I have just bought a large (22" x 15") Sankey 22 watt heated propagator for
£20. I put some cuttings in it and switched it on. With an ambient
temperature of 62F, a thermometer pushed to the bottom of the pot registers
a temperature of 98F, in the middle of the pot it is 85F and resting on top
it is 72F. I have compared the thermometer with another and am happy that
it is accurate. The propagator is placed on a sheet of polystyrene.

This sounds as though it could fry cuttings pushed in too deep. What
temperatures should I be using and at what measurement point. It has only
been on for 36 hours so far and nothing has died yet. Presumably this steep
gradient is normal, irrespective of the actual temperatures.

"peterlsutton" wrote in message
...
I have just bought a large (22" x 15") Sankey 22 watt heated propagator
for
£20. I put some cuttings in it and switched it on. With an ambient
temperature of 62F, a thermometer pushed to the bottom of the pot
registers
a temperature of 98F, in the middle of the pot it is 85F and resting on
top
it is 72F. I have compared the thermometer with another and am happy that
it is accurate. The propagator is placed on a sheet of polystyrene.

This sounds as though it could fry cuttings pushed in too deep. What
temperatures should I be using and at what measurement point. It has only
been on for 36 hours so far and nothing has died yet. Presumably this
steep
gradient is normal, irrespective of the actual temperatures.

As a general rule I use 21c at the bottom and cooler for the tops.
--
Charlie, gardening in Cornwall.
http://www.roselandhouse.co.uk
Holders of National Plant Collection of Clematis viticella (cvs)

On Mon, 18 Apr 2005 09:51:38 GMT, "peterlsutton"
wrote:

I have just bought a large (22" x 15") Sankey 22 watt heated propagator for
£20. I put some cuttings in it and switched it on. With an ambient
temperature of 62F, a thermometer pushed to the bottom of the pot registers
a temperature of 98F, in the middle of the pot it is 85F and resting on top
it is 72F. I have compared the thermometer with another and am happy that
it is accurate. The propagator is placed on a sheet of polystyrene.

This sounds as though it could fry cuttings pushed in too deep. What
temperatures should I be using and at what measurement point. It has only
been on for 36 hours so far and nothing has died yet. Presumably this steep
gradient is normal, irrespective of the actual temperatures.

Yes, and laterally as well - it's quite patchy. A lot will depend if
your rooting medium is in pots on sand or similar or if it's direct
into the propagator base. If the latter it will probably be on the
warm side if the cuttings are too deep. I use one of these for
germinating Cyclamen seeds for which I want a constant18C, I've hacked
a proper thermostat into the mains lead. By proper I mean reasonably
accurate (+/- 2C or better) and above all repeatable.Suitable
instruments are available on the electronic surplus market. This one
is OK.
http://www.highland-weather-shop.com...tat-Controller

I've had a couple of these from him, one runs my workshop heating with
the help of a suitably rated mains relay, the other controls a
propagator like yours. It's reassuring to know that what you see on
the display is what you get.

=================================================

Rod

Weed my email address to reply.
http://website.lineone.net/~rodcraddock/index.html

Hi Rod ,How have you got the controller wired to use with the propagator?I
have two of these controllers one is in use with a 2kw heater,I am not using
the other one .So you have got me thinking about using mine in conjunction
with my sankey propagator which has no thermostat.Are you powering (live)the
controller from the power to the propagator or have you got two separate
fused supplies.
Also how have you got the unit set up,have you got the parameters set ,so
say the propagator comes on when the temp drops to 17 then off at 19 to
maintain around 18 c.
I have found the unit a bit of a fiddle to wire and set up.If you are not
too good on the DIY then I would suggest to those who aren't to forget this
unit.The instructions are quite technical,I have found you have to really
mess about until you have got it right and understand how the unit is set.I
thought you could just set it at say 18c and that was it ,but it isn't as
simple as that,how have you found it?

--
Thanks Keith,Nottingham,England,UK.
"Rod" wrote in message
...
On Mon, 18 Apr 2005 09:51:38 GMT, "peterlsutton"
wrote:

I have just bought a large (22" x 15") Sankey 22 watt heated propagator
for
£20. I put some cuttings in it and switched it on. With an ambient
temperature of 62F, a thermometer pushed to the bottom of the pot
registers
a temperature of 98F, in the middle of the pot it is 85F and resting on
top
it is 72F. I have compared the thermometer with another and am happy
that
it is accurate. The propagator is placed on a sheet of polystyrene.

This sounds as though it could fry cuttings pushed in too deep. What
temperatures should I be using and at what measurement point. It has
only
been on for 36 hours so far and nothing has died yet. Presumably this
steep
gradient is normal, irrespective of the actual temperatures.

