Seeding Mat Advice

brian6464(4a)February 16, 2014

I just got two 72 cell trays of pepper seeds going today. I have a heating mat that is wide enough for both trays.

How much time per day should the heating mat be on? Is this a 24 x 7 thing? Or can I turn off for the 10 hours I am at work and then have it on the rest of the time?

Also, is topically spraying the cells with warm water enough or do you actually water them cell by cell. It's a nice sprayer that allows me to wet all cells without disturbing the potting mix as much. The potting mix always seems to shift quite a bit when dropping water in cell by cell.

Just looking for advice on what works best for others. Thanks.

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seysonn(8a WA/HZ 1)

Heat mat should be on 24/7 until the seeds germintae. But you have to make sure that the bottom of the tray does not get warmer than 85F.

WATERING: since the seeds are planted shallow, spay misting should enough. You can also throw a towel, newspaper etc on the tray to prevent drying up. SEEDS NEED TO STAY MOIST TO GERMINATE.

    Bookmark   February 16, 2014 at 8:26PM
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So if I have them in a room that is set to 67 degrees, I should be safe...right? Even if the heat mat tops out around 20 degrees which I think is the max, I would be right at or just above 85 degrees.

And if the mat only adds 10 degrees, I am still at the low end of the germination range of 75 to 90 degrees.

    Bookmark   February 16, 2014 at 9:21PM
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To keep a more even temp.
Put something like foam under your mat if you aren't using a thermostat.
Otherwise the heat mat might go by what it is sitting on rather than soil temp..

It depends on what your mat is sitting on.
If it obsorbs heat easily it won't warm your cells.
Mats are set to keep something like 20 degrees above whatever temp. the mats on.(or whatever contacts the shut off...).
A hot shelf that holds heat will mean cold cells.
Once the shelf gets to temp. and holds it,soil gets cold.
Wire racks in a cold basement could cook your seeds.
Mat is trying to heat the air and running all the time.

Some heat mats used to come with cheap foam to place everything in.
The trays broke easily so people stopped messing with the foam trays everything fit in.

I use sheets of packing foam and a thermostat.

    Bookmark   February 16, 2014 at 9:25PM
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I have the mat sitting on a bath towel on top of a pub table in a room set to 67 degrees.

Would I be better off using something other than a towel?

This post was edited by brian6464 on Sun, Feb 16, 14 at 21:51

    Bookmark   February 16, 2014 at 9:48PM
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I never used anything but scrap foam from work.
Towel might be fine.
I guess if you can check the soil temp. that would be the way to go.
I have a thermostat for my mats.

    Bookmark   February 17, 2014 at 12:12AM
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seysonn(8a WA/HZ 1)

The mat (without any limit control =thermostat) is always on and putting out heat. So in a warm room and insulated bottom(towel etc) the temperature can climb.To give you just and indication : I use a medical Heat Pad. When I put a folded dish towel on it, The temperature on the top can get up to 100F. So I had to add more padding to bring the temperature of container(bottom) with seeds down to 85F. I have a digital kitchen thermometer which is very handy and accurate that is how I know it.

BTW: you can even germinate in room temperatures. The only difference is that instead ONE week it might take TWO weeks.

    Bookmark   February 17, 2014 at 1:15AM
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To illustrate Smoke's point about heat absorption / loss based on the surface your mat is on, see the table below (click it for a larger view)..

A few years ago, on a slow day, I ran a few tests. For what it's worth, I do my germination in trays on mats in styrofoam tray boxes.

For reference, here's a shot of a crude homemade styrofoam box.


    Bookmark   February 17, 2014 at 4:22PM
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Now that you have sufficiently scared me into getting a thermostat (to be delivered Wed from Amazon), I'll cease using the heat mat until I can regulate the temp. I purchased the Hydrofarm one where u plug it into the wall and then the mat into the thermostat.

    Bookmark   February 17, 2014 at 6:40PM
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If you got the digital one, that's the one most of us use and Amazon has the best price.

I'm sure you'll find it a great aid to regulating temps in your germination tray(s)


Here is a link that might be useful: For refference, a 2010 post on heating pads

This post was edited by ottawapepper on Mon, Feb 17, 14 at 18:56

    Bookmark   February 17, 2014 at 6:50PM
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Probably a silly question, but is it absolutely necessary to put the probe in the soil or can I just let it lay between my mat and germination tray.

