For many seed varieties, warm temperatures are critical to successful germination. Sometimes greenhouse temperatures aren't warm enough for certain plants to sprout successfully. That's why many gardeners use seedling heat mats to provide a heat source for immature young seedlings during germination. Seedling heat mats are easy to use and can provide immediate results, especially in quick-sprouting plants such as tomatoes. Here are some tips for using a seedling heat mat to encourage germination and plant growth.
About Seedling Heat Mats
Soil temperature is usually at least 10 degrees cooler than air temperature, so if temperatures are at 65 degrees Fahrenheit, the soil temperature will be 55. This is too cold for many seeds to germinate, because the optimum soil temperature for most seedlings during germination is around 75-80 degrees. A good seedling heat mat can increase soil temperature by 10-20 degrees and provide an even level of heat throughout the germination process.
Seedling heat mats are made of heavy, waterproof rubber and are fitted with internal heating coils that produce a gentle level of heat. Seedling heat mats typically measure around 9" x 19½" to fit under a single nursery flat, or 48" x 20" to accommodate four standard-sized nursery flats.
Most seedling heat mats have a built-in thermometer to help monitor soil temperatures, but these can sometimes get thrown off by the overall temperature of the room. That's why it's important to purchase a separate thermostat box with a temperature controller, which will provide precise monitoring of soil temperatures so that they can be adjusted whenever necessary. This type of monitoring is crucial, because if temperatures rise in the area, the soil temperatures will rise accordingly. For example, on a warm day, temperatures might rise as much as 15 degrees to a level that could damage seedlings. A thermostat controller, however, will adjust the heat in the mat so that the soil stays at a safe temperature level.
Using Seedling Heat Mats
To operate a seedling heat mat, choose a dry, low-traffic area and place an insulation mat on the floor for extra protection. Place the seedling heat mat on top of the insulation mat, making sure that it's close to a power outlet. Place the filled nursery trays on top of the seedling heat mat and place the thermostat box next to the mat, then insert the thermostat sensor directly into the soil. Plug the seedling heat mat into a power strip with a surge protector, then plug the thermostat box into both the power strip and the seedling heating mat.
The seedling heat mat should be kept on continuously throughout the germinating process; otherwise, extreme temperature changes could damage the seeds.
Seedling heat mats are especially beneficial for heat-loving plants like geraniums, petunias, tomatoes, peppers and basil, but they can also be used effectively for a wide variety of seeds. The average germination times will vary. For example, tomatoes are notoriously fast growers, and tomato sprouts may appear after being left on a seedling heat mat for only a night or two. Peppers and basil, on the other hand, may need to stay on the mat for as long as two weeks.
As soon as the seeds sprout and break through the soil's surface, they need to be removed immediately from the heat mat; otherwise, the plant roots might scorch. After removal, the plants need to be transplanted to their growing area as soon as possible.
How to Buy a Seedling Heat Mat on eBay
eBay offers a wide range of seedling heat mats from dealers across the country. To find seedling heat mats, just use the search bar to access available listings. Each listing will come with a full description of the mat, but be sure to email the dealer with any additional questions. eBay also has a full line of thermostat boxes, nursery flats, garden tools and seeds, making it a one-stop-shop for just about any type of gardening equipment.
Seedling heat mats are inexpensive, but they're extremely effective in speeding up the germination process and encouraging growth, especially when outdoor conditions aren't the best. Since many seed types only need to stay on the mat for a day or two, a couple of heat mats can be used for numerous nursery flats, which makes them even more economical for home gardeners.