Yes, and laterally as well - it's quite patchy. A lot will depend if
your rooting medium is in pots on sand or similar or if it's direct
into the propagator base. If the latter it will probably be on the
warm side if the cuttings are too deep. I use one of these for
germinating Cyclamen seeds for which I want a constant18C, I've hacked
a proper thermostat into the mains lead. By proper I mean reasonably
accurate (+/- 2C or better) and above all repeatable.Suitable
instruments are available on the electronic surplus market. This one
is OK.

http://www.highland-weather-shop.com...tat-Controller

I've had a couple of these from him, one runs my workshop heating with
the help of a suitably rated mains relay, the other controls a
propagator like yours. It's reassuring to know that what you see on
the display is what you get.

=================================================

Rod

Weed my email address to reply.
http://website.lineone.net/~rodcraddock/index.html

"With an ambient temperature of 62F, a thermometer pushed to the bottom of
the pot registers a temperature of 98F, in the middle of the pot it is
85F and resting on top it is 72F. I have compared the thermometer with
another and am happy that
it is accurate.

As a general rule I use 21c at the bottom and cooler for the tops.
--
Charlie, gardening in Cornwall.
http://www.roselandhouse.co.uk
Holders of National Plant Collection of Clematis viticella (cvs)


Many thanks Charlie - I would be down there to see you except I am in
Yorkshire. I assume you mean a temperature of 21C at the bottom of the
cutting. That is way less than than the 85F (30C) I am getting. I am
surprised that Sankey can sell a unit that is so hot.

Peter

In message , peterlsutton
writes

Many thanks Charlie - I would be down there to see you except I am in
Yorkshire. I assume you mean a temperature of 21C at the bottom of the
cutting. That is way less than than the 85F (30C) I am getting. I am
surprised that Sankey can sell a unit that is so hot.

Maybe it is malfunctioning if you think it getting too hot?
--
Chris French and Helen Johnson, Leeds
urg Suppliers and References FAQ:
http://www.familyfrench.co.uk/garden/urgfaq/index.html

"Rod" wrote in message
...
On Mon, 18 Apr 2005 09:51:38 GMT, "peterlsutton"
wrote:


Yes, and laterally as well - it's quite patchy. A lot will depend if
your rooting medium is in pots on sand or similar or if it's direct
into the propagator base. If the latter it will probably be on the
warm side if the cuttings are too deep. I use one of these for
germinating Cyclamen seeds for which I want a constant18C, I've hacked
a proper thermostat into the mains lead. By proper I mean reasonably
accurate (+/- 2C or better) and above all repeatable.Suitable
instruments are available on the electronic surplus market. This one
is OK.

http://www.highland-weather-shop.com...rmostat-Contro
ller

I've had a couple of these from him, one runs my workshop heating with
the help of a suitably rated mains relay, the other controls a
propagator like yours. It's reassuring to know that what you see on
the display is what you get.

=================================================

Rod

Weed my email address to reply.
http://website.lineone.net/~rodcraddock/index.html

Many thanks Rod - that has been really useful. I have just ordered a
controller from that site. I couldn't find such an item with Google. I may
well build my own propagator, with an added light source. I know that a
couple of inches of sand in the propagator will even out lateral temperature
differances, but it eats into the height available, and is additional
insulation meaning more of the heat will go out sideways and downwards.
Would a metal sheet spread the heat more evenly without the insulation
effect.

Your cyclamen look fantastic, you must have got it right. Do different
types of say herbaceous perennials need different temperatures for seeds and
cuttings and where do you find this information, and what about the light
requirements?

Thanks again for your help

Peter

"Chris French and Helen Johnson" wrote
in message ...
In message , peterlsutton
writes

Many thanks Charlie - I would be down there to see you except I am in
Yorkshire. I assume you mean a temperature of 21C at the bottom of the
cutting. That is way less than than the 85F (30C) I am getting. I am
surprised that Sankey can sell a unit that is so hot.

Maybe it is malfunctioning if you think it getting too hot?
--
Chris French and Helen Johnson, Leeds
urg Suppliers and References FAQ:
http://www.familyfrench.co.uk/garden/urgfaq/index.html

This had passed through my mind - but it is so basis that there is nothing
to malfunction. There is no controller. 240 volts goes in and heats a pad.
The only way the pad could malfunction is if it shorted in which case there
would be less heat or no heat. The only alternative is that the wrong pad
has been used, but after googling they appear to be pretty standard at 10 to
15 watts per square foot. At least if I plant some plum stones I should get
stewed prunes.

I think that the basic problem is that in a propagator the bottom of a pot
can be 30F higher than the top of the pot, and this is going to happen in
any propagator. And anyone who only measures the surface temperature will
be unaware of this gradient.

Peter

On Tue, 19 Apr 2005 14:05:01 GMT, "peterlsutton"
wrote:


Many thanks Rod - that has been really useful. I have just ordered a
controller from that site. I couldn't find such an item with Google. I may
well build my own propagator, with an added light source. I know that a
couple of inches of sand in the propagator will even out lateral temperature
differances, but it eats into the height available, and is additional
insulation meaning more of the heat will go out sideways and downwards.
Would a metal sheet spread the heat more evenly without the insulation
effect.

