Many types of seeds can be direct sown, straight into the garden soil. While some seeds benefit from being planted in frosty conditions when the soil is still cold, many benefit from sowing when the soil begins to warm up in spring. But some seeds need to be started indoors to be given a chance to grow past the seedling stage before being transplanted out in late spring or early summer. Plants like tomatoes, peppers, eggplants, and melons perform better if they are started indoors this way. The same can be said about woody herbs and many perennial flowers.
Of all the tools to help start seeds indoors, perhaps the most useful is the Seedling Heat Mat. This is a waterproof plastic mat that is sized to perfectly fit beneath one (or more) standard 10 x 20" seedling tray. Once it is plugged in, the mat generates a very moderate amount of heat which raises the temperature of the soil by about 6-11°C (10-20°F) warmer than the ambient temperature. The heat is subtle, but constant.
Warm, moist soil simulates a beautiful spring day, and seeds burst into action with surprising uniformity and speed.
By their nature, strawberry seeds have a fairly uneven rate of germination. If twenty seeds were planted, two might come up in the first week, some a couple of weeks later, and the rest after a month - or longer. On a Seedling Heat Mat, the germination is far more even, with most of the seeds woken from dormancy after about ten days.
The Heat Mats are fairly thick, with several layers of plastic heat bonded (not glued) over a strong heating wire. Water can't get into the mat so there are no electrical worries when irrigating plant trays. At the end of the seed starting season we just roll them up and store them for next year — and we've been using the same ones for more than five years.
The mats can also be used to propagate from cuttings, since the warm soil stimulates root growth. Be sure to remove seedlings from the mats after germination to slow down the growth and keep the seedlings stout and healthy.
Another feature is that they are sized for versatility, to suit the needs of the home gardener to greenhouse grower.
One standard 10 x 20 planting tray fits neatly over the 10 x 20 Seedling Heat Mat, which is perfect for germinating tomato seeds, pepper seeds, and some early perennial flowers and herbs.
For bigger planting jobs, the 20 x 20 Seedling Heat Mat fits two trays, side by side. This can simply double the number of seedling cells, or more than one size of seedling cell can be used together... As in one Plug Insert 24 Cell for germinating cucumber seeds beside one Plug Insert 72 Cell for germinating lettuce or other small crop.
Greenhouse growers and serious gardeners will appreciate the 20 x 48 Seedling Heat Mat, which neatly accommodates four planting trays side by side for larger scale production. As we prepare for planting our seed trials and seedlings for our Annual Tomato Seedling Sale, we unroll several of these in our greenhouse and use Plug Inserts Professional 72 Cell trays. This is the only way we can produce thousands of tomato seedlings at once.
For those of us who plan on starting seeds indoors each spring, a Seedling Heat Mat is a very sensible investment. They're only plugged in over a few months in late winter and early spring, but they make seed starting efficient and fast.