How to Use Heat Mats for Seeds (Spider Farmer Heat Mat Kit)

Seedling heat mats can make a big difference when starting seeds, especially for plants like peppers and tomatoes. Gardener Scott explains how heat mats work and how to use them for seed starting. (Video #420)
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[@joeshmoe7789]

For the super hot, extra small chile peppers, I start mine in June or July for the next season here in NJ. I bring them inside for the winter and in the spring, the sickly looking plants start to produce small green leaves. I don't leave them outside until mid to late spring or when they're strong and healthy. I get tremendous growth and production immediately and have red pods before the 4th of July, then bring them back inside in September.

[@garynorcal4269]

Great timing for me .. I got a heat mat last year. I started my 1st set of seeds for this year last week. I set up my indoor starting area and am prepared to grow up to about 200+ plants before moving them outside. And, I am prepared to sequence start these plants at about 36 plants at a time and then keep them on 4 different shelves depending on how tall they are .. 3 of the 4 shelves have height adjustable grow lights. I wish all of you other gardeners as much success with your gardening as mine appears to be having on my 1st planting for 2023.

[@noraalvarado8178]

Great technical video as always. I don't even own a heat mat. And I grow my whole garden from seeds. I use my furnace room. Any seed that needs a heat mat I put right ontop of my hot water holding tank with the plastic cover or glad wrap. I check on them twice a day. As soon as I see germination they go right under my grow lights with the plastic off. I have germinated seeds also by laying bags of potting soil on my concrete. By cutting out one side to plant and the other side sticking a screw driver in it for drainage holes. And then put a clear plastic tote ontop. As soon as it warms up the seeds germinate depending on the plant. I also start my sweet potatoe slips in my furnace room using the soil method. And I get so many slips. Last year I got over 80 and gave some away. Sweet potatoes love the heat. The water method is to cold and takes way longer.

[@pat_in_va8605]

Thank you for stressing the importance of removing the heat mat once the seeds have germinated. I, too, learned this the hard way.

[@chompers11]

I have 12 seedling trays. What % germinated would you remove it at? I have 2 out of 12 popped and I'm curious if I should wait or not

[@bonniebon7335]

Thanks Scott. Best stress free gardening channel.

[@TalkingThreadsMedia]

We keep our house at 67F. That is too chilly for proofing yeast when making bread. The temperature-controlled heat mats do double duty. Thanks for all the great info. Best wishes from Kate in Olympia, WA - 1/23/2023.

[@chompers11]

I'm real close up the 101 and always frustrated with bread haha! Interesting. When do you think last frost will be

[@TalkingThreadsMedia]

Hi, Ri. The last frost date in our area usually falls between April 17 and May 9. Hope this helps. Happy gardening! Best wishes from Kate in Olympia, WA - 3/26/2023.

[@chompers11]

@@TalkingThreadsMedia yea I'm feeling like it's going to be on the back end of that time frame this year

[@TalkingThreadsMedia]

I think you are right... I’m guaging my seedlings closer to the May 9 timeframe. Kate

[@brianseybert2189]

Completely agree with having a thermostat with the heat mat. I keep the soil at 75F for peppers and tomatoes. Sweet potato slips generate quicker on a heat mat as well. Great info on heat mats!!!

[@cindynielson4231]

I have used a heat mat in the past but didn't realize to remove it after germination. I also use the humidity domes. Thanks for sharing your wonderful knowledge. 👍

[@ScottHead]

Great info Scott. I got a variable temp heat mat last year with the thermometer probe and it made a big difference.

[@dustyflats3832]

I love using my temp controlled mat. The sprouts jump right up. Interesting fact about celery. I also read that celery can bolt if subject to too cold of temps at transplant-who would have thought? Good job!

[@Gardeningchristine]

I bought some celery seeds, and there were 700 seeds in the pack, and they’re so small, so I thought they must have a low germ rate. Boy was I wrong. I seeded about 10 in each cell and now I have 50 celery seedlings. I’m not complaining, it was just a surprise. If they all make it I can give some away.

[@jamessanders4310]

My tomatoes are about 4' tall and bursting w flower buds. My, what a difference a few growing zones make. I'm in zone 9, SW Florida. Planted lettuce, radishes, cilantro yesterday. Going to plant jalapeño tomorrow. Strawberries are coming on very nicely. You guys up Nawrh are months away us.

[@YoPaulie21]

Thank you for the video. My heat mat doesn't have a thermostat and I find it does heat the soil a bit too much. My solution was to use an appliance timer to cycle the mat on and off. Definitely good advice to check the soil temperature.

[@bevbarry9637]

How long was your on cycle and off cycle please?

