Since the seedling season is starting, I was asked several times if it’s necessary to have a heat mat to make your seeds germinate. Honestly, I was a little confused. Although I was bathed in horticulture all my childhood and eventually came to work in the field, I have never owned a seedling heat mat. I know, it’s a little embarrassing…
Yet, I have started a ton of seedlings in my lifetime! When I was young, we did it indoors, under fluorescent lights, for our vegetable garden. I also lived for a few years on a farm where we produced vegetables that were sold to a very select clientele (in other words: friends and family). And for the past few years, now that I have a small outdoor space with just enough light for a few vegetables, I’ve been starting seedlings in the spring.
So, is it necessary or not?
As you can see, it isn’t, since I’ve been doing just fine without a mat for years! But it can still be useful in some cases.
What’s a Seedling Heating Mat?
Their construction can be quite simple: heating elements surrounded by insulation and a layer of vinyl. Some models include temperature controls when you want to be really precise, otherwise they just turn on and off.
They raise the temperature on their surface by about 8°C to help the seeds germinate. It is generally said that seeds germinate best at a temperature of 19-24°C. In truth, each type of seed has an ideal germination temperature, as you will see in the list at the end of this article.
You should also take into consideration that most of the time, the temperature of the soil is cooler than the ambient air. You can check its temperature with a cooking thermometer. Or not!
Most heating mats are about 10″ x 20″ to accommodate a seedling tray. However, they come in many sizes. I’ve seen some that were 3 inches wide, designed to fit a windowsill, and others that were 2 feet by 4 feet, on which you can place 4 seedling trays.
Use
Using them is child’s play: connect the heating mat to a power supply, turn it on, place a seedling tray or other container with your pots on top. That’s it! With an ideal temperature, the seeds can germinate faster and, in some cases, you can save a few days.
Warning: If your pots or containers are made of polystyrene or other insulating material, a mat will not help because the heat will not reach your seeds.
Remember that once your seeds have germinated, the heating mat is no longer useful, as it warms the soil and not the air.
So, Is It Useful or Not?
A heat mat can sometimes be useful, but it isn’t necessary. It really depends on the environment in which you are growing your seedlings.
Personally, I start my vegetable seedlings under my desk with a full spectrum LED grow light. When the planting season starts, I turn up the temperature in my office a bit, so it’s almost ideal for germination.
No problem! To keep the humidity up, I germinate my seeds under a dome, in a plastic bag or under a glass window. Because of the greenhouse effect, the temperature is higher in these mini greenhouses, so there is no need for a heating mat.
Also, if you use artificial lighting, be it fluorescent, LED or other, the temperature will increase even more. So I don’t use a heat mat, I don’t even check the temperature of my soil. I sow without even thinking about it. Either you’re laidback or you’re not! That said, some of you are probably sowing in conditions that require a little more dedication.
Needed for Some
Let’s say you grow your seedlings in natural light, near a window. You may not cover them, because in full sun, with the famous greenhouse effect, they may get too hot and burn. Also, with the cold temperatures at night, the proximity of the window could be a disadvantage. So, a heating mat would be very useful for you.
Another case where a heat mat becomes essential is in a greenhouse. It’s unlikely that you will heat your greenhouse to the temperature needed to germinate your seeds. If so, a heat mat becomes an indispensable tool!
Beware of salesmen who want to inflate your bill by trying to give you a “seedling starter kit” with a heating mat even if you don’t need the mat!
I’ll wait until I need before I buy one. Unless you think that by having a seedling heating mat, I can justify the purchase of a greenhouse to my girlfriend… Can’t blame a guy for trying!
When I do my seeding, the pots are placed under an LED light in a space about 50in by 30in by 24in high in my basement. It is a closed space where the temperature is normally about 14-15C. I also turn on a small lamp with an incandescent 100w bulb that runs 24h a day which raies the temperature to 19-20C. No other equipment is necessary.
Exactly. We use heat on the farm only to accelerate and enhance production. However, for my own home garden, such acceleration and enhancement is unnecessary. I do not expect all vegetable seed to germinate, and I am in no rush for them to do so. The only exception was when I grew Sabal minor from seed, and it will not germinate without getting warm.
I have used soil heating mats for years. My basement is very cool 16-18C all winter and while the mature plants like it the seeds germinate better on them and cuttings root far faster. Incidentally I bought my tray sized one for my elderly cat some 20 years ago. It was used all year round for 5 years and used seasonally ever since.
I agree a heating mat is really needed for most seedlings. However, they do come in handy when germinating plants that like warmer conditions to germinate in such as tropicals and peppers. They are also handy for rooting cuttings. They root far more quickly with some bottom heat.