I have one. Never needed it growing weed. Nor have I ever used a heating Matt. I start my seeds in Jiffy Pots and seed starter and keep them under CfLs until they pop thru and get about 3 or 4" tall. Then Jiffy Pot is buried into FF Ocean Forest in what ever sized pot I'm going to grow in. I use a razor blade to make several cuts in the sides and bottom of the Jiffy Pots which dissolve anyway.The roots grow until they break thru the Jiffy Pots. By then they can handle the FF Soil.
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