Heat mat usage

[pepperhead212]

I have a 2 tray heat mat, with a thermostat probe, to control the temp, so it doesn't get too hot. The peppers I start on something warmer - the 3/4" slab of metal I have on my range as a griddle, with 4 pilot lights under it. I adjust this to get the vermiculite I start the pepper seeds in between 85 and 90 degrees. When they sprout, I move them upstairs, under the lights, on the heatmat, which is kept between 75° and 80°. The tomatoes sprout on there, in the other tray, and when they seem to be getting larger, some are moved to another tray, under other lights. Eventually, when peppers are getting considerably larger, I can usually shut off the heat - the last few weeks are usually getting warmer in the house.

[MissS]

I don't have a heat mat. I put my seed flats into my oven and leave the interior light on. It keeps the temp at about 87-88 degrees F. Things sprout very quickly in there. I can fit 4 flats in at a time. As soon as they sprout, another tray can go in.

[TahoeQueen]

I use heat mats for everything: tomatoes, peppers, onions, flowers, etc. But once the seeds germinate, I remove the heat mats. Otherwise, they get too leggy.

[GVGardens]

I use a mat 24/hrs a day for peppers, tomatoes, and squash. I move a tray off the mat as soon as everything has germinated. My mats have probes and thermostats.

I actually switched back to using smaller trays because they’re easier to fit on the heat mats and because I’m clumsy and smaller trays are easier to handle.

**But I have 2 tips for you that I figured out before I switched:
1. Put a cookie sheet on the heat mat and then the trays on the cookie sheet. That way, the heat gets dispersed a little more evenly.
2. If they were things I’d grown before and I was pretty confident on germination times, I’d also just seed the middle cells a few days later and let the edges get a head start. So if I knew the tomatoes along the edges always took 3 days longer to germinate, I'd seed the edges on Day 1 and the middle cells on Day 3 (before the edge seeds had come up so it was easier to reach in the middle).

But it was so much easier to go back to smaller trays! Or use individual pots that you can move off the heat.

[slugworth]

I use the mat 24/7 on full size plants in a room that averages 60F
They do dry out faster but worth it.
I have a green tomato on a early boy plant that may be ripe by Easter.

[karstopography]

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My solar powered heat mat. Air temperature is 69°. Soil temperature is 75°. Not much sun today, but I guess enough energy from the sun is getting through to provide some heat. Most of these are squash, watermelon, cucumbers and the like. Most got planted February 1st. I leave these out here unless it gets below 55° or so at night. Last night, they were outside. Seven to Fourteen days, 5 to 10 days, that’s about where most the seeds are for time to germinate at 75-85°. Should be seeing something pop any day now. This far south, I don’t think a heat mat is necessary.

I wonder how much electricity the average heat mat uses per day?

[JRinPA]

Cookie sheet is a good tip, I did aluminum foil one year. Another year I modified an old dresser drawer to hold trays and set the mat inside it, 5" below the tray bottoms. It was good until the basement got warm and then the cheap untreated wood inside started going moldy lol. I forget about that failure.

The mats are generally rated about 18-20 watt of resistance heating for a 10x20 footprint. So .5 kwh per 24 hrs when left on. With the thermostat and soil blocks and humidity dome, it not nearly that much because it is switched off a lot. Two days back I set mine in series with light timer, so only 12 hours. I don't know how much electricity that will save, since now it will need to stay on constant for a while in the morning to take the blocks back up to set temp - 54F to 68F.

Certainly it is not much electric cost compared to the alternative of having to buy plants/food. I only use the heats mats for a week or two per tray. Sweet corn is like 3-4 days.

The 4 ft mat I have is rated at 100 watts but I haven't put my kill-a-watt on it yet.

Took a few days to make the first mistake of the year- when I moved the heat mat and controller on to the light circuit, it worked. Last night I went down to check it, after the timer was done for the day. Dark. So I went back up for a flashlight, and saw that there were some onion emerging loops. This afternoon I went down to find the lights and mat turned off. The power strip they are plugged into was flipped off. I doubt it tripped - I must have toggled it yesterday evening to try to get it turn on, before I got the flashlight. And then left it flipped off. So, no light for most of today and the temp was down at ambient all day.

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So far, the $2 sweet spanish utah seed is looping. But not the dollar tree 25 cent lisbon packs. Those are the first two from left. The third tray is 10 blocks kohlrabi (I think) then 20 blocks of collards showing cotyledons (or they're reversed with kohlrabi) and then the 20 blocks of 2018 spinach seed from my 8 oz bag is showing some sprouts.

The onions sprouted much faster than they did in the kitchen window attempt last year.

I want to start the rest of the onions asap and I guess lettuce.

[GVGardens]

I just did an experiment that might help.

