Advantages, pros and cons of propogators/heating mats

Is one better than the other if so, why?

I have an old heated propogator, recently obtained and it has no temperature control on it, its a little bigger than an A3 sheet of paper...the base gets luke warm to the touch, is this about right? or is more control needed?

Many thanks!

Steve...

 

Steve - its probably OK, but it depends on what you want to do and where you want to do it.

I have a heated propogator like yours that takes a couple of full size seed trays. I used an energy meter to find out that it was about 22 watts. What this means is that, when its on, it raises the temperature inside the propogator by about 5C to 10C above ambient. If you use it in the summer when the ambient is 20C outside you will get 30C inside. But if it is in a greenhouse when the ambient temperature is -20C, inside the propogator it will only be -10C!

I fitted a quite expensive temperature controller to mine (as I like toys) - it cost twice as much as the propogator itself! But I needn't have bothed. The thermostat is set to 27C, but even inside the house it rarely reaches that because the heater is not powerful enough.

I naively assumed that the temperature inside the propogator would be constant. but that is not true. Compost is a good insulator like a duvet. If you fill the propogator with compost, you have effectively put a duvet over the heater. The temperature under the duvet, ie at the bottom of the pot of compost will be 10C or 15C higher than the temperture on top of the duvet, ie at the top of the pot - and I could measure this with the thermocouple. At this point I gave up. The whole system is not as precise as I would have liked it to be.

Overall my conclusions are that mine works well just as it is. If you put a sheet of polystyrene under the propogator, you will prevent heat loss downwards and get a slightly higher temperature. But for best effect I use mine inside the house, where it is good for germinating seeds. But once seeds have germinated they need high levels of light, if they are not to go lanky. So my propogator is inside a light box. The plants love it - I have summer bedding plants flowering like crazy at this very moment!

 

I have tried the heated, single tray type of propagator you describe and agree with all PeterS says about their use. I now do most of my seed propagation in the same size unheated seed trays, they can have either the hard plastic clear covers or the cheaper thin plastic tops, both work well in the house and as Peter says, as soon as the seeds have germinated it's important to give them as much light as possible. An unheated greenhouse is the ideal next stage for most seedlings but you can, with careful management, bring them on using sunny windowsills so if you are using this method it's best not to start germination too early though I'll be starting some chilli seeds in early Feb (roll on) good luck.