A seed box, or flat, provides space to grow multiple seedlings in a single container. These shallow boxes are typically between 3 and 4 inches deep, which provides enough root space for young plants. A single container takes up less space than multiple pots and is easier to move to a new location when necessary. Transplant the seedlings to an individual pot or out in the garden once the plants outgrow the seed box.
Things You'll Need
Soak used seed boxes in a solution of one part bleach to nine parts water for half an hour. Rinse with clear water before using. Bleach disinfects the box so no plant disease pathogens transfer to the new soil or plants.
Line the inside of the box with a single sheet of newspaper. Newspaper allows excess moisture to drain from the slits in the bottom of the box, while preventing the soil from falling out.
Set the box on top of a shallow tray that is slightly larger than the seed box. The tray catches the excess water as it drains from the box.
Fill the box to within a half inch of the rim with potting mix. Use a soilless potting mix for germinating seeds and growing seedlings, as these mixes are sterile and drain well in the small seed box.
Water the potting mix thoroughly 30 minutes before seeding. Soak the soil and allow the excess to drain out. Empty the drained water from the tray beneath the seed box. Plant the seeds as directed on the seed packet.
Poke small holes in the bottom of a plastic tray, if you prefer to make your own seed box. Any shallow box works well as long as drainage is provided.