Official Web site sponsor:

• Will you be hanging it? If so, go with a lightweight container. This may mean that it's relatively small. The heavier the pot, the sturdier the hook, chain, or other hanger you'll need.
• Will you need to move it once in a while? Even if your pot will remain earth-bound, consider whether its location is permanent or if you'll need to move it. Large containers of moist soil are very heavy. (Ask the custodian if you can borrow a dolly to move large ones!)
• What are you growing? Different plants require different amounts of soil. Small annuals like alyssum and lobelia have compact root systems; tomato plants and patio trees need more space.
• How often are you willing to water it? Small containers dry out more quickly than larger ones and may need watering twice daily in hot, sunny, or windy weather.

Drainage Considerations

• For plants to have healthy roots, soil needs to drain well. If a container lacks holes or other methods for drainage, excess water may drown roots. On the other hand, plants can suffer if a container dries out too quickly. Porous materials such as unglazed terra cotta and wood dry out faster than plastic and polyresins, so you'll need to water them more often. But they have the advantage of keeping plants from getting waterlogged. (Large containers of either type retain moisture better than smaller ones.) The materials you choose depend on your climate, the plants you're growing, and how often you can water.
• If a container doesn't already have drainage holes, make 1/2-inch holes at or near the bottom. If holes are at the bottom, elevate the pot on blocks, bricks, or "pot feet" so water can drain out. If you put holes in the side an inch or so from the bottom, the space below the holes will retain extra moisture. To keep from losing soil out of larger holes, line your containers with newspaper or nylon mesh window screening, which will also prevent pests from entering. If your container has no drainage holes and it isn't practical to make them, you can place a smaller, less decorative container with drainage holes inside the first one.
• If you have a container that won't hold onto soil or water well, such as a woven basket or old boot with holey soles, you can line it with thick plastic, bubble wrap (used for shipping), or a plastic milk jug or soda bottle, and punch drainage holes in the lining with a nail or pencil. Wire hanging baskets lined with sphagnum moss retain moisture, but also enable water to drain easily.

Other Thoughts

• Avoid using containers made of older pressure-treated wood, which may contain toxic chemicals that can harm plants and people. Recent regulations have banned the use of arsenic-based wood preservatives, so newly purchased pressure-treated stock should be fine for ornamental plants. If you’re growing food crops, use an alternate material. If you build your own wooden boxes, use rot resistant wood, such as cedar. Also, avoid containers that previously held toxic materials such as paint.
• Choose your container based on the type of plants you want to grow. It's important to match the plant with the proper container. You'll also need to consider the challenges of your climate, and how much time you can devote to caring for your plantings. Check out Plants for Containers for more guidance.