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

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