Heat mats are used for germination only. Once the seeds sprout and break the surface of the soil they must be removed from the heat mat or it will cook the roots.

But yes, 24/7. The heat must be on continuously until than happens. Turning it off and on just defeats the purpose of using it and the seeds may rot due to the extreme changes in temp.

60 degrees air temp equals approx. 50 degrees soil temp and nothing except some of the leafy greens will germinate at that temp.

Without the thermostat: The mat has a small built in thermometer that acts as safety shut off. It is made to give you approximately 10 degrees above the ambient room temp. But in large rooms that are that cool they will burn themselves out quickly trying to keep up with the room temp. It is trying to heat 'the whole room' and it just can't do that.

So you need to use a thermostat with it OR confine the area it has to respond to in some way. For example, see the post about Styrofoam and duct tape but any sort of small enclosure will work - even a plastic tent over the area. The thermostat allows you to control the exact soil temp.

Dave

This is only my 3rd year with seeds under lights, however I havent used a heat mat at all and seem to get very good germination from my seed.

Because my grow shelves are built in to the wall, they are enclosed on 3 sides already. I hang a mylar reflective blanket (less than $3 in the camping section) over the front of the shelves and the lights have enough heat to easily raise the temp in there 10-15 degrees or more. The room I use is 60 degrees or less.

For seeds that like the soil exceptionally warm, 85 +,and dont need light to germinate, I lay the trays directly on top of the suspended lamps.

It is certainly possible that I would get even better germination with a heat mat, but I cant justify the price of the heat mats in relationship to the price of the seed, for 10% more germination.

I am REALLY new to starting indoors with seeds; but I learned quickly that I didn't need my heat mat. It really depends on how warm your lights are already getting your soil. With lights on and humidity dome on - my soil was HOT. I needed a fan unless I wanted to raise my lights.
In the end, I stil use my heat mat because I turn the lights off for a few hours each day (still haven't figured out why I do that - everyone just says I need to...:) ) . I keep the heat mat on the seeds that haven't germinated to keep the temperature consistent while the light is off. It took some tweeking because I needed to put my flat on chopsticks to raise it off the heat mat. Otherwise - my temp of the seedslings was still going to be too warm.
A digital meat / tea thermometer works well for me to see how things are going. Otherwise, it is a guessing game.

Honnat - I was going to email you this but you don't have an email posted so will put it here in the hopes you'll see it.

With lights on and humidity dome on - my soil was HOT. I needed a fan unless I wanted to raise my lights. It really depends on how warm your lights are already getting your soil.

Then what kind of lights are you using? Fluorescent lights don't put out much heat at all - minimal. Even if they are very old fixtures with built in ballasts it isn't much and newer fixtures don't have ballasts in them. And it is top heat not bottom heat so it would be almost impossible for the lights alone to heat your soil to the very hot level. If in a very small confined space they can eventually WARM it but get it hot would be impossible. Lots of studies have been done on this issue and in over 40 years of growing from seed and measuring soil temps I have never seen any soil temps over 70-75 degrees from lights alone. Something else is going on here, there is some other source of heat causing your problems.

If you are using metal halide or HPS then yes they can produce sufficient heat.

digital meat / tea thermometer

Very different calibration on those. I would seriously question how accurate your thermometer is for measuring soil.

Also do you mean you are leaving seedlings under plastic cover? That's a big no-no.

Dave

Check out my other post under this topic. Nothing wrong with my lights - just too much to have that close.
I do have my humidity dome still on - so far so good. Everything looks super healthy. I keep it open a crack and a fan on to keep some air moving around. I have many seeds that haven't germinated yet, so until they do, I think I'll keep it on (unless I start to notice damp off).

Here is a link that might be useful: Too Hot??

Honnat: what kind of heat mat are you using?

FYI a humidity dome over anything other then seeds that have not germinated is a recipe for disaster. I love to learn by doing, so by all means keep going with what you are doing but please be aware that MANY of us have learned the hard way. and once you see damp off, there is nothing you can do but hopefully save the plants that have not shown ANY signs of the devastating disease.

Keriann~

Nothing wrong with my lights - just too much to have that close.

No one said there is something wrong with your light but asked what type are they? Many here have extensive light set ups with no associated soil heating issues. Personally I run some 25-30 T5 and T8 fixtures in our commercial greenhouses as well as several metal halide and HPS units and there is minimal soil heating from them. We'd be happy to help you correct the issues you are having with more information.

But if you prefer to continue as is then please be aware that your findings and description of your issues is most unusual. So it isn't something one should encourage others to copy. There simply is far to much documented evidence to the contrary.

As Keriann said, a humidity dome over germinated plants - fan or no fan - is a recipe for disaster. Sadly some simply have to learn the lessons the hard way I guess. Good luck.

Dave

Hi Dave.. just a question

Have you seen your HPS lights produce leggy plants because of their high red spectrum? Or do you use HPS for flowers/fruiting plants?

Thanks

Keriann~

Yikes - i feel a little under attack here. Good to see you all care about my seeds so much (I guess...). I prefaced my advice in the first post with "I am REALLY new to this..." I wasn�t trying to lead anyone astray. The only advice that I wanted to give the original poster was that he/she may be getting enough heat from the lights and not need the mat. If I would have used a heat mat - I would have cooked my seeds in a hurry and my light set up is not that extensive (see link below). With lights and meat mat on � my soil temps were soaring over 100 degrees.

I realize keeping the humidity dome on is a bit unorthodox and places me at a higher risk for damp off. The seedlings are tiny and just now developing beyond the cotyledons. They look great so far. However, I think I'll follow your advice in the other thread and separate the cell packs of the two varieties that have germinated. Thanks!

Here is a link that might be useful: My light

Honnat: what kind of mat were you using? or going to use?

