Don't discard plastic strawberry containers if you're planning to grow your own seedlings. Those little mesh-like baskets work well as no-cost seed starters and seedling nurseries. Growing seedlings in repurposed plastic strawberry containers makes sense from another viewpoint: recycling plastic items to keep from adding more trash to landfills. They can be cleaned and reused many times.
Line the bottom and insides of the plastic strawberry container with two or three layers of old newspapers.
Fill the container to within one-half inch of the top with a seed-starting mix. Water so the mix is evenly moist but not wet or soggy.
Press seeds about one-half inch apart into the top of the moist starting mix. Cover them with the appropriate depth of medium, depending upon their species. Water enough to evenly moisten the surface.
Place the container on a flat surface where it will receive the correct amount of light and warmth for the species planted. Care for these seeds as you would if they were planted in any other container. Check them daily to make sure they don't dry out.
Thin the seedlings to one to four plants when they're about 1 inch tall. The type of plant will determine how many can remain in the plastic strawberry container.
Move the container outside when the weather has warmed and no further frost is expected for the season. Dig a hole large enough to accommodate the whole package and position it so the seedlings will be planted at the same depth they currently occupy. They'll be spared the shock of transplant, and their roots will grow right through the newspaper.
Flip an empty plastic mesh container upside down to cover the seedlings. This will protect them from birds that enjoy eating tender young plants. Remove the containers when seedlings are tall enough to begin reaching through the tops. When they're this mature, they've grown tougher and the birds won't like them anymore.