You can start seeds in almost any type of container, as long as it’s at least 2-3 ” deep and has some drainage holes. If you love to DIY by yourself, you might start growing seedlings in yogurt cups, milk cartons, or even paper cups.
The “potting soil”
Choose the potting soil that’s made for growing seedlings.
NOTE: Do not use soil from your garden or re-use potting soil from your houseplants. Start with a fresh, sterile mix that will ensure healthy, disease-free seedlings.
Some of the small ones can be sprinkled right on the soil surface. Larger seeds will need to be buried. After planting seeds, you have to moisten the newly planted seeds. To speed up germination, cover the pots with wet paper or a plastic dome. This helps keep the seeds moist before they germinate. When you see the first signs of green, you have to remove the cover.
Watering, feeding, repeating
As the seedlings grow up, you have to keep the soil moist but not soggy. Let the soil dry slightly between waterings. Remember to feed the seedlings regularly with liquid fertilizer.
Seeds need a lot of light. Set the lights on a timer for 15 hours a day. If you’re growing in a window, choose a south-facing exposure. Rotate the pots regularly to keep plants from leaning into the light. If you’re growing under lights, adjust them so they’re just a few inches above the tops of the seedlings. Keep in mind that seedlings need darkness, too, so they can rest. As the seedlings grow taller, raise the lights.
It’s not a good idea to move your seedlings directly from the protected environment of your home into the garden. You’ve been coddling these seedlings for weeks, so they need a gradual transition to the great outdoors. About a week before you plan to set the seedlings into the garden, place them in a protected spot outdoors (partly shaded, out of the wind) for a few hours, bringing them in at night. Gradually, over the course of a week or 10 days, expose them to more and more sunshine and wind. A cold frame is a great place to harden off plants.