Heat mat and excessive drying of soil

Hi all,

I am new on the forum and have been reading some wonderful stuff on here. I am a newbie at seed starting, and I am having some issues either with bad seeds or maybe my heat mat. Most of my seedlings I have are doing very well but they are not on the heat mat. But, I happen to have 3 trays on a heat mat and have excessive drying in those trays. I did not do anything different during planting. The lights are the same. I am using a soilless seedling mix. And I did have humidity domes over the trays. I have now taken them off as they did not seem to be helping. The same drying whether they are on or off. I have pretty much given up on the seeds in them. They are 72 cell trays, they sit in a 1020 tray on top of the heat mat. I only have a few sprouts in each and I planted in mid-jan. I have re-ordered my seeds in case I got a bad batch, but I don't want to have the same thing happen when I replant. I don't know if the seeds were bad, and I have different flowers in each tray. 3 types of Begonias in one, Marine Bells in one with 1 row of Impatiens, and Amethyst in the other with 1 row of the same Impatiens. I am wondering if anyone can tell me if it is typical to have excessive drying with a heat mat and maybe get some idea for a solution. Will appreciate any info #frustrated

I'm just taking a guess here, but I think that a heat mat plus lights is overkill. I don't use them in combination. My lights raise the temperature to the 70 degrees necessary for germination. A heat mat tends to raise the temperature 10 to 20 degrees more. I think that the combination is actually creating too much heat for your plants. The excessive drying, I think, is a signal. The only seeds I put on heat mats are heliotrope, which require very high heat for germination. I use heat mats only with standard lighting, not plant lighting.

My suggestion would be to remove the heat mat and work with the lights only. You would be amazed how warm they are. On another thread Pam mentions using a heat mat in windows during the winter, when the ambient air is cold.

Hi lilmiss44 and welcome to Dave’s Garden! You’ll find the folks here to be very friendly and helpful.

Sorry to hear about your excessive soil drying problem. Whether or not you’ll benefit from using a heating mat will, of course, depend on where you’re starting your seeds. If you’re trying to start your seeds in a cold unheated area, heating mats that are controlled by a thermostat can be very helpful. On the other hand, if you’re using your heating mat without any type of temperature control, that may well be your problem. As DonnaMack has mentioned, they will often raise the soil temperature by 10 degrees or more unless controlled.

I start all my seeds in my basement and usually I do use heat mats, but only until the seeds sprout and break the surface of the soil. In fact, your plants will do best if the soil is kept on the cool side (maybe 60 to 65 degrees) after germination. I also remove the domes at the same time I remove the heat mats. Leaving the humidity domes on too long can result in root rot, leggy growth, damp-off and other fungus issues.

Hope this is helpful and I wish you the best with your seed starting.

Art

I agree with Art. He makes some excellent points which I did not.

Once a number of your seeds have germinated, it is wise to remove the dome covers, at least from the ones that have germinated. That is also what I do. I sometimes tilt them so that the seeds that have not germinated are covered.

While you are waiting for seeds to germinate, do keep a close eye on them. which I'm sure you do. The needs of individual seeds can be different in the same tray at the same time. I will often lift seeds from individual cells and pot them up because they are yelling "get me out of here!" while others are syaing as the tune goes "Give me just a little more time!"

Best,

Donna

Thank you all so much for the information.

I should have included the part where I am starting them in my garage which is not heated and usually is pretty cool. I am in Oregon though so we don't get really cold here very often. I have a temp gage that shows the garage outside the stand I have set up is about 50-60 deg most of the time. I also put one in the stand that shows about 70-80 deg as it is set up now.

I have read many articles and forums where that should be perfect conditions for growing and keeping the soil warm. If the outside temp is 70-80, the soil temp would be about 5-10 deg cooler than that. I figured the difference in temp was because of the lights and the heat mat together. It does make sense tho, for the heat mat/light shelf to be too warm causing the dryness.

I have the lights on a timer and they go off at night from 11p - 7a. And mostly what I was concerned about is my other seedlings and night time temps. I have thought about turning off the heat mat, but don't want to hurt the seedlings that are doing great. I have had very few sprouts with the ones on the heat mat, like only about 3-4 out of 60 cells and dont think I will get anymore from those trays. I plan to replant those and try again.

If my growing seedlings will not be bothered by turning off the heat mat, I will try that. And, the heat mat is not on a thermostat. I am enclosing pictures of my set up. As you can see the shelf with the heat mat/2nd shelf is not sprouting and I planted those first. I am including some pix to show my set up. Again, thank you all for the info.

Hi again lilmiss44,

Well, I’ll give you my idea of what might be the problem. The very reason we use the dome covers is to keep the surface of the growing medium from drying out too fast during the germination period. Most seeds are placed either on the surface or very close to it. If the surface dries out, the seeds won’t germinate.

