Hello Karyn1.I find the cheapest and most convenient way of getting bottom heat to any plant or seedling is to use undersoil heating cable covered with a fine sandy gravel mix to a depth of around 2 inches.keeping it moist transfers the heat to the bottom of the plants.
Hazel.

Thanks Hazel. The reason I was asking is because I have an extra heating pad from one of my gecko cages. They got moved to another tank and I figured I might be able to find some use for it, oh well.
Karyn

Hello Karyn, you may very well use other sources of botom heat but I find that the undersoil cable is very gentle and almost costs nothing to run.I have two deep propogating bays both sides of one greenhouse on the staging.They have liners then a layer of sandy gravel.The cable is snaked through and a layer of the sandy gravel on top.The sides to keep it all in is made of plywood boards.I do have a large metal heating pad but I find it gets far too hot unless I put polystyrene boards over.I was thinking of cheapness for you as it works for me.
Hazel.

I also use the heating cable, sand and a big 4X2 ft. clear polystyrene box to heat the bottom of my cuttings. I also use a "light dimmer" to control the voltage and therefor the temp. I have found that the cuttings like 90-95 F best

Thanks for the info. We have heating cables in the greenhouses for starting seeds, just not at home. Our greenhouses are a few miles from our house. Is it messy to make that kind of set-up in the house? I'm hoping to build another small GH in the backyard but that hasn't happened yet. lol
Karyn

Karyn, I use the regular heating pds, I just put it under a 10 gal. aquarium turn it on low and set the pots in the tank..works every time, but I do turn it off at night.