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Question about heat mats.

Hephzibah, GA

I use Park's Bio-Dome and lamps. I am thinking of purchasing heat mats. I need help deciding since they are so expensive. Are they worth it? How many years will they last (with good care)?
Thanks for any feedback

Ottawa, KS(Zone 5b)

I have several heat mats and have used them every year since 2006. I have no idea how long they will last, but so far, so good. Since I use them on chrome wire shelving, I put a layer of corrugated cardboard under them to serve as insulation and keep the wire shelves from impressing on them. I clean them gently from time to time with wet paper towels.

Some people say you don't need them, and that may be true. You will get some heat accumulation under your domes from the lights. I think I get faster germination of my zinnia seeds by using the mats. I also have thermostats for my mats, and I set them at about 80 degrees. But my seed germination is in an unheated basement utility room.

I said unheated, but it does get some heat from a hot water tank and the uninsulated ducting of a central heating propane furnace and, of course, from my 32-watt T8 fluorescent light bulbs, and maybe a little heat from the heat mats. Heat mats are generally rather low wattage. You might want to use some kind of thermometer (possibly a cooking thermometer that you already have) to measure the temperature of your seed germinating medium in your biodomes when your lights have been on for a while. If it is already 80 degrees or so, you probably don't need heating mats.

Needless to say, those are just my opinions. The subject of heating mats is somewhat controversial.


Columbus, OH

It is controversial, but I'm a believer. I get much better germination with heating mats, so I use them.

Galesburg, IL

First, get a good soil thermometer and record what your temperatures are in your planting media - do this several times throughout the day. If your temperatures don't get above about 65 degrees, you would probably benefit from heat mats depending on what you are germinating.

If you plan on using heat mats, I would highly recommend using a thermostat with them. I won't use mine without one. Heat mats are designed to raise soil temps from 10-20 degrees above ambient and they will cook seeds if your ambient temps rise a little higher than you think.

I only use heat mats for quick germination. Once seeds have emerged, the plants get moved off the mats to cooler temps.

Oak Island, NC(Zone 8a)

I actually prefer soil cables instead of the heat mat because they are so much cheaper than a heat mat. I built a frame out of wood with some window screening stretched and stapled inside the frame. I then spread a thin layer of contractor grade (it's very course) sand on top of the screening, loop the cables on top of the first layer of sand, and then I put another layer of sand on top of the cables. The frame, sand, and cables sits atop of two sawhorses. I then sit my plantings in their flats or pots on top of the sand. This way water can drain away from the seedlings and I don't have to worry about them becoming waterlogged or getting over watered.

Some seeds like heirloom tomatoes must have bottom heat to prevent stretching spindly pants. However, some plants/seedlings like lettuce don't do as well with bottom source heat. It depends on what you are growning. I suggest doing a google search or here on DG to see if the the seeds you are trying to grow require bottom heat.

But yes, bottom heat works wonders on some plants.

Columbus, OH

Some plants just germinate in warmer temps. Lettuce would probably go to seed after it gets two sets of true leaves, but tomatoes and peppers do so much better for me with bottom heat.

Casper, WY(Zone 4a)

You can get enough botom heat by placing the planted seed on top of your fridge or tv.

Foxboro, MA

You will get germination at lower/ambient temperatures for most seeds without a seed starting mat. It all depends on your house and climate. We kept our house very cold (55-60F) this winter until we can convert our heating system and insulate the house (90 years old). I knew that this was not going to be conducive to seed starting. I have one true heating mat that I use for the fussiest plants (all of my husband's hot peppers) and 2 home made seed starting mats that made following this technique. The DIY mat ended up being about 10-12 degrees above ambient temperature which is plenty for most seeds. Since I am starting so many seeds I end up rotating the pots. As soon as one seed sprouts it is moved off the mat and another is put in its place. Some of the less fussy (or critical) plants have been started without a heating mat (i.e. my herbs). HTH.

Iowa Park, TX(Zone 7b)

Microbiology1 I have a question for you about starting peppers from seed. Should I start another thread or can I ask it here?

Galesburg, IL

I would suggest starting a new thread so others can see it and possibly respond and offer help as well. I also grow many different varieties of hot peppers and wouldn't have seen your post except for the fact that I responded to the OP and am watching this thread.

Jonesville, SC(Zone 7b)

I bought my heat mat from Harris several years ago. Knock on wood, it is still going strong. I am a firm believer because I can control the soil temp and I get great germination. I would not attempt to start them any other way. I also built a set of lights; stand, lights, chains, etc. If you build your own, you save a lot of money! However, I did buy a double decker light stand from Harris as well but it did cost a good amount of money for me.
I can briefly describe germinating peppers--they take longer than tomatoes, they grow slower than tomatoes, cover the seeds with about 2-3mm of soil, water them in, put them on the heat mat at 80 degrees, then wait. I don't know if I answered your question without seeing it. I did make an attempt though.