In your case (since you’re unable to control the amount of heat from the heat mat) the soil probably gets too warm if the domes are left on (trapping too much of that heat). If you remove the domes, the soil temperature may be fine (since your garage is pretty cool anyway). However, the surface of the growing medium is going to dry out too fast without the domes.

In other words, I think the problem you’re having is a combination of using an uncontrolled heat mat and not using the domes. The ideal set-up is to have the heat mat on a thermostat. The thermostats have a small sensor that you insert into the soil. The dome cover is left on during the germination period. When you see a very slight mist on the inside of the dome, the moisture is just right (and the surface will not dry out). If you see beads of water running down the inside walls of the dome, you have the soil too wet and the domes should be removed for awhile.

Just my idea of it, of course. Anyway, whatever you decide to do, I hope you have better luck next time. Solving problems can sometime take awhile, so be patient and keep trying.

Art

One last point. You have the plants under lights for 8 hours. I always leave mine on much longer - 14 to 18 hours. There is a range but, it is definitely longer than 8.

DonnaMack,

I think she has her lights off for 8 hours :-)

Art

My apologies - 8 hours off is excellent. Detail. Donna, detail!

Thank you both so much for the info. I did have really bad beading of water on the domes when they were on and still had drying so I decided to just remove them. unfortunately I could not afford to buy a heat mat with a temp gage so opted for the cheaper version.

But, I have turned off the heat mat for now. I will keep an eye on temp and see if the lights are enough for the garage. I do have a front cover so I can close it up if it cools too much.

Again,
Thanks so much!
Karen

Come on back if we can help!

Karen, I would love to hear your final conclusions even if it is a month or a year from now. It seems to me that the only people we can LEARN from are the people who are still experimenting to find what works for them. Having a problem, then chnaging some things, then NOT having the problem is something we can all learn from.

Once people find a method that works for them, all we know is that "it works there" and not necessarily WHY.

I have a book on learning from engineering disasters. Every time a bridge or building falls down, architects learn a lot about "why" and "how" and "how NOT to". Bridges that were built the same old way and just keep standing don't teach us anything NEW, and to duplicate their success, we probably have to du0licate the situations under which they succeeded.

I've heard from many sources that seedlings often DON'T like the soil as warm as the seeds wanted it. Thus most people will simultaneously remove the humidity dome AND the heat mat as soon as seedlings emerge from the soil.

It sounds as if the cool, dry air in the garage makes it a balancing act between soil-too-warm-and-wet, or soil-too-dry.

Hello all, and RickCorey_WA I certainly will be around so I will keep you updated on how it goes.

I can say my seedlings were not affected one bit by turning off the heat mat. YAY! And, I have replanted all the others seeds that I mentioned above and am not having the drying problem this time. So, that must have been because of the heat mat. Now I'm just waiting on the seeds to sprout. It may be a few weeks.

I can "almost" certainly say, I probably wont use a heat mat again. Not really sure the ones with the temp control that Art33 mentioned are worth the money they cost, at least not for my little set up. I think like DonnaMack said, the lights are warm enough.

I am still using the domes until I see sprouts, and then they come right off even if not all cells are sprouting. If they are lightly misty I just keep an eye on them, but if they get kinda beady with water drops, I take them off, let the tray get some air, wipe the dome down and put it back on a little later. If it looks like it needs a little sprits, I spray it lightly first. Seems to be working.

One thing I may change up next year is not mixing flowers on the same tray. I have put flower seeds together that were suppose to have about the same germination time, but seems like one will sprout way earlier than the other. I will have to evaluate that more over this season. i am finding germination rates very unpredictable. I have had seeds that were suppose to take 2 weeks, and they popped up in 4 days. Crazy.


It seems to be a balancing act on everything. I will come back and let yall know how the germination goes in the next month or so.

I really appreciate all the help.
Happy Growing
Karen

I had good results with the heat mat years ago when it was new. But the last time I used it, I had trouble with my stuff getting too warm & dry, too. I stopped using it for a few years but this year I thought I would try a new thermostat. Without it, I started stuff on a shelf ABOVE the lights near the ceiling and also on top of the refridgerator and moved them under lights at the first sign of sprouting.

>> If they are lightly misty I just keep an eye on them, but if they get kinda beady with water drops, I take them off, let the tray get some air, wipe the dome down and put it back on a little later. If it looks like it needs a little sprits, I spray it lightly first.

That's what I do, too.

>> One thing I may change up next year is not mixing flowers on the same tray. I have put flower seeds together that were suppose to have about the same germination time, but seems like one will sprout way earlier than the other.

That's one advantage of the flimsy "6-pack" tear-able cells. You can very easily tear a tray into 4, 6 or 12 sections. Then each section can be planted with all-one-variety. When one section has several seedlings emerged, you can move that section to another tray with no humidity dome, and maybe to a cooler location.

I even cut up my propagation trays for the same reason. That's a little tricky because you need thin, stiff scissors or a knife plus dexterity. It's easy to slip and tear the side of a cell instead of cutting between cells.

