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.
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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.
Let’s go over which mats you should consider and what you should be looking for!
The 5 Best Seedling Heat Mats
1. Growerology 10″x20″ Seedling Heating Mat
There’s a lot of 10″x20″ mats on the market, but I’m particularly fond of this one by Growerology. It’s not that the heating mat itself is special, although it’s certainly reliable and worth getting on its own. What draws me to it is that they’ve included a reflective mat to place underneath your seedling mat. The reflective mat redirects heat that would be lost down into your growing surface back towards your plants where you want it to be.
- ✅ BETTER, FASTER RESULTS: Are you tired of…✅ GROW BIGGER, HEALTHIER PLANTS: Heating…✅ DURABILITY: 10" x 20.75" MET certified…
2. Vivosun 20″x20″ Seedling Heat Mat
In recent years, Vivosun has emerged as a quality supplier of heat mats. Fully waterproof and resilient, these mats provide uniform temperature across their entire surface.
- Reliable Results: The VIVOSUN professional heat…Stable & Uniform Heat: The advanced far-infrared…Built to Last: Designed with soft, flexible, and…
This 20″x20″ mat gives you enough space to get two trays of seedlings started side by side. If your space is limited but you’re trying to use it to its fullest, this is a great alternative to the standard 10″x20″.
3. Hydrofarm 20″x48″ Heating 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.
- Warms root area 10-20˚F over ambient temperature…6 foot power cord and waterproof construction with…Daisy chain up to 5 units (4 add-on units MTMDA…
Here, the best choice is the Hydrofarm 48”x20” heat mat with a 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.
4. Vivosun Heat Mat & Thermostat Set
Looking for a kit that combines both a reliable thermostat and your heating mat? Vivosun’s 48″x20″ mat has been packaged with their own digital thermostat in this starter kit. This gives you enough warm surface area to handle four propagation trays while ensuring they stay exactly at the temperature you want them to.
Their digital thermostat keeps temperatures set between 68-108°F at the temperature you’re aiming for. Simply poke the probe into the soil of one of your trays, set it at the ideal range, and let the mat work its magic.
5. iPower Seed Germination Starter Kit
We all started somewhere, and if you’re just getting started with germinating your own seedling plants, you’ll need more than just the heating mat. In addition, you’ll probably want a grow light of some sort. A thermostat helps you dial in the right temperature easily.
- Multifunction: great for indoor plants, for better…Professional reliability: heat mat maintains…Energy efficient: T5 high output fluorescent…
Thankfully, iPower has the beginner in mind with this starter kit. It includes a sturdy metal light stand, a 4 foot T5 grow light, a 10″x20″ mat to handle one very healthy tray of seedlings, and an easy-to-set thermostat. Use a 72-cell starter tray in your germination tray and you’ll have a great start to your garden in no time.
Why Should You Germinate with a Plant Heat Mat?
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?
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 shutoffs.
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.
What Size Seedling Heat Mat Should I Get?
This is a tricky question because it depends on how you’re starting your seedlings. But, in short, it depends on how many trays of plants you’re starting.
The average germination tray is 10″ x 20″ in size. If you’ve got a small cell germination tray that can hold 72 seedlings, that may be all you need for a small garden.
But if you’re using peat pots for ease of later transplant, you might find you’ll need more than one tray to hold their larger size. And if you do need more than one tray, you’ll want a larger mat.
If you’re a microgreens fan, you’ll probably want a pretty large one just so you can rotate in and out trays as needed. A 48″ x 20″ mat will easily hold four germination trays side by side, where a 20″ x 20″ mat can only support two trays.
Plan ahead to be sure you get the right size of mat for your germination needs!
Frequently Asked Questions
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 Espoma Seed Starting mix. 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?
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 about the same cost as your parts, it just doesn’t seem worth it to me.
