Bottom heating

Am looking into bottom heating to root cuttings. Is a mat better or cable? At what temperature?

The temp necessary to grow roots can vary widely. Some of it depends on the plant and some of it depends on the length of time you have and also on the method you use to grow the cuttings. There are books out there that will give you the basic parameters. In general, if you are starting the cuttings in the spring or summer, soil temp should be around 70-75oF. Ambient temps, the air circulating around the plants is not as critical but don't let it get really chilly. If you are starting the cuttings in a standard 11x22 inch tray a mat is convenient but you will need a separate mat for each tray. Some of them have the thermostat as a separate purchase and want you to buy one of those for each mat. Some of the cheaper ones have a 'sort of' thermostat and that is what I use for trays when I am short of space on my light racks. On the racks I use 4 fluouresent bulbs per shelf with a mylar reflector. There are 3 or 4 shelfs in each rack and each shelf will take 5 trays. The waste heat from the lights maintains an excellent soil temp in the shelves above those lights. If you plan on using a cold frame, the cable (which needs to be buried) will be the best bet. Be aware there are many different ways to produce new plants asexually. I once tried to make a complete list and after 3 pages double spaced I gave up. Look at the situation you have concerning space, equipment , etc. before you make your decision or it might wind up being a money pit if you have to invest in a lot of extra equipment. Jessamine

Thanks a lot for your time in answering this thread. I am primarily interested in rooting boxwood, that I have been doing for years with only a 30-40% successs rate, and thought about trying heat mats after talking to a grower.
Will take up your suggestions for the lights, etc. (up to now have been using different types of small enclosed containers (pots, seeding trays). I had pretty good success this past summer rooting softwood cuttings and have been thinking heat might be beneficial (past attempts probably had a soil temp of 60 degrees).
thanks again

Since I haven't seen your setup I can't comment on it but in WVa, you should have really good results with my favorite method of layering and you still have time to do it. Bend a branch down to the ground. Make sure a node is making contact with the soil. Remove extra foliage from the node and scratch the node to reveal the cambium layer. Rub the node with rooting hormone and lay a brick on it. Leave it alone til next spring. If the branch doesn't bend far enough to touch the soil put a pot of soil under it. In the spring, remove the brick and check for a root system. Make a judgement call. If the roots seem to be growing well, cut the connection to the mother plant. If it didn't grow enough, water it with some MiracleGro and replace the brick. Jessamine

Heres a link to one of my old threads showing a heat box I made.
I've been using it for years and it works great. Made from scrap materials.

Paul

http://davesgarden.com/forums/t/182057/

Boxwood is one of plants that doesn't require rooting compound. I have found that just pure sand works better for them as far a medium is concerned. Why? No clue here. I just did my first test this fall and boxwood that I had the best lucky with (if I can keep the cats out of them now).