I came up with this idea after having a lot of trouble getting my okra seeds to ALL sprout. We had a week of 92 degree weather then it is 70 during the day and 50 at night for a week. Seeds do not like the 50 degrees nights the ground is cold so they don't sprout. I don't like rows with bare spots.
I cut 3 liter soft drink bottles in half they make nice little green houses to warm up the soil during the day so seeds will sprout. Bottles cut in half easy with a soldering gun.