The Best Seedling Heat Mats and Thermostats

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When starting seeds — no matter if you’re starting them for hydroponics or otherwise — it’s important to provide them the perfect germination conditions. Each type of seed has different conditions. But as a general rule, most seeds like to be in a growing medium that’s warm.

Because most of us are starting seeds indoors, either in preparation for the coming season or to grow them indoors, we don’t have the luxury of warm soil.

So, what to do? That’s where the almighty seedling heat mat comes into play. Before I got one of these, my germination times for almost anything I was growing were longer, and my germination percentage was also lower.

If you want to look at the products mentioned, here they are:

* For pricing and more info, see below.

Why Should You Germinate with a Plant Heat Mat?

Seed Germination and Soil Temperature
A graph of soil temperature and seed germination. source

Seeds need four things to germinate properly: heat, light (or lack thereof), moisture, and oxygen. Every seed is different and needs different amounts of each of these four variables. For now, let’s just talk about heat.

In a normal garden, your soil temperature is almost always 5-10 degrees cooler than your air temperature. This is due to water evaporation from the soil, causing evaporative cooling.

As spring comes around and the air temperature rises, the temperature of your soil follows suit — but it can take a while. Gardeners that want to take advantage of spring as soon as it’s sprung almost always opt to germinate indoors so they don’t have to wait for the soil to warm up outside.

There are other benefits to using a seedling heat mat as well. Your seeds will be provided a uniform temperature that can be calibrated to the exact requirements of the specific seeds you’re trying to germinate (if you have a seedling heat mat with a thermostat).

By providing your seeds with the optimal temperature, moisture, light, and oxygen, you are sending them a signal that it’s time to start growing.

Should You Get a Heat Mat With a Thermostat?

The Best Seedling Heat Mats and Thermostats

In short: yes.

While you might save about $10 buying a cheap seedling heat mat without a thermostat, the benefits of having one are too big to ignore. Temperature is so important in the germination phase, so having the thermostat will allow you to more finely control and set safety shut offs.

If you decide not to buy one with a thermostat, you’re not completely out of luck. Almost all quality plant heating mats come with a built in safety shut off that will trigger when the heat mat reaches a temperature of 10 degrees above the room temperature. However, this means you have to germinate in small rooms, otherwise the heat mat will work too hard to keep the temperature 10 degrees above a colder room and burn itself out.

The Verdict: Either buy a heat mat with a thermostat, or germinate in a smaller room. I personally like the flexibility and control of the thermostat. It’s not much more expensive, so it’s worth it to me.

Seedling Mat FAQ

Q. Do I leave the heat mat on 24/7?

Yes, you leave it on 24 hours a day…but only during seed germination. Once your seeds sprout and start to pop out of your Rapid Rooters or soil, you should remove the heat mat. Otherwise, the temperature will be too high and your roots will effectively get “cooked.”

Q. How do I know what soil temperature my seeds need to germinate well?

Because each plant is different, look at the back of your seed packet to figure out the right temperature and timing. Almost all of them will tell you what temperature to shoot for.

Q. What type of growing medium should I use for germination?

I personally use Rapid Rooter starter cubes. They don’t make a mess, hold moisture well, and are easy to transplant. But you can use standard potting soil or seedling mix as well if you want to.

Q. Can I make a DIY seedling heat mat?

Here’s a pretty good tutorial for DIY seedling heat mats, but I would personally not bother with it unless you get a lot of joy out of making things yourself. It’s probably less effective than a commercial heat mat, and when the most expensive heat mats are around $30 it just doesn’t seem worth it to me.

Best Seedling Heat Mat With Thermostat

Apollo Horticulture 9"x20" Seedling Heating Mat and Digital Thermostat Combo Set
  • Package Includes 1 - Apollo Horticulture Heating Mat and 1 -...
  • Dimensions: Dome - Heat Mat - 9"x 20" / Thermostat: 5.25" x...
  • Heat Mat Warms root area to 10 to 20°F above room...
  • Thermostat provides constant optimum temperature between...
  • Package Includes: 1 - Heat Mat / 1 - Digital Thermostat

The Apollo Horticulture 10”x20” w/ digital thermostat is the best heat mat with thermostat. Apollo is a fantastic manufacturer of many different horticultural products, many of which I use in my own garden. The thermostat can provide temps in the range of 68-108°F / 20-42°C, which is more than enough for any seed you’ll be growing. At $29.99 it’s also barely more expensive than a normal seed mat.

Best Standalone Seedling Heat Mat

Hydrofarm FBA_JEN-2047 Jump Start MT10006 Waterproof Durable,17 Watt UL Certified Seedling He, 9...
  • Warms root area 10-20˚F over ambient temperature to improve...
  • Hydrofarm is the only UL-listed seedling heat mats on the...
  • 6 foot Power Cord and Waterproof construction
  • 50% thicker construction
  • Lighting, watering, and planting information printed on mat

If you have a digital thermostat already or have a small, dedicated germation room and don’t need a thermostat, go with the Hydrofarm 9”x19.5” seedling heat mat at $20.50. This is the first heat mat I ever bought and I still have it to this day. I use it when I know the conditions that I’m growing in and don’t need a thermostat.

Best Large Seedling Heat Mat

Sale
Hydrofarm MT10009 Hydroponic Heating Pad,107 Watt UL Certified, 48 x 20.75 Inch Black
  • Warms root area 10-20˚F over ambient temperature to improve...
  • Hydrofarm is the only UL-listed seedling heat mats on the...
  • 6 foot Power Cord and Waterproof construction
  • 50% thicker construction
  • Lighting, watering, and planting information printed on mat

The large seedling heat mats are a recent pick-up for me. Now that I have started growing microgreens more and more, I find that having the larger surface area for my heat mats is a much more efficient way to germinate them.

Here, the best choice is the Hydrofarm 48”x20” heat mat with the Jump Start heat mat thermostat. You can fit four standard 10”x20” plant propagation trays on this bad boy, making it much more efficient for the money if you’re starting a large quantity of seeds.


The Green Thumbs Behind This Article:


Kevin Espiritu
Founder

Seeds germinate much better in warm soil, but how do you do that indoors? With a seedling heat mat. Find out how to use them and which are the best here.
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Last update on 2019-03-25 / Affiliate links / Images from Amazon Product Advertising API

2 thoughts on “The Best Seedling Heat Mats and Thermostats”

  1. I’ve been growing microgreens for 7 years but am just starting to use a heating mat for germination. Which seeds would you recommend apart from basils? I’m guessing shiso, chervil, cilantro, fenugreek, beets, amaranth, sunflowers, gem marigolds? Not kale, fava, peas, arugula, spigarello, Daikon? Thanks in advance for any advice you can give me!

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