When all the seeds in a section are the same, that section only needs one seed label. But I use mini-blind-slats cut in half the long way as labels, and also to support plastic film above the soil surface.

I happen to have a roll of 18" wide Saran Wrap. Restaurant supply stores have them, and I found one at a Sam's Club or Costco.

A little late to this conversation, but I've noticed that not all my heat mats are the same. I discovered this a couple of years ago when all the cells in the middle of a tray didn't germinate but all the outside ones did. I found that the heat mat was much warmer in the middle. I still use the mat but I use a thermostat stuck in the middle to regulate the max temp. Like others as soon as I see they little guys peeking out I take them off heat and use lights.

DanSt - I noticed that too on mine, good idea if I chose to try using it again in the future. Thanks!

Karen,

I too mixed various seeds in one tray, and it was a disaster. The seeds that germinated first needed to be off the heat mats and have the dome off, but the rest of the cells needed that environment! I have since cut my trays apart into smaller groups, depending on how many seeds of one variety I want to sow. I use saran wrap as domes and then each seed group can be treated as they germinate.

Good luck!

>> I have since cut my trays apart into smaller groups, depending on how many seeds of one variety I want to sow. I use saran wrap as domes ...

Yes! I do the exact same thing.

I've been looking for, but not ye found, a good "heat spreader" for my one heating mat. Something like a cookie sheet, but without the right-angle bend at one side.

another approach might be to insert a small square of some thin insulator right in the center of the heat mat, so that the heat had to diffuse around it, making the edges warmer and the center cooler.

Some day!

Rick, aluminum is a good heat conductor; have you ever seen those rectangle plate type grates they use to defrost meat in a hurry? They successfully diffuse cold as well.

A baking pan with the edges could be turned upside down, the heat mat placed on top and another pan the same size turned upside down over the previous one, basically nesting. Actually, I think a piece of wood (that doesn't absorb heat as much) could be better if it was the same footprint as your mat and the same height (or higher) as the lip of your pan. That way the heat is more deflected upward towards your seed tray.

If you're handy the top pan could have a cutout with the edges burnished for the cord. Just a thought.

As I think that particular heat mat brand (the one I think I have) is universally problematic, It would behoove me to purchase a piece of stock aluminum the same size as my heat mat.

>> rectangle plate type grates they use to defrost meat in a hurry?

I haven't seen those, but I have thought of cutting the flat bottom from a heavy Aluminum turkey-roasting-pan. Then maybe cut the sides and stomp them flat also.

I like your ideas about INVERTING a baking pan. That would trap the warmed air and spread it very uniformly across the pan. But wouldn't the top-most pan need to be as big as two (or three) 1020 trays side-by-side?

If you could make a box with floor and sides, that would confine the warmth. If the 1020 trays fit tightly together over that box, and sealed enough to keep warm air from just flowing up and out freely, one pad could heat three or even more trays fairly uniformly. Of course, if the pad was only 17 watts, it wouldn't warm three trays VERY MUCH.

Hmm, I'll think about the box idea. Sounds like a project for me to work on...I like projects. I'll start another thread when I think I have it figured out.

Regarding the edges of your turkey roaster, it sounds like a lot of work. Give me the exact dimensions of what you'd be looking for, I think I have a source to purchase at a real good price.

>>
Regarding the edges of your turkey roaster, it sounds like a lot of work.

The turkey pans I;m thinking of are like extra-thick aluminum foil. I assumed they would be around one dollar, but I haven't priced them. I was thinking along the lines of "cut-cut, stomp-stomp" with a rather cheesy-looking outcome.

The sizes I was thinking of would have one dimension around 22" (The length of a 1020 tray plus very little). The other dimension would hold 2, 3 or 4 1020 trays, so 2', 3' or 4'. But if I wanted to spread one heat mat over 4 trays, it would be pretty feeble no matter how well I insulated it. So just 2' x 22" and 3' x 22".

Okay, I'll D-mail you when I get some numbers.

Do anyone in the hot states or in the tropical region use Heating mats? My Mom lives in the tropics and she asked me to buy her a heating mat.I never used them and I was contemplating to buy one but do not know what is the best size to buy.

I have and use a 4' one bc I start tomato, pepper and eggplant seeds in the house, they need heat to germinate. Its hot here a lot of the time but it gets cold too.

Thank you very much 1lisac, I will purchase two of them .

I use them for peppers, tomatoes, and eggplants, also. I use 3" or 4" plastic pots and cover the pot with pieces of scrap glass which I cut from larger pieces obtained from any glass company. They always have plenty cluttering up their shops and are more than happy to get rid of it. I cut pieces just large enough to cover the pot and then slide it over the edge just enough to allow air circulation and prevent excessive heat build-up. This technique greatly reduces the danger of having the soil mix get excessively dry. Once I see signs of germination, I remove the glass.