Calgary, AB(Zone 3b)

Studies on seed germination by Henry M. Cathey and by Dr. Norm Deno indicate that bottom heat and temperatures above 70 deg F ("room temperature") show no benefit, including for the common garden vegetables and annuals for which heat mats are usually recommended. Two situations were found where temperatures above 70 were beneficial - for fresh Gomphrena seed, where unusually high (85-95 deg F) temp was beneficial; note though that this tendency was lost with dry storage of the seed); and for Passiflora where temperatures above 70 were reported to be beneficial (Deno says that he has not tested this himself).

So, unless you germinate seeds in a cold greenhouse, very cold basement, or some other situation where temperatures are much less than 70 (say down to 50), scientific study does not support that there is any need for heat mats, or any benefit from them.

So, I know a lot of people "like" using heat mats, and indeed they are useful if you are starting seeds in cold conditions, but if you are wondering if they are necessary or even beneficial otherwise, well, there it is.

Everett, WA(Zone 8a)

My house doesn't get up to 70 until summer. I usually keep it around 57 when Im away (all day weekdays) and while asleep. If moist soil evaporates at all around the humidity dome or plastic film, it is probably a few degrees (2-5 F?) cooler than that.

I usually dial the house thermostat setpoint up to 60F or sometimes 62 when I get home, and back down to 57 to sleep. But I suspect the soil in the trays never warms "all the way up" to 60.

I think many seeds germinate faster at 75 F than 55F. But maybe my heat mat is only bringing my soil temp UP to 70, and this is a long-way-around, indirect way of agreeing with you!

As to there being a benefit or not between 70 and 75-85, for tomatoes and peppers, I don't know.

Did Dr. Deno's study consider it a benefit if germination was faster, but no higher percentage was achieved?

>> including for the common garden vegetables

Even tomatoes and peppers? That does surprise me. Johnnies Seeds shows optimum germination temp for them both as 86F, and I really respect Johnnies practicality. Flipping through their catalog randomly, I see optimum germination temps mostly at 77 or 86, and did not spot any optimums at 70F. They're based in Maine, so maybe they have a pre-occupation with warmer soil. :-)

Tom Clothier lists % germination and days to emergence against temperature, and the "days to emergence" is shorter at 77F than 68F for most of what he listed:

Maybe Dr. Deno maintained perfect conditions other than temperature for his test, but many of us have too-moist soil, or poorly-aerated soil, or less-than-sterile soil. If so, we would benefit more than he did in that test, from having seeds emerge 5-10 days sooner. Less chance of rot, and I am guessing that a seed that emerges 5-10 days sooner has more reserves and vigor to fight off things like damping off.

I'm just speculating. But that might explain the difference between a controlled-test result in a lab setting and he very widespread belief among gardeners and farmers that seeds germinate faster at higher soil temperatures, up to the optimum temperature for that species or variety. Or maybe many gardeners keep their houes colder than 70F in winter and early spring!

P.S. Many sources remind us to remove emerged seedlings from heat ASAP, because many plants develop better (more stocky) if grown on in cooler conditions than those for optimal germination.

This message was edited Apr 3, 2012 7:48 PM

Ottawa, KS(Zone 5b)

Hi Corey,

"Did Dr. Deno's study consider it a benefit if germination was faster, but no higher percentage was achieved? "

I don't know about Dr. Deno, but I consider faster germination as a benefit. I use thermostatically controlled heat mats to get faster germination. I feel that the longer a seed takes to germinate, the more danger it is in from attack by soil-borne or seed-borne organisms. And the quicker the seed comes up, the faster it can develop as a plant.


Galesburg, IL

ZM, I think Deno was only concerned with germination, he was a chemistry professor who started those studies looking at the chemistry and physiology of seed dormancy/germination and I'm sure he didn't monitor plant growth (unless he wanted to use some of them for his own landscaping ; ).

I agree wholeheartedly with your opinion on rapid germination, it can prevent many problems from occurring. Faster germination limits the ability (narrows the window of opportunity) for pathogens and insects to damage seeds.

Everett, WA(Zone 8a)

>> I think Deno ... was a chemistry professor

OOOHHH!!! I always wondered why he did germination experiments with fewer than 20 seeds. I guess, to him, if one test tube turned blue you would expect most of them to turn blue, so germinatining 12 seeds seemed like plenty of replicates.

His book about germinating difficult plants ("Seed Germination, Theory And Practice") is available free online, and it is great.

Persistent URLs for Dr. Deno's book at AgSpace :
"Seed Germination, Theory And Practice" and supplements: (1993) (1996) (1998)

Those are permanent links to reach specific documents at this website, which has a TON of free publications:

National Agricultural Library (NAL)
NAL Digital Repository
Digital Documents Repository (DDR)
"AgSpace": a centralized location for USDA publications

Other Agricultural Collections
Other Agricultural Research and Information

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