[@YoPaulie21]

@@bevbarry9637 You may need to experiment a bit and it depends how many on/off settings your timer has. I found 1 hour on, 1/2 hour off worked well. I'd advise checking the soil temperature after 24 hours to make sure.

[@bevbarry9637]

@@YoPaulie21 Thank you.

[@heidiclark6612]

Thank You for always explaining the details. I love my heat mats. I just started using a thermostat last year and it has made a difference.

[@amymorales4622]

Thank you for this. I am hoping to get some hot pepper plants to sprout using heat mats, and this information will certainly help.

[@FrozEnbyWolf150]

I don't have any heat mats, but I do have other options. My grow shelf is in front of a south-facing window, which is right above the radiator. If I need a warmer environment, I use the wet paper towel germination method over the oven pilot light. Most seeds germinate pretty quickly, assuming nothing else goes wrong. I'm going to try the latter method for my superhot pepper seeds this year.

[@barrycurran1985]

This video was Just in time my Friend, I just got a heat mat for Christmas... Thanks for always giving us the most timely and accurate Gardening info.

[@benmabebajr.6551]

Great info particularly for soil temperature (seed germination). Well appreciated 🙏🏾

[@poodledaddles1091]

Started onion seeds and celery seeds approx 1 week ago. The onions are sparse the celery is massive and looks almost sprouts to eat. I used the heat mat on both. Thanks for the video!

[@daveclark1904]

Great info Scott, thanks! This totally makes sense why some of my seeds in the past either never started growing or took forever to sprout! Now that we live in Colorado I'm still trying to adjust and figure it all out!

[@ronthornton2583]

Also great for curing sweet potatoes 🙂🙂

[@brianseybert2189]

I do the same thing with my sweet potatoes. Made a screen to go over my large heat mat, place a pan of water and cover with a light painters plastic drop cloth. Potatoes done in a couple weeks, super sweet.

[@GardenerScott]

Absolutely. It can be hard to get the right heat and humidity for curing and mats are great.

[@OShaughnessysPub]

Beginner Rookie gardner here!!!😃 i know nothing and just wanted to plant some spinach seeds inside in December to see what would happen, according to Gardner Scott I did everything wrong i.e. used my human heating pad for sore muscles(walgreens) then I used grow lights for only 12 hours a day and used good old fashioned egg cartons ( because thats what i had) then i kept room temp at 55 degree’s… I had great success surprisingly enough😊PLEASE Dont get me wrong, I love learning everything Gardner Scott teaches us, I am just hoping everyone will try to grow something even if they dont have all the fancy gadgets and all the knowledge!

[@justinp4996]

Informative as always! I have been a home gardener for 20 years and today bought my first heat mat to try out with germination times.

[@BearBottomHomestead]

Great information Scott, thanks for sharing!

[@cherylhowker1792]

I have looked at the heat mats but they can be a bit expensive for my budget. I do have a propagation system that is an all in one unit and heats up to 10c about room temp. Again like you say it can be hit and miss as don’t have any way to adjust it except to open air vent to cool it down a bit. But last year everything I put in it germinated and then I either turned it off and left the lid on to help the plants grow a bit or took the lid off . But I will say my heating radiator is under the window sill and the propagate is on the window sill so I think that helps.

[@Josef_R]

I just spent the last few months killing plants in my grow room. I was trying to start brassicas but I was using a heat mat. The few that would sprout got leggy, the soil stayed crunchy, and the plants kept shriveling up like my LEDs were burning them. I kept moving my lights up and down, between leggy and burnt, I couldn't figure out the height. Turns out, it was probably the heat mat I never turned off and didn't need at all. I got nothing at all planted this winter and wasted hundreds of seeds. I have new trays going now off the heat and dome covered. Also have my spring stuff on heat and covered. Also shut off the vent in that room because I keep the house at 72, it was pretty hot in there.

[@brianseybert2189]

We all have made the same, or similar mistakes. Your not born knowing this stuff. Don't give up!!!

[@Josef_R]

@@brianseybert2189 What made it worse was that it froze to 18 degrees here (never seen that low in my life, usually 30) and killed everything I planted all year that wasn't in the greenhouse. 100s of really nice plants I had been growing for months and two new citrus trees. Stuff in the grow room could have replaced it if anything had grown.

[@johnjude2685]

@@brianseybert2189 Agree we all are born knowing nothing then some of us learn

[@LeverActionLarry]

Im hoping the two 4 footer heat mats I got are enough to bring the soil / ambient temp up on my custom insulated grow rack. Garage is at 43°F, we'll see! I am also looking into a small oil filled heater. Thanks as always GS!

[@Mywalkingblog]

Weird happenings in my seed starting tray this season, every one of my tomato(carbon, paul robeson, dark cherry) and tomatillo(queen of malinalco) seeds germinated yet zero of my peppers(golden treasure, buran) or ground cherries(aunt molly) germinated. All in the same tray. So, my next step is to get a heating mat like what you detailed in this video.

