Every gardeners needs to learn how to start seeds. This skill can save you hundreds of dollars.
Start with your recycled plastic trays and four packs. Wash them out with hot water and soap.
Use a seed starting soil mix, filling the cells in the four packs almost to the top. Sow seeds as directed on the packets. Generally, you'll want to sow two or three seeds in each cell, cover with just a bit more soil, and press them in with your fingers.
Water from the bottom to avoid washing the seeds around. About three quarters of an inch of water in the bottom of the tray is about right; the soil will absorb the water. Cover the seed tray with a clear plastic dome to create a humid mini greenhouse.
A heating mat under the tray will keep the soil evenly warm and aid in germination. Place the trays in a sunny window or under lights. Remove the heating mat and plastic dome after the seeds have germinated.
The seed packet will tell you when to start each variety. If it says "Start inside 6 to 8 weeks before the average frost free date," count back from May 10 (the average last frost along the Front Range). If you've never tried your hand at sowing seeds, try a practice batch of lettuce. It's easy, quick and delicious.