The 5 Best Seedling Heat Mats and Thermostats

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 has a warm temperature range.

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 plant heating mats you should consider and what you should be looking for!

The 5 Best Seedling Heat Mats

1. Epic Seed Starting Heat Mat

Our Epic Seed Starting Heat Mat is a great option that fits many different situations. While it lacks the ability to control a stable temperature range via a thermostat, it offers everything you need to warm up your starting trays and get those seeds going!

The heavy-duty PVC material on this heating pad is water-resistant, and lasts for years so you can keep using it season after season. This also ensures the mat and power cord are safe. Its dimensions fit under any universal tray you have — though we’re partial to our Universal Bottom Tray which fits any standard humidity dome. Compared to other seedling heat mats, it requires a lower wattage, helping you save on your electricity bill.

One of the coolest features of this product is the accompanying charts you can reference. Printed on the seedling mat is not only a peat-free seed starting recipe, but also a chart that shows different germination times. It also increases the temperature of the tray 10 to 20 degrees Fahrenheit above ambient temperature. Set yourself up for success and spring for this one as you prepare for the growing season!

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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 seedling mats provide steady temperature across their entire surface.

This 20″x20″ standard heating pad gives you enough space to get two seedling trays started side by side. If your space is limited but you’re trying to use it to its fullest, this heating pad is a great alternative to the standard 10″x20″. If you have standard trays, you can even use humidity domes for a boost to your seedlings as you keep the soil warm.

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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 that provide gentle warmth is a much more efficient way to germinate them.

Here, the best choice is the Hydrofarm 48”x20” seedling 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 than most heat mats for the money if you’re starting a large quantity of seeds.

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4. Vivosun Seedling Heat Mat & Thermostat Set

Looking for a kit that combines both a reliable thermostat and your heating pad? Vivosun’s 48″x20″ mat has been packaged as a digital thermostat combo set in this starter kit. This gives you enough warm surface area to handle four propagation trays while ensuring they stay exactly at your desired temperature.

Their digital thermostat combo keeps temperatures set between 68-108 degrees Fahrenheit (20-42 degrees Celsius) 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 as you grow healthy plants.

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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 mat. In addition, you’ll probably want a grow light of some sort. A thermostat helps you dial in the right temperature easily.

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, stable heating system with a thermostat. It even has a stronger heating wire. Use a 72-cell starter tray in your germination tray and you’ll have a great start to your garden in no time.

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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’s temperature is almost always 5-10 degrees cooler than your ambient 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). You’ll also grow healthier plants as the stronger heating wire offers heat, or small electrical coils inside provide warmth.

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. So you may want to opt for heating pads that include more uniform heating temperature controls.

Should You Get a Seedling Heat Mat With a Thermostat?

In short: yes.

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

If you decide not to buy heat mats with a thermostat, you’re not completely out of luck. Almost all quality seedling heating mats come with a built-in safety shut off that will trigger when the heat mat reaches a temperature of 10 degrees Fahrenheit above the ambient 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 Fahrenheit above a colder room and burn itself out. Unless you’re working with a digital thermostat with more exact temperature controls, that is. A lack of thermostat controller could mean uneven heating patterns in this regard.

The Verdict: Either buy a heat mat with a digital thermostat controller to maintain warm temperatures or germinate in a smaller room. I personally like the flexibility and temperature 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 seed 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 or more heat mats.

If you’re a microgreens fan, you’ll probably want pretty large heat pads 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 and the right number of heat mats for your germination process needs!

Frequently Asked Questions

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

A: Yes, you leave it on 24 hours a day…but only during 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?

A: Because each plant is different, look at the back of your seed packet to figure out the optimum soil temperature and timing. Almost all of them will tell you what temperature to shoot for. If you have a thermostat, you can produce heat at a target temperature for that plant. Most heat mats raise the temperature enough degrees Fahrenheit to warm the soil well.

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

A: I personally use Espoma Seed Starting mix. But you can use standard potting soil or seed starting mix as a growing medium if you want to.

Q: Can I make a DIY seedling heat mat?

A: 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 seedling heat mats are about the same cost as your parts, it just doesn’t seem worth it to me.

Q: What should I look for in a seedling heat mat?

A: The basis should be what you need to help those seeds grow. As long as it raises the soil temperature to around 75 to 85 degrees Fahrenheit (24° to 29°C).

Q: Can you leave seedling mat on overnight?

A: Yes. In fact, most heat mats have an automatic shut off feature that will turn it off if it gets too hot. So you shouldn’t have to worry about any problems keeping your heating pads on overnight.

Q: What do you put under a seed heating mat?

A: You want to keep heat mats flat, but you can also put a towel between them and the surface you’re growing on. Most are water resistant, and won’t need this, but if you do, remove the damp cloth and replace it with a dry towel often.

Q: How big should seedlings be before hardening off?

A: When your seedlings are a few inches tall, they’re ready to be hardened off. You can take them off the heating pad when they’re fully sprouted, unless you can turn the heating element down.