[@solidsnake6512]

Peppers generally like to be frozen before germination, in case that helps.

[@ThePattiable]

I needed this video this weekend!

[@yibuseato]

Thank you Gardener Scott! 🌱

[@rachelsweets]

Great information thank you

[@vancevandernoord8363]

Had negative effects with heat mats here in Australia. Room temp generally range from 15-20c. Under led lights with humidity domes work amazing for me. Nearly all seeds pop. Peppers take around 3 weeks but all pop.

[@brad4527]

Scott thanks you for the information. I will probably keep my heating mat at 65* being , I only keep the heat at 60* degrees when we're not home. So I will definitely keep your video in mind, would you suggest anything different? I'm doing my tomatoes ,sun flowers and some other flowers . Thanks Scott. Brad. NJ zone 6b

[@joanies6778]

Great info. Last year I broke down and bought a heating mat for the first time. It has variable temps, but they're not marked. I think I burned my first trays of seeds by having it too high, which cost me several weeks prpduction because I had to start over. Then I thought about using my kitchen instant read thermometer to check and monitor soil temps on the second + batches, which were successful. Just goes to show the extra bucks for a heat mat with more whistles and bells is worth its weight on gold. However, I was not aware once they sprouted, I needed to take them off the heat. (Just recently learned it elsewhere. ) This time I plan to moisten the seed starter first, get the temp set, then plant my seeds. Or maybe also get a better heat mat. 🤔

[@sandi9546]

Thank you. Very helpful info.

[@sylviaprudhomme5417]

Dry informative😊😊😊

[@loriirons9503]

Thank you for this information! It is greatly appreciated!

[@davidpatrick1813]

I will check out the unit. Watts and Amps are important to me as I am trying to be using solar as much as possible

[@Tyler-eo2li]

Scott I have got to be honest with you, I have been so successful with using just a heating pad they work the same way just take the fabric cover off and set it on the low/medium setting. I am undefeated with this method!!!! Great video but honestly I am proof that your theory is incorrect… yes a normal heating pad will work just as good… consider the mechanics of the device they work identically…. Take care Scott !

[@Gimme_Cornbread]

Super helpful!

[@jasons-jungle]

I just use a couple of dumb propagators with no thermostats. As my growtent is now plugged into my home automation system which includes smart plug sockets I'm just waiting for a couple of smart soil temerature probes to arrive so that i can then have the propagators turn on and off when they hit certain min/max temperatures and also tie them into my grow lights if i need different spil temperatures during the day and the night. I can get hotspots on the propagators which can mean that some cells in a modular tray dry out faster; using a layer of damp soil or soaked capillary matting means that the water transfers the heat around and evens the temperature out to prevent this.

[@milkweed7678]

Wow, great info I never thought about before. Where did you get that little red soil thermometer? Didn't find it on your site anywhere. Thanks!

[@GardenerScott]

It's actually just a kitchen meat thermometer.

[@CigarShark]

Super helpful dankeschon

[@GardenerScott]

Bitte Schon.

[@kitrussell9358]

Great video, but I didn't see link to ca.U. On temps?

[@GardenerScott]

Thanks. It was in the description. Here it is again: sacmg.ucanr.edu/files/164220.pdf

[@rickytorres9089]

Some seeds like MOST strawberries actually DO requires them so I had to order one and right sized pots for them too last minute. Also, Unless the seeds' requires it, it can get too hot and humid with both a dome and heating mat so be CAREFUL if you gonna combine those. So might be best to go with one of the other in accordance of what best for those seeds.

[@chrisfisher3900]

But starting seed on a heating pad could be the most electrifying type of gardening 🤷🏻‍♂️😂

[@sanchezable]

I’m looking for a what to hang my lights. What is that pulley system your using ?

[@GardenerScott]

They are ratchet hangers. I got them here: amzn.to/3Wz07CW

[@ejfishes7610]

I’m going to try a heat mat this season. For years, I placed my trays on top of the fridge in the basement, seemed to work fairly well but I like being able to control the temperature. Looks like your using a digital meat probe for the soil, correct? Thank you!

[@GardenerScott]

Yes, I use a standard meat probe as a soil thermometer.

[@lethaleefox6017]

Anyone know the wattage range of heat mats? Was thinking of bottom heat for cuttings, like boxwood.

[@GardenerScott]

All my mats are 20 watts. They should work fine for cuttings.

[@crazysquirrel9425]

I started tomato seeds yesterday. Today, with the heat mat and sunshine the soil temperature got to 100F. Are all my seeds dead now or can they take it for a few hours?

