Germinating with heat mats

[Neofolis]

I've finally succumbed to the idea that I need to use heat mats.  Having tried germinating using ambient heat in my polytunnel, the results have been less than fantastic and I think part of the problem is that ambient heat doesn't warm the soil as much as solar heat or a heat mat would do.

I have been looking at some reptile heat mats and separate thermostats, but had a few questions.  At the moment, my seeds are in pots on a gravel bed, which is inside a larger container.  Should I put the pots directly onto the heat mat or could the heat mat go below the gravel? which I was hoping would avoid the chance of roots coming into direct contact with the heat source.  Also how much weight can be put on a heat mat without causing any damage?  Are the heat mats safe with moisture on or around them? I assume they are fully sealed and waterproof.  The thermostat I was looking at has a remote sensor, should that be placed in the soil or suspended above the pots?  I assume being designed for terrariums and the like it is designed as an air sensor rather than a soil sensor.  What temperature should I keep thing at?  I think people in the past have mentioned 30°C/86°F for tropical species.  Should the temprature be constant or lower at night?

Here are links to the products I have been looking at.

Heat Mat

Thermostat

[Logolight]

Corey,  all valid questions.  I also looked into getting heat mats for germination during the winter months here in Jax, FL since right now I can only germinate during the summer months.  The only problems I see is the mats will provide only immediate vicinity heat.  Which means that the bottom inch or two of the soil will retain the heat and not where it's needed near the top.  Also, there is a risk of burning the roots if the container is placed directly on the mat itself.  Like you mentioned, the key is to raise the ambient temperature of the entire medium and I don't think heat mats are adequite enough.  

So you can see I temporarlily abandoned the idea until I can figure out a better way that this method would work.  But someone else may have a better experience on heat mats and they can chime in.  Otherwise, I think the best bet would be to use an ambient heat source like solar or a space heater.  I'm working on getting a greenhouse for the winter months and I'm going to add a space heater to hopefully allow all year germination.

Good luck.

Dave

[Kris]

Dear Corey  

iam not an expert in these things,i just want you to know i visited your post and also want to bump it up to the eyes of the pro's.

and i think your country & mine has 230 volts A/c as the mains

so when your placing wet pots,switch of the system while touching it.

while our american friends have the 100 to 110 volts ac mains.

they are preety safe than us.

love,

Kris  

[gavilan1]

Corey, probably best if you look a bit longer and find mats made for germination in a 220v mains configuration.  I have bought mats and controllers from this source here in the US before:

http://www.littlegreenhouse.com/accessory/heaters3.shtml#mat

Perhaps you might contact them about 220v equipment or contact the manufacturer:

http://www.hydrofarm.com

They're in Petaluma, California, but since the box that the mats come in is printed in English, Spanish, and French, Hydrofarm may have a 220v version (and if you're very lucky, a UK distributor).

[eastern.nurseries]

Corey,

What I did was to lay the mat on a sheet of polystyrene 25mm thick then wrap it in 200um black plastic sheet, make sure all joins are on the under side and seal with duct tape. Put the mat on a timber bench that is boxed in so you can cover the mat with about 100mm of clean sharp sand. The sensor for the thermostat goes in the sand flat in the middle of the sand profile. You can then place your pots and trays on top. To regulate temperature of media use a soil thermometer in the pot or tray and adjust thermostat accordingly. A cover of poly carbonate sheeting or clear plastic over the germination bench will help maintain a suitable microclimate but it must be able to breathe.

 Germination temperatures vary according to species, 28-32c is a good place to start for most palms, Phoenix like 37c and Kentias prefer fluctuating temperatures, so there is a learning curve.

 An important observation is that when using bottom heat your media will dry out from the bottom of the media first.

  I have four heat mats 6m x 1m built into enclosed benches that germinate all my palm seeds [ 500000 seeds per rotation ] with excellent results all year round.

[Neofolis]

Thanks for the info Jon and the link Doug.  I will give it a little more thought and do a bit more searching before I commit to buy, but I definitely need to improve my results.

[Steve in Brookings]

For what it's worth:

1.  I bought one of those low-wattage germination mats several years ago.  They're really designed to work by means of conduction:  transmitting heat directly through another solid that is in direct contact.  So terra cotta and stoneware pots make better thermal conductors than plastic ones.  Planting medium is typically full of perlite and/or vermiculite which make good insulators.  You might find that sand retains heat better.  

2.  Your mix will easily dry out if you don't have the containers covered somehow.

3.  You may find that juvenile roots will quickly snake out the bottom of the container and adhere to the heat mat.  Pot them on as soon as they germinate.

4.  The thermostat may not be necessary.  I got one, but I've had better luck just leaving the mat on all the time.  It's a low voltage mat, and I live in a cool climate, so no big deal.  Contrary to what the temperature markings on the dial may lead you to believe, the mat is either on or off at any given time.  The thermostat simply shuts off the current when it senses the desired temperature.  There is a bit of lag time in the sensing, though, so the heat is not as even as you might think.  

5.  Greenhouses aren't necessarily the best germination environments in northern latitudes.  For small lots, I still think the baggie on top of the water heater is hard to beat...hot water provides the most even heat you can get.  The seeds don't need light to germinate but make sure you check them on a regular schedule.