In selecting plants for your beds and borders, the height and spread of the mature plant is one of those often ignored factors. This will affect how they fit into your design and how the plants, especially trees, interact with surrounding buildings and hardscape.

A. Mature Size - The mature size of trees and shrubs is of great importance in landscape beds and borders. That nice little transplant that you bring home from the nursery may eventually grow into a giant redwood. Knowing the ultimate size and spread of the plant will help prevent situations where the trees grow into distorted shapes because they are planted too close to the house, fence, or other trees.

Perhaps the most important reason for long term problems with pines and spruces discussed earlier is that they are planted too close to each other. Eventually, their foliage and root systems grow together and they become very susceptible to needle diseases and other problems.

Knowing the projected mature size of perennials is also important. This will help you determine the realistic spacing between plants to allow them to form properly and not become crowded.

B. Scale and Proportion - Knowing the ultimate height and spread of your plants will also help you to maintain a proper sense of scale and proportion in your landscape. Sure, you have the power of the chainsaw at your disposal but trying to keep a tree or shrub from growing to its natural size is usually a losing proposition. You can keep cutting it down to size but the trunk and side branches will eventually get out of their natural size relationship. This will result in an unnatural, "awkward" looking plant.

C. Beds and Borders - Of course, the key reason for arranging our plants in beds and borders is to be able to see them easily and in the right position relative to the other plants. So, paying attention to the mature height of plants is important to fulfilling our design intent.

1. Plant Heights for Beds - Beds are free-standing arrangements where we can walk all the way around and view the plants from several different perspectives. To be sure that plants are not blocked by others, we need to place the tallest plants in the center of the bed and have the heights drop gradually to the outside of the bed.

   The general rule is that the tallest plant should be about half of the width of the bed in order to appear in proportion. That would mean that, if the bed is 8 feet wide, the tallest plant should be no taller than around 4 feet in height.

   Also, the term "gradual" decline in height is often considered to be about a 4 to 8 inch step down with each layer of plants. That would mean that, if the center plant is 42 to 48 inches in height, then the plant on the outside of it should be around 34 to 38 inches tall so that there isn't an overly large gap between the two.
    

2. Plant Heights for Borders - By definition, borders have a definite backdrop to them. The plants are viewed in front of a building, fence, hedge, wall or other structure. So, naturally, you would want to put the tallest plants next to the backdrop with a gradual decline in plant height toward the front of the border.

As with the case in beds, you want a gradual drop in height between each row of plants. This will give a smooth transition from one group of plants to the one in front of it.

Avoid the "crowded" look by allowing enough room for each plant to attain its natural size and spread. Also, it is a good idea to allow a small path or alley between the back row of plants and the backdrop element. This will allow for air to move through and help minimize fungal problems. It will also act as an access point for maintaining the border without having to step into the planting areas too much which will compact the soil.