Keriann~

Please don't feel attacked. That isn't the intent at all and I'm sorry if you feel that way. We really are just trying to help anyone new to seed starting and save them from suffering the common failures that can be discouraging.

Dave

Should I start my cool weather seeds (snap peas, lettuce, greens) on a heat mat or not? I started snap peas and spinach already on the heat mats and only got 6/33 to germinate. Thanks.

Depends on what setting is on your mat. All those will germinate fine without it as they want soil temps of only 55-65. If it is set too high - such as the temps required for peppers, tomatoes and such - they won't germinate at all well.

Dave

Honat - thanks for the input, I love this kind of discussion. I do what works for me and love reading about everyones' methods and theories. For me mat and dome until sprouting then room temp under lights and fan.

This mat would be used in the heated basement that still is cooler than the upstairs. Should it be enclosed in this case in order to prevent the lights from trying to warm the entire basement?

From my novice experience, it depends on the type of seeds/plant you are growing, how deep the pot(s) are, and how warm the lights get. If you enclose an area, depending on the materials you are using, you can run the risk of mold and, if it's seedlings, weak-stemmed adult plants (though this has mostly just been my experience).

Just found this discussion and I, too, am pretty new at starting seeds indoors. I have started pepper seeds a week ago and the heat mat has worked like a charm. In 6 days I had sprouts popping up. Once that happened, I immediately put the tray under lights on the pad with the dome still on it. So far I have about 40% of my seeds germinating but I know it's still early...especially for peppers. I expect the rest to start showing up in the next week too, but my question is this... When do I turn off the heat mat? The seeds need the warmth to germinate, but will the ones already germinated get cooked? When do I take the dome off? Thanks in advance for your help.

Hi wolife,

All of the seeds will not germinate at the same time, that’s normal. Even so, it’s usually recommended to remove the heat mat and dome pretty shortly after you start seeing the first one’s germinate (especially with 40% germination). Otherwise, you take the chance of killing the one’s that have germinated.

The heat mat helps the seeds germinate sooner, but that doesn’t mean that the seeds won’t germinate without it. They may take a little longer, but they will probably sprout just fine. My suggestion would be to go ahead and remove both the heat mat and the dome at this time.

Hope this is helpful,

Art

I devised this elaborate germination chamber a few years back under the technical direction of dig dirt Dave....... Crude but effective! You STILL da man Dave! http://i6.photobucket.com/albums/y240/gltrap54/001_zpser9igdiq.jpg

Greetings. I'm new to the growing scene and have lots of questions. I've bought lots of supplies and some seeds from a seed bank. I'm having problems getting my seeds to sprout. I live in New York so i grow indoors. I've just bought a propagation tray with a heat may. Can it b used for all seeds? Can I use foxfarm soil as my medium with the tray? I've got other questions and would greatly appreciate some insight. I've been having other problems with my soil drying out under my hips light. Is the light too close to my plants? Thx for the help. E-mail me at mikeem420@gmail.com. thx again

theres no right way or wrong way to sprout seeds its whatever works best for you.i have sprouted them in paper towel, paper towels using tray and heat mat, soil ,soil with dome and mat,also a paper towel in a zip lock bag, also there is a glass of water for certain bigger seeds for 24 hrs.You got to listen to ppl opinions and do research in books also helps better understand things and experiment a little and find what best works for you.for me the paper towel and tray with heatmat worx for me.also foxfarm soil is good i use it in my mixture,and yes the light is probably too close move it up alil should help.through what ever feeding routine you do find what worx best for you and dont be scared.there is no set right or wrong way to do it.

Hi Everyone,
I'm jumping into this conversation with another question. Feel free to send to a link as I'm sure this question has been asked a million times.
I'm starting Alpine Strawberries and Tomatoes.
I'm using a Sun Blaze light fixture with 4ct, T5, fluorescent lights per fixture. No reflectors. My seeds are on wire shelving and by a window. Outside temp is still below 32 at night and around 45 days. The room is 60 + degrees. With no heat mat and seedlings covered, my lights still give enough heat to create condensation.
1) One fixture literally raises the ambient temp in the room. Does that seem strangely hot for these types of lights?
2) Given the variables: by a window, hot lights, covered, should I use a mat?
3) How many hours of artificial light should I give them?
4) Any thoughts on mixing bulbs (Red & Blue) in the same fixture. Should I throw in a red spectrum bulb or two if I want my Alpines to bloom? Or best to keep move the Alpines to an all red fixture once they look ready?

Thanks everyone..I bow to your expertise!
Sharron

Interesting post. I've used a heating coil and overhead lights successfully for many years. I have a new heating mat system now (the old one died) and using it as directed, but with the grow lights the temperatures are much too high. I easily get to 35 degrees C. (95 F) Yes, the heating mat is specifically designed for starting seeds and even tells me how many days each seed should take to germinate. Nothing is coming up except the basil. I'm trying (today) using an outlet timer so that it goes off 15 minutes, on 30 for the day. I'll then then have it on all night when the light is off, because it's a cool basement and it will get too cool otherwise (like below 20C / 68F)

What brand is the heat mat...Vivosun? Do you have a thermostat for it? What type of light are you using.

My Vivosun without a thermostat keeps the bottom of the tray at around 77-78F. I use fluorescent lights that do not give off much heat at all.

"Hyindoor" is the brand of seedling heating mat. Like I said I've used this set of grow lights for years. As a matter of fact I was thinking I should buy new bulbs because they must not be putting out enough anymore. I never had this problem before the old bottom heat system stopped working and had to be replaced.. There is no thermostat, but I have one inside that I consult so I can monitor thing. My timer seems to have stopped the problem and gets me to roughly 76F - on half an hour off one hour for the day and on most of the night when the lights are off.