A Seedling Heat Mat - gets 'em going!If you're going to start vegetable gardening from seed, use a seedling heat mat to get your seedlings off to a good start. Seed heat mats are used to warm the soil in seed trays to temperatures that are most conducive to germination. They are essential if you're trying to get a jump on the season. Without a seed heat mat, you'll have limited germination, erratic germination, or no germination, especially if you're trying to get ahead of the game in cool soil. You'll also have to wait until the soil heats up before you can plant. This could delay planting by as much as 8 weeks. For many vegetables, you'll need this head start in order to have a successful yield. Tomatoes and eggplant are two examples. If you don't start them before the growing season in northern areas, then don't expect to have any fruit at all by the end of the season. Seed Heat Mats - three typesThere are three types of seed heat mats that I am aware of. The first type of seedling heat mat is a constant heat output device that you can't regulate. It simply is a resistant heater mat with a cord that plugs into the wall. Regardless of the temperature of the mat or seedlings, it keeps cranking out heat to whatever is sitting on top of it. 
The  heat mat shown to the right is just such a product. Again, they have a constant output, but the warmth they provide is moderate. There is no switch. It's on when you plug it in and off when you unplug it. There is little risk in keeping it plugged in as long as there is a seedling tray on it.These type of mats work fine, but don't expect them to overcome a cold surface or a generally cold environment. Also, you might want to invest in a temperature probe to make certain that you know the temperature of the soil that the seeds are sitting in. Generally 75 to 85 degrees F is about right for most seeds. Others can germinate at lower temperatures, but I don't know of any that complain about higher temperatures for germination. The second type of seedling heat mat makes use of an external thermostat that is connected to a temperature probe that turns the heat mat on and off based on the temperature that the probe "sees." It's a variation on the constant energy output design, except that the on/off switch isn't the wall plug, it's the thermostat. Hydrofarm makes numerous products like this, including a constant heat output model, and thermostats with probes that you can add to your seed heat mat as a control. They also make large seed heat mats that can accommodate 4 seedling trays. Here is a link to offerings such as the Hydrofarm seedling heat mat and other their other products. This will give you a good idea of what they offer in the line of seed heat mats.
Another option along these lines is really something of my own invention. It's a water bed heater mat. These are similar to the third type described above. They are temperature adjustable and thermostatically controlled. You select the temperature and the probe keeps it there automatically. So, if you're eager to get seeds started, then you'll want to invest in a seedling heat mat to make things go easier, faster and more reliably. They don't draw much current and they keep the environment favorable for the seedlings. Seed Heat Mats - non-standard applicationsSeed heat mats are highly water resistant if not waterproof, so they can be used in wider applications as suggested below:
A word of caution if you use a seedling heat mat in this manner: be certain to protect the thermostat controls from moisture that might accumulate inside a cold frame or under a clear covering. Also, be sure to install a drip loop so any water running down the cords doesn't find its way to the controls. Good fortune to you in your adventures with a seedling heat mat. They are a wonderful tool for any vegetable gardening enthusiast that needs to get seeds started early in the season. Done with Seedling Heat Mat, take me Home |
built-in thermostat
for control of heat output, as shown left. The thermostat turns the unit on and off based on a selected temperature. This offers more control with respect to heat input, and is necessary for seeds with a narrow optimal temperature range.