Be on the lookout for possible containers in your yard, closets, in the garbage, at garage sales, thrift shops and dollar stores. Almost anything that can hold dirt and be drilled with holes can be converted into a container flowerpot. Yogurt cups, frozen juice cans, tuna cans and old margarine containers are perfect for starting seeds. Buckets, wooden crates or plastic storage containers are suitable for just about any plants. For something more unusual, consider discards such as old sinks, cooking pots, baskets, dresser drawers, milk cans, toy wagons, laundry baskets or worn-out boots. Larger containers can be made out of bathtubs, children's wading pools or an old rowboat.
Wash your container thoroughly with a mild dish detergent and rinse it out well. Sanitize the container with a solution of 1-part chlorine bleach to 9-parts water. Fill the container with the solution and let it sit for 20 minutes, then rinse it.
Select a container based on the space your flowers need to grow. Some flowers, such as sunflowers, will benefit from larger containers so they will have more space and can root more deeply. Others, such as impatiens and African violets, have shallow roots and require little space between plants. These are better for shorter or narrower containers.
Make holes on the bottom of your container for drainage, if it doesn't already have drainage holes. Some materials, such as woven baskets, do not require this. Use a drill or utility knife to make holes, depending on the materials your container is made of, to space holes 4 to 6 inches apart on the bottom. The less porous the material, the more holes you will need.
Line your container with plastic sheeting if you feel it is necessary. Sheeting will prevent soil and gravel from spilling out of containers with larger openings, help retain water in containers that are too porous, or protect plants from treated materials that might leach into the soil. Cut some holes into the bottom of the plastic to promote drainage.
Place a shallow layer of some material at the bottom of your container to help promote drainage and aeration, as well as prevent soil from seeping out. This can be pottery shards, rocks, gravel, Styrofoam packing peanuts, marbles or crumpled newspapers.
Add slightly damp potting soil or compost to your container. Sow seeds directly into the container, or transplant seedlings. Water the plant deeply and allow the growing medium to settle. To help retain moisture, add a layer of mulch.
Stand your container on something to prevent it from laying flat on the ground or soil so that the drainage holes are not blocked. Use things such as flat stones, bricks, wood blocks or terra cotta flowerpot holders.