The Wonders of a Heat Mat! (for Early Seed Starting)

The Wonders of a Heat Mat! (for Early Seed Starting)

This year I invested some money into heat mat.  I’ve heard for years how bottom heat speeds up seedling and root growth and I thought it was high time I got my act in gear.  So toward the end of last year I ordered one. And let me say, I’m enjoying it already!  It’s not really time to start seeds, at least for the vegetable garden which is where I start most of my seeds, but I wanted to test it out. I needed to figure out the heat mat’s idiosyncrasies before heading into full out seedling production mode.

Here’s what I’ve learned about my heat mat:

  1. Germination time increases greatly!  Instead of 7-14 days on spinach I found that the seeds germinated in less than 5 days.  By knowing this I can adjust my seed starting schedule a little.
  2. The heat mat can dry plants out much faster.  It makes sense doesn’t it? Increased heat increased the rate of evaporation. I discovered this fact when we left home for a few days over Christmas.  I left the cover off of a flat of seedlings that included kale and chard.  When we returned many of the seedlings has dried out and died.  To fix this covers of appropriate heights should be used to keep the moisture inside.  Or just check the flats daily!
  3. Growing heucheras from seed is still fun!  I’ve grown heucheras from seed before but this time I used the heat mat to get an earlier start.  The seeds came from 2010 and were a mix of various types.  ‘Palace Purple’ comes true from seed but most of the other varieties do not.  That’s good because I want some different unique heucheras to emerge from this crop of seedlings.
  4. Keeping a lid over the flats greatly increases the amount of heat retained in each flat, which means the heat mat doesn’t have to work quite as hard to maintain a good temperature.
  5. Damping off can be an issue!  This happens without the heat mat as well.  Damping off is an annoying fungus that loves to destroy tiny seedlings before they have had a chance to really get going.  If you can combat the fungus long enough for the seedlings to grow strong you can resist it.  I’ve used the Safer Brand fungicidal soap in the past which has done a good job at keeping damping off at bay.  Another method you might try is a mixture of baking soda (2-3 TBS), water (1 Gallon), horticultural oil (2 TBS) and liquid dish soap(1/2 tsp). 
  6. Heat mats make seed starting more versatile!  What do I mean by versatile?  Before the heat mat I was doing my seed starting in a walk-in closet with central heat.  Now I’m doing my seeds in the garage!  By using the thermostat I bought with the heat mat I can keep the seedlings at a constant temperature even when it’s in the 30’s outside!
  7. Heat mats make gardening more fun!  Pure opinion here but I think you’ll agree!

Spinach seedlings

I bought the large size mat which is 20″ x 48″.  Currently I’m working on building a structure that will be a heat mat table with an enclosure to keep moisture and heat inside as well as a light stand to hold a 48″ grow light.  Lighting is extremely important.  Natural lighting is best but when you are working in a garage you don’t really have that option.  You can see from my young spinach seedlings that more light is needed. Leggy seedlings mean you need more light.  Currently one tiny light is supplementing the natural light.  Once I get my seedling propagation chamber put together I shouldn’t have this issue.  It’s best to keep the grow light within a few inches of the tops of the seedlings for optimal growth!    

Heuchera Seedlings
Have you ever grown seedlings with a heat mat? 

You can find heat mats and thermostats at these online stores:


Dave has written since 2007. He gardens on an acre and a half where he raises his 4 children. He enjoys growing vegetables, herbs, and propagating plants. Dave has a side business growing and selling heirloom vegetables and herb plants through Blue Shed Gardens and works as a real estate agent in Spring Hill, TN.

This Post Has 6 Comments

  1. I have not. Have always been curious about them though. Thanks for sharing your experience thus far. I am really curious to know how much faster bell peppers will germinate.

    1. Darla,

      That's a good question! I'll find out in late February. Peppers do seem notoriously slow to get going.

  2. I just ordered heating mats and am impatiently watching their tracking info. This is the first year I'm trying to start my own seeds inside and the only place I can do this is in my garden shed, which is not heated. Thanks for all the tips- I will be needing them! Do you take your seedlings off the heating mat after they have germinated? I was wondering if that would help their growth or just cause problems with drying out.

    1. Julie,

      I did the same when awaiting my heat mats! So far I've just left the seedlings on the heat mat. The garage can get fairly cold which isn't a good thing until the cold tolerant seedlings can be hardened off. I'm going to be enclosing the area which should slow the drying out process and should speed their growth. Heat mats are also good for speeding the rooting of cuttings.

  3. Seedlings already? You are SO on the ball. I have a large heat mat and a small one. The small one quit working for some reason but the large one is holding on. We need all the heat we can get in this cold! Brrrrr! Did you soak your spinach seeds before planting? I just planted some and soaked them first. Wondering if they'll germinate. I should know in a week or two.

    1. I wouldn't call myself on the ball! Just testing at the moment to see how it works. I didn't soak, just sowed in the pots.

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