[@crazysquirrel9425]

Update: I since got one with a thermostat. Easier to control the heat level. However, for some reason the heat mat is not heating hot enough. I can barely reach 75F or roughly 5F above room temperature. Mat IS working though. Can you stack heat mats? Place one on top of another? I need 80F to 85F heat to start peppers.

[@bobcole3852]

What hand held digital thermometer do you use? We have the standard mats but tstat control is obviously better!

[@GardenerScott]

Here's the thermometer I use: amzn.to/3knwYgz

[@bobcole3852]

@@GardenerScott thank you, ordered one today!

[@BoltActionBob]

Has anyone tried to use this spider farmer thermostat with another heat mat?

[@jimrobinson7441]

Mine's not the spider farmer unit but it just has a 110v receptacle that the heat mat plugs into and also a temperature probe on a separate wire. Any 110v heating device could be plugged into it providing the load doesn't exceed the capacity of the thermostat (mine says 1000w max). Pretty sure the SF unit would be the same so yeah, any heat mat should work.

[@animalgirllover5421]

Do you have any tips for cloning my tomatoes

[@GardenerScott]

Here's my video on cloning tomatoes: kzbin.info/www/bejne/o5aUgomphtNlbZI

[@tomneal72]

Hi I have a rootit heat mat with thermostat and probe what I’m curious to know what temperature on thermostat is best for sweet peppers and I will be using coir pellets so where would the best place to place the probe ?

[@GardenerScott]

Peppers like at least 75F and 80F is better. Try putting the probe tip so it is in the middle of the pellet.

[@bevbarry9637]

Hi Scott. I have just ordered a cheap heat mat to trial it. I am currently using a mini greenhouse to germinate my seeds so there is a clear top/dome and a tray underneath for water. Will a heat mat work with this type of set up or do I need to start a new lot of seeds in a seed tray? Given the higher temperature you found with the mat without a thermostat do I still keep it turned on the whole time or should I turn it off for short periods of time so the soil doesn't get too hot? I am looking to have a soil temp around 20c or 68f. Thank you :)

[@GardenerScott]

It depends on the depth of the water. The water will absorb most of the heat before the soil, but it can help moderate the temp once it warms up. Keeping the heat mat on ensures the soil doesn't cool down and affect germination.

[@sugargraham6868]

Would this keep my roots warm on a bigger plant?

[@GardenerScott]

Yes, it would.

[@cynthiablanton9106]

Do you need to use grow lights when you are using the heat mat?

[@GardenerScott]

You don't need grow lights to germinate most seeds, but I like to have them in place so the seedlings have light as soon as they emerge.

[@cynthiablanton9106]

@@GardenerScott Thank you for your prompt response. I appreciate all your videos and the information that they provide. Have a blessed week.

[@brianramsey3824]

With no more than the number of seed u get in a pack if it improves germination it could theoretically pay for itself

[@rickthelian2215]

🖐🇦🇺

[@bustymaiden]

I have some shishito that i wanted to do straight into a 5 gallon. My god it has been 2-3 months to grow half a foot. I now have a proper cell tray setup instead of just tossing an oversized pot onto the heat mat.

[@JennySimon206]

Controlling the heat mats is getting annoying. I went out to the grow tent and my soil was 80something degrees. I might have lost those seeds overnight. Not good. Those are rare medicinal seeds arg. Can u do a video on how to set the temperature and make sure u don't screw up a flat of seeds? Should u do a test of the soil first? Should u put empty flats with just soil to even them out? Keep them completely covered?

[@GardenerScott]

I have had similar problems, which is why I like the thermostat and probe with the mat. I plan on making a video for pepper seeds that will include more heat mat discussion. Covering the tray can help keep it from drying out.

[@JennySimon206]

@@GardenerScott yeah I need to get a smart thermostat for inside the grow tent so I know how hot it is inside. I'm gonna order one right now actually. That might help. I think it was too hot in the tent and needed venting.

[@bonniecarlstrom6014]

👍👍🇺🇸

[@pattie3338]

Spider farmer is a horrible company. I know the purpose of your video is not what I am about to say but I have to say please don’t advertise for this company. I bought 4 of these mats based on your video (I love your videos by the way), and none of them worked and I’m going through a lot of pain to return them. They just ignore me. I never had such a horrible experience with any company. I feel like I’m talking to aliens 👽 on their website they advertise free returns but it’s just false. I explained over and over and took videos and pictures of the mats and they just ignore everything I say. I told them the mats won’t heat up, they responded back can you take a picture of the package, then I asked what does that have to do with anything then they said can you record a video showing the mats aren’t heated up??!!! 😂😂😂 like really?! How they felt the heat over the video beats the hell of me! They are in China somewhere and respond once over night. I’m on my 8th email with them 😢😢😢

[@GardenerScott]

Thank you for letting me know. I appreciate the feedback.