Topic: cold Frame heating advise please

[yeahman]

I've just build a cold from from 4 by 2 wood and a showerscreen door. It'll sit in against the house on the south facing side. it's approx 5 x 2 foot. I'd like to use half of it for growing herbs all year round and other half for seed & plant propergation to be transplanted at the allotment.

This is where I get stuck I want to heat it appropriately. soil warming cables come to mind and i'm thinking about 30 foot, 15 foot in sand trays and 15 foot in the soil under the herb garden. what I'd like to know is:
 - will I need a thermostat - or should i just control it manually with a time switch (alot cheaper)?
 - do all soil warming cables have a metal safety core?
 - will this be enough to warm not just the soil but also the air tempurature (I'll make sure it's well sealed and covered with blankets at night)?
 - If this is not enough to heat it, what's the best solution - parafin heater or heating tubes or maybe a light.

Please let me know your thoughts and give me any advise as i'm really new to this. :)

[Old bird]

Hi Yeahman

Not being silly - but why are you trying to heat a "Cold Frame".  I can understand heating a greenhouse and propagator buy surely the "cold frame" is the bit between the greenhouse and the outside!

Probably me being thick again or have I lost the plot!

Old Bird

 ;D

[yeahman]

 Hi old bird

you're right about the cold frame's correct use. Mynes really going to be a warm frame for propergation and an all year round herb garden.

do you have a heated greenhouse?

[Tee Gee]

Lots of questions there Yeahman but I will have a go at answering them but I must emphasise this is my opinion and is no way meant to detract from your ideas.

I want to heat it appropriately. soil warming cables come to mind and i'm thinking about 30 foot, 15 foot in sand trays and 15 foot in the soil under the herb garden.

I would forget about heating the herb garden and concentrate 100% of the heat in the propagating area.

will I need a thermostat - or should i just control it manually with a time switch (a lot cheaper)?

I am not sure you are correct in saying its a lot cheaper!

Let me explain;

1) You have better control with a rod stat and in the long term (they last for many years) it could work out cheaper.

2) If using a time switch what is to say you won't have a cold snap when the 'time setting' is at the 'OFF' position?

This may cause you to lose your entire stock and how much will that have cost?

do all soil warming cables have a metal safety core?

I am not sure what you mean here but the cable has an inner copper core surrounded by an armoured pvc sleeve/coating. I think, if my memory serve me correctly, the power is AC rather than DC and this heats up the inner core.

If you buy a kite marked product you should be OK

will this be enough to warm not just the soil but also the air temperature (I'll make sure it's well sealed and covered with blankets at night)?

Not really as you know it is a SOIL warming cable.

Admittedly because hot air rises you will get a degree or two of increased temperature just above soil level (which I think is in your mind)

You could rig up  a cover/cloche and position this about 3"-4" above soil level and this should help a little.

If this is not enough to heat it, what's the best solution - parafin heater or heating tubes or maybe a light.

I would use paraffin as a last resort it tends to create lots of condensation. Plus if you do not buy the right type you could kill off your plants.

With a bit of careful planning and insulation I think you might find that you might not need any supplementary heat.

High temperature are only required (generally) for germination purposes, once germinated plants will survive much lower temperatures particularly if you keep them on the dry side.

I have placed a thermometer in a plant pot when the surrounding air temperature was near freezing and the root ball was registering 5° warmer.

I hope that helps with your decision making at the end of the day the choice is yours.

This is how I heat up my greenhouse; http://tinyurl.com/2fpaov

[GrannieAnnie]

We just had our first very successful winter with a cold frame and are still picking loose leaf lettuce from it. No heat cables, no electricity. Left over glass window for 1/2 of the top and the other half is a window that opens based on the temp outside- when it gets to 70 degrees F. the gel in the arm expands and opens the vent window automatically. I don't have to be home all the time to open it. It has sun much of the day and could heat up quickly and fry everything.

I put it together with bubble wrap fitted over a metal frame taken from a cheap plastic green house which hadn't held up.  We were afraid the bubble wrap would tear in the wind (used heavy tape to fit it) but it hasn't.  It looks like the dickens as you can imagine but cost nothing except the automatic arm.

After that success I'll experiment with different types of lettuce  next Fall, maybe some bok choi also.

[yeahman]

Tee gee thanks for advice, I'm going to get a 3m cable with a thermostat and cover up well in winter with the odd flask of hot water to keep things warmish on the cold nights.

I won't try to warm the herb garden either. Thanks both for your advise.

[Tee Gee]

odd flask of hot water to keep things warmish on the cold nights.

I think if you get some 'nightlight' candles and put one in an empty bean can or similar this will radiate a little heat for longer than hot water.

To take this idea a stage further place candle/s on a base e. g. a wall tile, put one in each corner of your coldframe sit the candle on the tiles.

Drill a few holes (breather holes) in the bottom of the tin/s sit the tin/s upside down over the candle/s and voila you have a draught proof radiator/s.

I have even seen this idea developed further by putting an electric light fitting into the tin.

The heat radiating from the bulb heats the tin and again you have a radiator.

But always remember......electricity and water don't mix

I'm going to get a 3m cable with a thermostat

Are you sure you want 3 metres(10ft-37watt) I would have thought it better to get the next size up i.e. 20ft -75 watt which will only cost you around an extra fiver.

This will allow you to heat your whole coldframe if the need arises or make the heat more concentrated if you do half your coldframe.

That is spread the cable a little closer than the norm.

What you must remember you are heating the soil meaning some of the heat will spread downwards.

With my system i.e. a foil covered polystyrene base the heat only goes upwards where I want it.

I'll leave these thoughts with you.

[yeahman]

you read my mind tee gee, I was wondering if it needed more cable, so I'm going to do just that - buy another 10' more.

As for the radiator candles - wicked idea mate

Also as far as covering up over night, do you know where I can get some industrial thick bubble rap from?

[cambourne7]

I would go for a low tech solution and dig out the bottom and fill it with horse manure and use its natural heat to help the plants.

[yeahman]

Didn't ever think that'd work - brilliant idea! I think i may do this for the herb garden side of the frame.

Do you have any idea how long the warmth will remain, can I add compost with it to keep the warmth?

I've just ordered 12m warming cable and a thermostat for the propagation of seeds

is there any way to attach pictures in this forum?