x 16' bench at about waist height, covered and skirted with 6
mil
> poly, a 1500 watt electric heater
> under there on a bulb type line voltage thermostat  Worked very well, and
> even better when we had
> the time and remembered to water with warm water!
>
> MAsteveINE
>
> 000000000000000000000000000000000000000000000000000000000000000000000000
>
> I’m looking for people’s experience heating seedling trays.  I’ve used
heat
> pads in the past but I saw a system recently on a farm near Olympia,
> Washington.  This system consisted of a hot water tank used to heat water
> which was circulated through small diameter tubes under seedling trays. 
The
> farmer indicated that it was a less expensive system to run than
resistance
> heat pads.  I’m wondering what the experience is of people on this site
and
> what their recommendations would be for efficiently heating seedling
trays.
> Any and all thoughts would be much appreciated.
>
>
>
> Regards,
>
> Roy
>
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