Heat Mat for Seedlings - Help!

Hi all,
This is my first year starting from seeds (I want to start saving my own), and I picked up a seed heat map and a thermostat. Not necessary I know, but people seem to like them! My problem is I’m not sure that it is working properly. I set the thermostat to 90, and it’s been about 5 days with my soil still sitting at 73 which isn’t much higher than ambient room temp (70). Did I get a faulty mat or thermostat? I even moved the mat from the windowsill to a more insulated area. Does it usually take a while to raise soil temp? Any help would be appreciated!

It should heat it up within a day.  Does the thermostat come with a probe that goes in the soil?  If not, maybe the mat senses its own temperature.  Is it around 90 degrees when you stick your hand between the seed tray and the mat?

Evan Kruschke wrote: I picked up a seed heat map and a thermostat.

What make/model are the heat mat and thermostat? Like Mike says, it could be one of those scenarios where the heat mat has an internal thermostat that kicks on at 40 and shuts off at 70 or 75... so even if the thermostat is set to 90, the heat mat shuts off at 70 regardless. Hard to know for sure without knowing the make/model of the mat and thermostat.

Hi Mike,
Yes I bought the temp probe/thermostat with the mat because people were complaining that the mat got too hot otherwise. The thermostat is supposed to measure the heat of the soil and only bring the soil up to the temp that I set. However, even when I just plugged the mat in by itself, I don’t believe it got very hot. So maybe I got a faulty mat?

Hmm, could you upload a pic of your set-up?  Maybe we can spot something amiss...

Mike Haasl wrote:Hmm, could you upload a pic of your set-up?  Maybe we can spot something amiss...

Absolutely! You can see the probe going into the Lillian’s Yellow pot. The temp did go up a bit today but it it was a much warmer day today.

That looks like the same heat mat I have. Mine won't go above about 75F. It does seem to be doing the job for my seedlings though.

Abe Coley wrote:

Evan Kruschke wrote: I picked up a seed heat map and a thermostat.

What make/model are the heat mat and thermostat? Like Mike says, it could be one of those scenarios where the heat mat has an internal thermostat that kicks on at 40 and shuts off at 70 or 75... so even if the thermostat is set to 90, the heat mat shuts off at 70 regardless. Hard to know for sure without knowing the make/model of the mat and thermostat.

The model is a Vivosun.

VIVOSUN 10"x20.75" Seedling Heat Mat and Digital Thermostat Combo Set MET Standard https://www.amazon.com/dp/B016MKY7C8/ref=cm_sw_r_cp_api_i_2FFGZ7M834WDZT6363Q7?_encoding=UTF8&psc=1

I have the 10x20 mat. The instructions that came with the thermostat said that it should only take 5 hours to come to temp. But I wasn’t sure if that was the mat or the soil.

What kind of seeds start at 90F?  
We usually start ours at about 70F as our soil outside doesn't get much warmer than that in the summer.  

r ranson wrote:What kind of seeds start at 90F?  
We usually start ours at about 70F as our soil outside doesn't get much warmer than that in the summer.  

I originally had it set to 80 for my peppers and tomatos. However after a few days it was still only sitting at 67 which was my room temp. I put it up to 90 in hopes of getting the soil to 80.

Ah, I see.

My heat mat only raises the temperature about 5 degrees above ambient to a max of 75.  We put shiny insulating bubble wrap like stuff under it and it doesn't lose as much heat to the table and can raise the soil almost 10 degrees F.  

r ranson wrote:Ah, I see.

My heat mat only raises the temperature about 5 degrees above ambient to a max of 75.  We put shiny insulating bubble wrap like stuff under it and it doesn't lose as much heat to the table and can raise the soil almost 10 degrees F.  

That would be a good idea! I was thinking about some cardboard or something under it to save some heat.

Robin Katz wrote: That looks like the same heat mat I have. Mine won't go above about 75F. It does seem to be doing the job for my seedlings though.

I have some other seeds (same plants) not on the heat mat, so I'm kind of doing an experiment to see which germinate fastest!

I use a generic moisture proof heating pad from the drug store. Set on low, it reliably provides bottom heat between 70F and 85F when placed below a metal baking sheet that the cups sit on. The one issue I have with it is that it shuts itself off after an hour, so I use a cheap programmable timer plug to turn it off and back on every other hour. I get very good germination on my peppers with this setup. I might get a real heat mat some day, but I already had all this and it seems to work just fine.

Since Styofoam is evil now and some of those Amazon boxes that show up on my door each week have things packed with Styro in them, I tried putting sheets of the stuff under the heat mat to keep the heat going up to my seedling trays and that seemed to make a noticeable difference.  My latest batch of pepper and tomato seeds are sprouting already, just 72 hrs from being sown.  Good use for something that'd sit in a landfill otherwise and likely will outlive me, plus seems to do the job better than the cardboard I used previously (which will now be used in a new terrace bed out back).  Win-win!    My Vivosun mats are on a shelf in a 55 degree basement but with the Styro beneath they seem to do the job.   Now I just need to keep the seeds alive until transplanting time.

