Drainage is essential so that the planting mix will not become water-logged. Do not place pebbles or other material at the bottom of the container. They will not provide better drainage. Plastic or wire baskets are available. Both have advantages and disadvantages.
Plastic is inexpensive, easy to plant and is slower to dry out.
Wire baskets allow more choices in size and planting arrangements. Many people find them more attractive. Window boxes are usually plastic, wood or long wire baskets called hayracks. Liners are used in wire hanging baskets to hold the soil and plants in position. Liners can be made of dried sphagnum moss or coconut fiber known as coir.