Sowing tomatoes in a cold greenhouse
Late March is the best time (in southern regions) to sow tomatoes outdoors. You can sow them under plastic, under five-liter bottles, or use a greenhouse box. In such small structures, it's easy to provide additional cover for the seedlings in case of a sudden cold snap.
But if you place a thick organic "heating pad" underneath the seedlings, the seedlings will be even warmer and more comfortable! ☺