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Beginner's questions regarding heat mat

Posted by zaphod42 SE WI 5 (My Page) on
Sat, Feb 18, 12 at 9:31

I am going to try starting some plants from seed inside for the first time this spring. I'm good with the info I've found on light set-up, but am still a bit in the dark regarding the additional heat. My basement hovers around 60 degrees. I purchased a heat mat. Do I leave the heat on 24/7? If not, how many hours on and off? Do I need to measure temp? How long do the average plants need the extra heat? I only bought one mat and thought to rotate it as I stagger the seeds I'm starting over the spring. Also, I'm a bit paranoid about leaving things plugged in while unattended. Can I unplug when I leave the house? How safe are these elements? Thanks!


Follow-Up Postings:

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RE: Beginner's questions regarding heat mat

Heat mats are used for germination only. Once the seeds sprout and break the surface of the soil they must be removed from the heat mat or it will cook the roots.

But yes, 24/7. The heat must be on continuously until than happens. Turning it off and on just defeats the purpose of using it and the seeds may rot due to the extreme changes in temp.

60 degrees air temp equals approx. 50 degrees soil temp and nothing except some of the leafy greens will germinate at that temp.

Without the thermostat: The mat has a small built in thermometer that acts as safety shut off. It is made to give you approximately 10 degrees above the ambient room temp. But in large rooms that are that cool they will burn themselves out quickly trying to keep up with the room temp. It is trying to heat 'the whole room' and it just can't do that.

So you need to use a thermostat with it OR confine the area it has to respond to in some way. For example, see the post about Styrofoam and duct tape but any sort of small enclosure will work - even a plastic tent over the area. The thermostat allows you to control the exact soil temp.

Dave


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RE: Beginner's questions regarding heat mat

This is only my 3rd year with seeds under lights, however I havent used a heat mat at all and seem to get very good germination from my seed.

Because my grow shelves are built in to the wall, they are enclosed on 3 sides already. I hang a mylar reflective blanket (less than $3 in the camping section) over the front of the shelves and the lights have enough heat to easily raise the temp in there 10-15 degrees or more. The room I use is 60 degrees or less.

For seeds that like the soil exceptionally warm, 85 +,and dont need light to germinate, I lay the trays directly on top of the suspended lamps.

It is certainly possible that I would get even better germination with a heat mat, but I cant justify the price of the heat mats in relationship to the price of the seed, for 10% more germination.


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RE: Beginner's questions regarding heat mat

I am just a small hobby tomato grower. I find that a heat mat is not necessary but I use one sometime to speed thing up. If like digdirt says, you have a colder place you kind off need one. Being cheap, I get by without a thermostat. I have used a thermometer though. I place a starter tray on top on the heat mat. If it on metal, like a file cabinet, it runs cooler than on a wooden counter. If too hot a layer of thin cardboard between the mat and the trays slows it down. Like said, 24 hours a day until spurted, then get it off. Tomatoes do better if not too warm.


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RE: Beginner's questions regarding heat mat

I am REALLY new to starting indoors with seeds; but I learned quickly that I didn't need my heat mat. It really depends on how warm your lights are already getting your soil. With lights on and humidity dome on - my soil was HOT. I needed a fan unless I wanted to raise my lights.
In the end, I stil use my heat mat because I turn the lights off for a few hours each day (still haven't figured out why I do that - everyone just says I need to...:) ) . I keep the heat mat on the seeds that haven't germinated to keep the temperature consistent while the light is off. It took some tweeking because I needed to put my flat on chopsticks to raise it off the heat mat. Otherwise - my temp of the seedslings was still going to be too warm.
A digital meat / tea thermometer works well for me to see how things are going. Otherwise, it is a guessing game.


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RE: Beginner's questions regarding heat mat

Honnat - I was going to email you this but you don't have an email posted so will put it here in the hopes you'll see it.

With lights on and humidity dome on - my soil was HOT. I needed a fan unless I wanted to raise my lights. It really depends on how warm your lights are already getting your soil.

