A planting bed should always be made large enough to accommodate plants when they reach mature size. The length and width of a flower bed depends on how many flowers are to be grown. Ideally, between 100 and 500 square feet provides room for root systems. A bed also should be big enough so you can get inside to do routine maintenance (watering, pruning, fertilizing and raking).
A bed that is exclusively a flower border containing only perennials and bulbs can be narrow — perhaps only two to three feet wide, and as long as you want. This allows you to maintain the bed from the lawn or hardscape bordering the bed. If a bed becomes much wider, adding spaces of open mulch or stepping stones will make maintenance easier over the long run. Repeated footsteps in a large flower bed will compact the soil.
Raised beds should be accessible from one side and should be no wider than 2 feet. If the raised bed is accessible from two sides, the bed can be 4 feet wide.
A planting bed that consists of trees, shrubs, perennials and ground covers can be much wider, but you still need to provide open spaces for maintenance. In this type of bed, plants typically are arranged with taller plants in the rear and lower growing plants in front.
If a deciduous tree is placed in a planting bed, the bed needs to extend only about two to four feet beyond the trunk. That protects the tree from lawn mowers and creates an interesting transition area between the tree and the lawn. Planting beds for evergreen trees such as spruce and some pines need to be large enough to encompass the mature diameter of lower branches.
For more information, see the following Colorado State University Extension fact sheet(s).
- Ornamental Grasses
- Xeriscaping: Ground Cover Plants
- Ground Cover Plants
- Perennial Gardening
- Evergreen Trees
- Small Deciduous Trees
- Large Deciduous Trees