Cut the tops off of any plastic containers that have a handle or narrowing spout. For example, milk jugs need to be cut just below the handle, while 2-liter soda bottles don't have to be cut until the top portion of the container begins to slope inward.
Fill a bucket with 1 gallon of hot water and 1 cup of bleach. Set your used plastic container in the bleach solution for up to 15 minutes to disinfect it. Any bacteria or organisms left in the plastic container can potentially harm the plants you pot in it.
Rinse the plastic container out with hot water. Scrub it with a soft-bristle brush and some hot water that has a few drops of dish soap in it.
Hold your plastic container under a faucet of hot running water until all traces of bleach and soap disappear. The container is now clean and ready for planting.
Fill the plastic container two-thirds of the way with potting soil. Dig a hole with your hands that is big enough to fit a plant root ball.
Place your plant inside the hole you prepared by dropping the plant's root ball in first. Water immediately, and then set it out in the sun.