Then what kind of lights are you using? Fluorescent lights don't put out much heat at all - minimal. Even if they are very old fixtures with built in ballasts it isn't much and newer fixtures don't have ballasts in them. And it is top heat not bottom heat so it would be almost impossible for the lights alone to heat your soil to the very hot level. If in a very small confined space they can eventually WARM it but get it hot would be impossible. Lots of studies have been done on this issue and in over 40 years of growing from seed and measuring soil temps I have never seen any soil temps over 70-75 degrees from lights alone. Something else is going on here, there is some other source of heat causing your problems.

If you are using metal halide or HPS then yes they can produce sufficient heat.

digital meat / tea thermometer

Very different calibration on those. I would seriously question how accurate your thermometer is for measuring soil.

Also do you mean you are leaving seedlings under plastic cover? That's a big no-no.

Dave


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RE: Beginner's questions regarding heat mat

Check out my other post under this topic. Nothing wrong with my lights - just too much to have that close.
I do have my humidity dome still on - so far so good. Everything looks super healthy. I keep it open a crack and a fan on to keep some air moving around. I have many seeds that haven't germinated yet, so until they do, I think I'll keep it on (unless I start to notice damp off).

Here is a link that might be useful: Too Hot??


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RE: Beginner's questions regarding heat mat

Honnat: what kind of heat mat are you using?

FYI a humidity dome over anything other then seeds that have not germinated is a recipe for disaster. I love to learn by doing, so by all means keep going with what you are doing but please be aware that MANY of us have learned the hard way. and once you see damp off, there is nothing you can do but hopefully save the plants that have not shown ANY signs of the devastating disease.

Keriann~


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RE: Beginner's questions regarding heat mat

Nothing wrong with my lights - just too much to have that close.

No one said there is something wrong with your light but asked what type are they? Many here have extensive light set ups with no associated soil heating issues. Personally I run some 25-30 T5 and T8 fixtures in our commercial greenhouses as well as several metal halide and HPS units and there is minimal soil heating from them. We'd be happy to help you correct the issues you are having with more information.

But if you prefer to continue as is then please be aware that your findings and description of your issues is most unusual. So it isn't something one should encourage others to copy. There simply is far to much documented evidence to the contrary.

As Keriann said, a humidity dome over germinated plants - fan or no fan - is a recipe for disaster. Sadly some simply have to learn the lessons the hard way I guess. Good luck.

Dave


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RE: Beginner's questions regarding heat mat

Hi Dave.. just a question

Have you seen your HPS lights produce leggy plants because of their high red spectrum? Or do you use HPS for flowers/fruiting plants?

Thanks

Keriann~


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RE: Beginner's questions regarding heat mat

Yikes - i feel a little under attack here. Good to see you all care about my seeds so much (I guess...). I prefaced my advice in the first post with "I am REALLY new to this..." I wasn�t trying to lead anyone astray. The only advice that I wanted to give the original poster was that he/she may be getting enough heat from the lights and not need the mat. If I would have used a heat mat - I would have cooked my seeds in a hurry and my light set up is not that extensive (see link below). With lights and meat mat on � my soil temps were soaring over 100 degrees.

I realize keeping the humidity dome on is a bit unorthodox and places me at a higher risk for damp off. The seedlings are tiny and just now developing beyond the cotyledons. They look great so far. However, I think I'll follow your advice in the other thread and separate the cell packs of the two varieties that have germinated. Thanks!

Here is a link that might be useful: My light


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RE: Beginner's questions regarding heat mat

Honnat: what kind of mat were you using? or going to use?

Keriann~


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RE: Beginner's questions regarding heat mat

Please don't feel attacked. That isn't the intent at all and I'm sorry if you feel that way. We really are just trying to help anyone new to seed starting and save them from suffering the common failures that can be discouraging.

Dave


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Cool weather plants started on heat mat?

Should I start my cool weather seeds (snap peas, lettuce, greens) on a heat mat or not? I started snap peas and spinach already on the heat mats and only got 6/33 to germinate. Thanks.


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RE: Beginner's questions regarding heat mat

Depends on what setting is on your mat. All those will germinate fine without it as they want soil temps of only 55-65. If it is set too high - such as the temps required for peppers, tomatoes and such - they won't germinate at all well.

Dave


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RE: Beginner's questions regarding heat mat

Honat - thanks for the input, I love this kind of discussion. I do what works for me and love reading about everyones' methods and theories. For me mat and dome until sprouting then room temp under lights and fan.


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