I received some pepper seeds as a gift and felt peer pressured into starting them even though it’s probably too late. So I figured I’d play around. They were Habanada and the Row 7 website says to germinate on a cycle of 90 degrees for 16 hours and 82 degrees for 8 hours every day. I did everything in a small 5.5”x7” tray with 12 cells. 3 cells for Habanada and the rest were extra seeds from peppers I started a while back. I did everything that I'd normally find annoying: A single tray had Capsicum chinense and annum mixed together and peppers with listed germination times ranging for 10 to 28 days.

80% were up by Day 4 and 100% were up by Day 5.
-This is the fastest I’ve ever gotten peppers to germinate and I’d just started some of those same seeds a few weeks ago.
-They all germinated within 18 hours of each other which was surprising since I had 4 varieties in that tray, 2 different species, and listed germination times that differed by weeks. I was expecting it to be very uneven.

Takeaways:
-Cycling to a lower temperature at night doesn’t hurt. It probably helps, as @bower says. My mat wasn’t completely off but it was still 8 degrees cooler at night. Your mileage may vary with other types of plants and other temperatures.
-90/82 definitely germinates peppers faster than my usual constant 84ish. In the past, I just cranked the heat mat up to the highest it would go. With my ambient temp, the mat usually maxed out around 84. My next experiment will be to compare a constant 90 vs 90/82.
-To get the temp to 90, I put the heat mat and tray (with humidity dome) in a cheap, foam cooler. I left the lid off the cooler. The mat was able to heat and hold stably at 90. It probably used less power than when I had it trying to maintain 84 outside of the cooler.
-I think the cooler helped even the temperature out across all cells. Kind of like your drawer, @JRinPA . Might be worth grabbing some dollar store seeds and putting a mat and a 1020 tray in a cooler or on some styrofoam to see if things germinate more evenly? If they do, you could line your grow shelf with styrofoam.

[JRinPA]

That is some good info. Hopefully not too late for your pepper starts. I was thinking I would start some soon for up here. I think I do peppers at 85 the last few years. I grew Habanada and nadapeno two years back.

I figured 68 should be good for onions and the stuff so far. I did the second pack of sweet spanish utah along with Granex as the second planting session. Third session was cabbage broccoli and lettuce. Neither of these plantings are up yet, but, I planted the onion seeds deeper, and have the mat turned off for 12 hrs a night with the lights, and...cellar is down 53F again with this cold. I have some more seeds to start today, though I was waiting for mat space to open up. But it would probably open up faster if I bumped the mats a bit warmer and longer.

So far the first planting dollar tree onion bunching onion seeds have done very little. Someone said, a while back, that they heard/thought that the dollar tree seed was year old seed reclaimed/repacked into smaller envelopes. They are definitely smaller packs (200 mg onion seed instead of 800 mg -1200mg) and old onion is supposed to be slow. This stuff was planted the same time as 1st utah seed from TSC and is still showing very little germination. I keep on watering it.

I have a couple packs of hot pepper from there, cayenne and....serrano. I expect they will take longer than my saved seed from last years jalafuego and romani. But, I'll try that 90/82 cycle when I start some and we'll see how awake those hot pepper seeds are.

[SpringtimeInTheBag]

I've never used a heat mat. Getting peppers to germinate was the big issue so last year I tried one last thing before I went out to get a heat mat and get serious. I used one of those hot/cold gel packs that you can heat in the microwave. I'd microwave it about 5 seconds less than it took to be just warm to the touch on my face. That gave me mid 90s F in temp. Then I'd slide it under the portion of my tray, that was propped up on small peat pots, where the peppers were. When I took soil temp readings ~1 hour later I was getting a 3-5 degree F rise. My peppers came up great. The non-peppers in the adjacent area were mostly on the earlier side by a day or two.

The important caveat is this involved living with my elderly mom with poor circulation. Things just started warmer before the heat pack got involved. I managed to get her out of thirty year old nightgowns that were wafer thin into sherpa fleece pjs and lowered the thermostat a few degrees. We'll see if my trick still works this year.

[bower]

Another trick specifically for pepper seeds is to soak overnight in warm water.
I once had some 'heatless habanero' seed gifted to me with the warning to expect low germination. I do usually soak pepper seeds overnight before putting them in potting mix on the heat mat, but this time I put the little 'pudding cup' of water/seeds onto the heat mat before leaving it turned on overnight. I ended up with near 100% germination of those seeds within a few days, and a shocking surplus of pepper plants.

[NPKNorthTexas]

>>"Put a cookie sheet on the heat mat and then the trays on the cookie sheet. That way, the heat gets dispersed a little more evenly."

I do that too, using a disposable aluminum cookie sheet turned upside down.