First off, you need to pick a box robust enough to handle rough treatment. This increases the chance of your plant getting to its recipient in one piece. Also, when selecting the right size box, choose one that's just large enough for the plant to sit inside. You don't want room for it to slide around. If there's excess space inside the box, add some extra cushioning. You don't have to use anything fancy - old newspaper will do. Just scrunch it up and fill in any pockets of space. If it's a potted plant, protect it in bubble wrap. We suggest placing a collar of cardboard over the soil and the base of the plant. Then secure a plastic bag around the bottom to ensure the earth remains inside the container. Last but not least, reinforce the edges of the box with strapping tape to add an extra layer of protection.