I realize the most accurate reading of the actual soil temperature would be to put it in the soil, but this means I will also lose a bit of the seal on my humidity dome by having a cord running into the tray.

Just curious what others do. Thanks.

    Bookmark   February 19, 2014 at 10:34PM
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Ottawa and Smoke, thanks for the input.

I have now realized the error of my ways. Even on the heating mat and towel, the soil temp was just slightly above ambient room temp. Since I didn't have Styrofoam or a box to fit my mat size, I literally just covered my two trays with a fleece blanket to trap the heat. Within an hour, the soil temp was up to 78 and holding +/-1.

I'll obviously pull the blanket every day to check for sprouts and check the soil moisture.

Speaking of moisture, I assume the elevated soil temp will speed up the drying process. I've always had a hard time determining the proper amount of water and I think I tended to overwater my seed trays the past couple years. Under my scenario, 2 x 72 cell domed trays on mat under blanket at 78 degrees, it is normal to water every day or is this overkill.

Is there a technical way to measure moisture in the soil?


    Bookmark   February 20, 2014 at 10:39PM
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Here's my 2 cents. I'm sure Smokemaster and others will add anything I miss or their own opinion ;-)

The thermostat probe should be in the soil for best results, that's where I place mine. You really don't have to worry about the small gap caused by the probe wire.

For most pepper varieties the sweet zone for best germination results is 80 - 87 F.

Covering the top with a blanket obviously helps insulate your trays but you're not going to be able to use it once your seeds start sprouting, they're going to need good light.

With respect to watering, even with the heat, with the dome on I rarely have to water more than once every week. The dome should keep things moist. Once your sprouts start growing you'll want to remove the dome to facilitate air flow. If you keep it on you'll risk developing algae or worse damping off fungi. At that point just water when you see your sprouts wilting or the tray feels light like it is just dry starting mix. When the dome is off, If you're still using the heating mat to germinate remaining un-sprouted seeds, you will have to check those cells daily to make sure they don't dry out. I usually use a mister to keep the starter mix moist.

You can buy moisture meters but that would be overkill squared! As you gain more experience you'll develop a watering procedure that works for you and your plants.


This post was edited by ottawapepper on Fri, Feb 21, 14 at 14:31

    Bookmark   February 21, 2014 at 11:12AM
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Alright, I'll bump the thermostat up to 81 degrees. I've fully watered twice in 6 days and used a spray bottle to topically wet it a few days. Even though I was pretty light with the water, I'll still lay off for several days.

Been in the trays for 6 days but only 2 with heat mat and only 1 with soil at 78 degrees. Hoping for some sprouts by middle of next week.

I have a lot of seeds though, so I'll get plenty of practice this year.

    Bookmark   February 21, 2014 at 5:22PM
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I use a string of white christmas tree lights and a few strips of 1" styrofoam under 4 1020 trays. On a 15min on/15min off timer. Temps peak at 85.

Cost me $10 for everything at Menards. After most of the seeds have germinated and the domes come off I just unplug the lights and put them and the styrofoam strips away until next year.

    Bookmark   April 16, 2014 at 2:22AM
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DMForcier(8 DFW)

> "I just unplug the lights and put them ... away until next year"

You mean until Christmas... ;-)

Great idea, btw.

    Bookmark   April 16, 2014 at 12:28PM
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Interesting advice from everyone. I ended up using a thermostat keeping it at 80 degrees with the +/- 2 degree cut off/on points. With the trays full, the moisture content did stay really high and there was no need to water. As seeds sprouted and I removed individual cells, the moisture content starting getting lower and I topically sprayed the remaining cells.

All in all, it worked real well. I'd say I'll probably rig up a styrofoam tray to sit under the mat next year, otherwise there is reall nothing to change.

I did two trays with 72 cells and had a really high germination rate. Now I'm trying to get rid of a bunch of peppers.

    Bookmark   April 16, 2014 at 12:40PM
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DMForcier(8 DFW)

Ah, there's no burden like success...

    Bookmark   April 16, 2014 at 12:58PM
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seysonn(8a WA/HZ 1)

Ah ! Those were the days .
I am all done with. All my plants are outside.

The next battle is fighting the elements outdoors.
Cowboys' work is never done !

    Bookmark   April 16, 2014 at 1:23PM
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