Scott Charles wrote:Since Styofoam is evil now and some of those Amazon boxes that show up on my door each week have things packed with Styro in them, I tried putting sheets of the stuff under the heat mat to keep the heat going up to my seedling trays and that seemed to make a noticeable difference.  My latest batch of pepper and tomato seeds are sprouting already, just 72 hrs from being sown.  Good use for something that'd sit in a landfill otherwise and likely will outlive me, plus seems to do the job better than the cardboard I used previously (which will now be used in a new terrace bed out back).  Win-win!    My Vivosun mats are on a shelf in a 55 degree basement but with the Styro beneath they seem to do the job.   Now I just need to keep the seeds alive until transplanting time.

I was talking to my father about the issue today and he recommended I try Styrofoam as well. I think I will try that next! Wow, 72 hours! That's what I was expecting out of the heat mat. Do you use the thermostat as well? Do you know how warm the mat is getting your soil?

hi, i bought the vivosun heating mats without thermostat for 11.99. they heat up in about an hour. the temp can vary due to the room temp, but most of the time it is between 70 and 75f. if there is a hot day, the temp will read in the 80's and i might remove the trays depending on what i am germinating. i use a separate small standing digital thermometer and set it either on the mat or on the soil in a cell in a tray to check the temp. most things want a temp of 70 to 75 anyway and so for things like peppers and red malabar spinach, i put them near our wood stove with a thermometer on the soilless mix until the seedlings emerge and then to the mat. i think if i bought a heat mat and it was listed as heating to 90 degrees and it did not, i would want to return it as it is not doing what i expected of it. however, i really do not think you need mats with a control as they are more expensive, but since you only are using one the price does not seem as important and you should get what you paid for. your tomatoes and other things will still germinate, just maybe a bit slower. other than peppers and tomatoes, anything over 75 would probably be too high anyway. just my opinion

I may be off, but I was wondering about using a dome over top.  Heat rises, and it just seems like the moisture dome helps keep the heat where it should be instead of drifting away.  I got a heat mat last year, from what I can see it looks like yours. I didn't get a thermometer.  I did have a humidity dome on, and assumed it was working because the moisture was accumulating on the dome.  I did have cardboard under the mat because I had it on my dinning room table, and didn't want to damage the table. To be honest it never even occurred to me to check the temp.  It's always a challenge learning a new skill. I consider myself a beginner as starting seeds indoors, and I have had some lovely successes, and  some epic failures.
Good luck to you.

So I found a decent chunk of Styrofoam and set my mat under that. It seems to be heating much better now. However, Vivosun has great customer service and sent me another one, so I guess I will have 2! Even though it is working better, I still don't believe it was working as well as it should be. I want to be able to heat in my garage when it is colder so hopefully this new mat will allow me to do it next year. It seems as though the controller/thermostat is meant to keep the mat from getting too hot, as people complain that without the thermostat it has fried their seeds. Obviously I'm not having this problem

Thank you all for you input, I am probably overthinking things and going a little bit overboard, but I'm so stoked on starting to harvest and plant my seeds that I just want ALL the things!

I will absolutely try and find some sort of dome too. I know they have some domed seed cells on Amazon that I might try.  

I'm using a "Heated Pet Mat" we've had for years and it was running a bit too cool to get the job done. It specifically states not to put it on anything flammable, (including furniture), so I finally decided the safest place would be the "artificial rock" countertop in the bathroom. I also put a bit of electric heat on in there *and* put a plastic bag held up with some bamboo bits over it and finally at the top of the soil I'm getting 72 F most of the time, and my tomatoes and a couple of other heat-loving plants germinated in response.

Do folks turn off the heat mat once the seeds sprout?

This was one of the things I learned the hard way.  The seeds need to be removed from the mat as soon as they germinate.  I read this after I had seeded  a 72 cell tray of a bunch of different seeds.  If the seedlings are left on the mat they grow to fast and can get spindly.  Tomatoes are no big deal, I just planted them deep when I repotted them.  I had a few other veggies I  tossed to the chickens, and started over.  
Now I cut the cells in sections of 6 and plant like seed's together. Then if the tomatoes pop up I remove them  and can leave the peppers.   You get the idea.  Lesson learned.

Jen Fulkerson wrote:This was one of the things I learned the hard way.  The seeds need to be removed from the mat as soon as they germinate.  I read this after I had seeded  a 72 cell tray of a bunch of different seeds.  If the seedlings are left on the mat they grow to fast and can get spindly.  Tomatoes are no big deal, I just planted them deep when I repotted them.  I had a few other veggies I  tossed to the chickens, and started over.  
Now I cut the cells in sections of 6 and plant like seed's together. Then if the tomatoes pop up I remove them  and can leave the peppers.   You get the idea.  Lesson learned.

Thanks for this info Jen, this was actually my next question! So by germinate, do you mean as soon as I start to see green? Or after they have popped up a bit? I've noticed my tomatoes are a bit thin and spindly, but I've never grown from seeds before, so I have nothing to compare it to. I've attached photos of my romas and some cucumbers. I took them off the mat just now, hopefully it wasn't too late, especially since the mat wasn't getting super hot.