Your cyclamen look fantastic, you must have got it right. Do different
types of say herbaceous perennials need different temperatures for seeds and
cuttings and where do you find this information, and what about the light
requirements?

Replying to you and to Keith, yes these are fairly sophisticated,
though elderly technology so a few notes are probably in order as most
of use here use thermostats in some form or other.

First a couple of things to be aware of with this particular
instrument, it was made to be incorporated in some sort of instrument
enclosure so it isn't waterproof and the electrical contacts at the
back are potentially open to inquisitive fingers/screwdrivers so you
need to install it with that in mind.

The guy who sells them is quite helpful if you need help that isn't in
the comprehensive instructions supplied, but really if you have just a
little knowledge of basic electrics you shouldn't have any trouble.
You might find you need to swap the output connections over to make it
switch off at the set temperature rather than switching on - again
it's in the manual.

A thermostat has to exhibit a certain amount of 'Hysteresis' - that is
there has to be a small differential of temperature between switching
on and switching off otherwise it will 'hunt' (it won't know if it's
supposed to be on or off and will switch rapidly between the two
states) This is easily set from the menu - 1 or 2 degrees seems to be
OK for most purposes.

Not much more than an inch of wet sand would probably spread the heat
sufficiently. It would be better if the base of the propagator was a
metel sheet as with the big Hotbox ones otherwise I'd stick with the
damp sand or growing medium.

With the Cyclamen I fill the propagator tray with sifted compost and
sow direct into that. For cuttings I would use sand with trays or pots
bedded firmly on it. The temperature you need to control is at the
base of the cutting so the sensor should be as close as possible to
the base of the cuttings. I usually think in terms of around 20 C.

Seed germination temperatures you can get from a number of sources,
the old Thompson and Morgan seed germination guide is at
http://www.backyardgardener.com/tm.html

As for Cyclamen, http://www.cyclamen.com/ contains all the information
anybody needs to grow commercial F1 hybrid Florists' Cyclamen,
including a full commercial grower's manual if you register on the
site.

If you're going to play with lighting remember that your light source
will contribute heat and will probably make any control of soil
temperature difficult. For lighting requirements specialist advice is
needed for each crop. Dunno if any of the electricity utilites publish
anything these days. years ago there was a useful little book called
'Grow Electric' or something similar. For most amateurs and most pros
other than specialists in particular crops it's not worth going there.

Good thermostatic control is only achievable in simple systems if the
ambient temperature is reasonably stable and is lower than the set
soil temperature so take care siting the propagator - good light out
of direct sun is ideal.

=================================================

Rod

Weed my email address to reply.
http://website.lineone.net/~rodcraddock/index.html

Seed germination temperatures you can get from a number of sources,
the old Thompson and Morgan seed germination guide is at
http://www.backyardgardener.com/tm.html

As for Cyclamen, http://www.cyclamen.com/ contains all the information
anybody needs to grow commercial F1 hybrid Florists' Cyclamen,
including a full commercial grower's manual if you register on the
site.

Again many thanks for your help Rod. Two very good sites and sound
information of your own. One final thought is that this started as I
measured a temperature gradient of 30F from the bottom of a plant pot to the
top (2.5 inches). And it this that raised the question of what temperature
and where do you measure it. I had never considered the point before having
not had a heated propagator, I had naively assumed there was a constant
temperature. But on reflection every propogator must exhibit this. 2
inches of sand or soil is a good insulator, and a feature of good insulators
is that they exhibit a steep temperature gradient across themselves - as in
double glazed windows, 70F one side and 32F a inch away on the other side.
The only way round this is to have the pots lifted off the bottom and so
suspended in warm air that circulates and consequently is all at the same
temperature. I shall have to experiment.

Cheers Peter

peterlsutton wrote or quoted:

I have just bought a large (22" x 15") Sankey 22 watt heated propagator for
?20. I put some cuttings in it and switched it on. With an ambient
temperature of 62F, a thermometer pushed to the bottom of the pot registers
a temperature of 98F, in the middle of the pot it is 85F and resting on top
it is 72F. I have compared the thermometer with another and am happy that
it is accurate. The propagator is placed on a sheet of polystyrene.

This sounds as though it could fry cuttings pushed in too deep. What
temperatures should I be using and at what measurement point. It has only
been on for 36 hours so far and nothing has died yet. Presumably this steep
gradient is normal, irrespective of the actual temperatures.

The bottom of my propagator seems to get very hot as well - though
plants don't seem to object *too* much.

I sometimes balance things on jam jar lids inside the propagator to stop
everything from drying out too quickly - and prevent the heat from
going straight into the bottom of the plant pots.
--
__________
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