They are called heating cables, soil heating cables, soil warming cables, etc. They can be found in any number of gardening supply websites, catalogs, garden centers, etc. Be sure to get the kind with an in-line thermostat that will regulate the operation of the cable to maintain the soil at a steady 70 something.

I'll attach some google images on these cables. If you have ANY questions about how to use them, please let me know. I've used them exclusively for over 20 years. Gro-Quick is one commonly found name brand.

Here is a link that might be useful: Click here

you will note.. from rhiz's link.. they are usually buried in a sand table ...

a mat can simply be spread on any flat surface ...

how about more facts on the application.. before we blindly lead you into buying something that you cant even name ... my gut suspects cable will be way over the top for what you need ...

i got my mat .. for indoor use.. at a beer making store .... i think they use them to sprout barley or whatever .... try the yellow pages ....

ken

The link provided above is the best I have ever seen on whats available. I used the grow quick cable for years with no trouble and only replaced it when I needed a larger area heated. I found any cable to be very inefficient buried in sand. Sand is a very poor conductor of heat, better when wet, but impossible to keep wet. My cables are sandwiched between a foam base and an aluminum sheet on top. The thermostat built in to the grow quick cables worked very well but does not allow for changing the setting from the 70 degree fixed. Some times you may want to increase up to 85 for some germinations. My current set up uses an adjustable thermostat, secured to the aluminum plate, so the whole plate(6x3feet) is the same temperature. Al

Linnea,

I prefer to use heating mats, because they don't need to be buried in anything and because they can be used with an adjustable thermostat, whose sensor can be placed where you want it. I submerge my heat-mat sensors in one of my seedling pots (I start my seeds in 3-inch pots to avoid disturbing their roots.) My seedlings are on chrome wire steel shelves, so I put a layer of scrap corrugated board down under the heating mat to keep from losing heat downward. You don't have to use a thermostat with a heat mat, because they get gently warm and are waterproof.

ZM
(not associated with any product or vendor mentioned)

The heating cables are useful (really) only to those who start their seeds in germination flats, not in pots. I don't use sand as the germination medium, but a regular potting medium. I've never used sand (for the germination of seeds).

That's how it's largely done at the commercial level, how I learned to do it in college and as an intern, and how I did it myself for many years in production greenhouses...and now as my hobby! Transplanting does not harm the seedlings, as long as it's done early and one knows a couple of little techniques. I would expect very close to a 100% success rate from the germination flat to the cell packs.

By using germination flats, I greatly reduce my space requirements. Two ordinary flats will produce hundreds of seedlings, which take up more indoor space than I have.

So, linnea, what are your plans for the process: germination flats or individual pots? I saw some reasonably priced mats in the new Lee Valley catalog, but can't speak to how good they are or how long they will last. Of course, the cables are quite inexpensive.

Thanks for the replies. Yes, I should have been more specific! That's what comes of posting right before bedtime....

I would use them for starting tropical bulbs like caladiums, plus mostly annual flower seeds. I'm just recently wanting to get back into growing from seed; I last did it about 20-odd years ago BK (before kids). I had a heat mat back them, but it got lost in the interim. The initial interest was for the bulbs, then I thought, what the heck....

At least initially I won't be doing much. Though everything I start in gardening tends to mushroom very quickly (I was going to say "snowballs" but thought "mushrooms" was more appropriate). I thought of the cables since the heat mat only fits under one flat, and my caladiums alone cover more than that.

As far as the seedlings are concerned, I'd use small individual pots or cell packs. Though, rhizo, you have me thinking about those germination flats.....are you using the kind of flat, 8" x 8" or so, that fits into a larger tray?

ZM, can that kind of thermostat be used with any heat mat? I wonder if you can plug more than one mat into the same thermostat.

I saw someone else was using Christmas lights. (Don't laugh at me for asking! I'm an artist and get into re-purposing a lot. ) They didn't specify what kind, but I'm guessing "rope lights," the kind in the tube. It got my attention because I have a lot of those already that came with my post-Christmas display model Christmas tree. I already used two sets to make above-bookshelf indirect lighting, and noticed they produce a soft warmth. I should put a thermometer on top and see how much.

my heat mat is about 4 by 2 feet ... 4 to 5 trays would fit on it ... 72 degrees ... no thermo ... i have no recollection what i paid for it 20 years ago ... at the beer making store ...

check out the link.. the sky is the limit ...

ken

Here is a link that might be useful: link

I start a great variety of seeds, and seldom need more than 50 of any one. I can start up to fifty seeds in a four inch nursery pot. I never mix varieties in one pot as the germination time varies so much that I would sacrifice seeds not yet germinated to save those that had. At any one time on my bottom heater I will have a mix of seed pots and tented pots of cuttings, so there is seldom any space to spare even with a 3x6 foot heater. Most seedlings transplant very well from the seed starting pot into sixpac cells, with almost no losses. For those seeds I do not wish to transplant I use "root trainers" which open without disturbing roots at all. These hold 32 plants which is usually all I want. Al

linnea, I use a standard plastic nursery flat which measures somewhere around 11" X 21" or thereabouts.

The cells fit perfectly inside those same flats. I prefer to use the cell packs that fit either 36 or 48 cells into the flat. I just like a bigger root system when I plant them than the 72s allow.

This year I kept my germination flats to just two. I was able to transplant every thing a few weeks ago and have 18 flats (with the cell packs inside) of pretty plants ready to go into the ground. Somewhere around 700 plants. They've been sitting outside since I transplanted them, benefiting from the direct sunlight, cool nights, and fresh air. I did have to scoot them inside when we had hail and torrents of rain, lol!