My heat mat's in a warm room of the house, but my grow lights are by a big window so that I can use natural light when it's sunny. So I definitely move the germinated seeds as soon as they show their cotyledons. However, I start my seeds in individual paper pots, so I can move them one at a time and not worry about the whole group being up.

As soon as the seedlings pop out of the soil you want to give them as much light as you can.  Ideally 12 to 18 hours of light, and 8 hours of dark.  
Cotyledons are the first leaves on your veggies. The second set are the true leaves. When the seedlings have a set of true leaves you need to give it some sort of nutrition. There are many options on what you should do.  I try to re-pot them in a good organic soil mixed with organic compost.  Some use compost tea, some fish emulsion, etc. What ever you decide to use make sure to dilute by half with water.  
Your tomatoes don't look to leggy to me.  Everytime I re-pot, or plant my tomatoes I remove some of the bottom leaves, and plant them deep. Tomatoes are amazing, if the stem touches soil, it will grow roots.  I was hardening off a tomato plant, and it fell and snapped it in half. I recut both ends, and stuck the top in some soil, and it's growing.
I have read if you have leggy cucumbers you can plant them up to the first leaves. I have not done this myself, so maybe try it with one or two to see if it works. You can't do it with all plants.  Like peppers will rot is you re pot them deeper than soil level.
To be honest I have had leggy seedlings like your cucumber do great, and some not make it. So we'll cross our fingers and hope for the best.
When you are ready to plant your baby veggies outside you have to harden them off.  I always thought that meant getting them used to the weather, but it's really all about the sun.  The typical way is to put them outside for an hour or two in the morning, bring them back inside the next day double that etc, etc, until they are out all day then you can plant them.  Or three days in a row of cloudy overcast days. It's how you can adapt them to the Sun without getting sunburned.
Good luck, I hope everything grows well for you.

Most seed starting heat mats don't go over 80 because you'll fry your seeds. 90 degrees is way to hot, even for tomatoes and peppers. I have several seeds mats and one does get hot but I have terrible germination due to the excessive heat. My book, written exclusively about seed germination and seed saving, indicates most seeds germinate best at temps in the mid 70s.

Get a good LED light for your seedlings and they won't get spindly. Hang it around 6 inches from your seedlings and set it on a timer so they get around 12 hours of light. Also, be sure to water from the bottom so you don't end up with fungus and damping off problems.

I've made every mistake possible in the learning curve.  Most of us have so just keep working at it.  Saving seeds is a bit tricky so it is worth every penny to invest in a good book. Some plants have unique tricks to end up with viable seed.  You don't want to bet the farm on your seeds and end up next year with nothing growing!

"The New Seed-Starters Handbook" by Nancy Bubel is excellent. It's nearly an inch thick and covers seed starting from start to finish for fruits and veggies, herbs, flowers, trees, bushes. Worth it's weight in gold! Hope this helps!

I wasn't extremely clear in my earlier posts; I'm trying to get my soil no higher than 80 degrees. I set my thermostat to 90 in an attempt to keep my mat heating in order to get it to 80. After getting tit to the right spot and proper insulation,  it's keeping around 75 which is just fine by me. Before it was only heating to about 2 degrees above room temp (67).

As far as grow lights, if I can get the germinated seedlings to a sunny windowsill, will that work? Or should I just invest in a light? If the seedlings are some natural light AND grow light UV's, will that be bad? I will absolutely check out those books! Is the one you authored under your name?

Evan Kruschke wrote: As far as grow lights, if I can get the germinated seedlings to a sunny windowsill, will that work? Or should I just invest in a light? If the seedlings are some natural light AND grow light UV's, will that be bad?

From the address you've posted and the fact that it's early April, I'm not convinced that even on a sunny window ledge, the plants will get enough "hours" of light for good growth. I don't know your weather pattern enough to guess your percentage of "sunny days" vs "cloudy days" vs "constantly changing".

I like my plants to get some "real sun", so we set up a pair of double fixtures that used to be fluorescent, but are now special LED grow lights. The original one is on a pulley system so if the sun shines, I pull the cord and it raises to the top of the window to let the sun hit the plants. It also allows me to adjust the height as the plants grow. The second system is much simpler to build - we used the type of chain you can salvage from swing-set swings (or buy at many Hardware stores) and a pair of breaching snaps. To raise it, I put a link of chain close to the light hooked through the snap on that side, and then repeat the process on the other side. As the plants grow, I can alter the top of the chain by however many links will set the light so it can't have an accident and squish everything.

The lights are on a timer which adds extra light in the morning, and again in the evening, with a gap in the middle for natural light. Unfortunately, the system breaks down when the Big Leaf Maples leaf out and significantly filter the sunshine to that window. None of our other south-facing windows are wide enough to take a four-foot fixture - how thoughtless of the original builders! ( Just joking!)

I'm a cheapskate, so I put my minigreenhouse on top of the fridge and another on top of the hot water heater. That does the trick for me; 24 hours a day of warmth but not outrageous heat. And when they germinate, then they go in the south facing window. I never have germination problems (except with weird exotic seeds, tropical stuff or things that need to be stratified).