What sized tree to plant – the concept of “The Practical Minimum”

To achieve tree planting objectives there is a minimum sensible size a tree should be – “The Practical Minimum”. This is determined by listing the factors that will influence trees planted, as well as the influence trees will have on the planting site, and then allocating an appropriate sized tree to cope with those factors. The largest size on the list becomes the smallest practical tree size – “The Practical Minimum”. Trees planted smaller than this will cause problems related to at least one of the major influences.

For example, in a residential streetscape major factors to be considered might include:

• a preference for major visual impact at planting;
• a desire to reduce the likelihood of destruction by vandalism; and
• the critical need for clear sightlines for vehicles using the street or emerging from driveways.

200-300 litre plants might satisfy the first two of these criteria, but the need to protect sightlines dictates that the stem (or trunk) of the tree needs to be “clean” up to at least 1.5-1.8 metres. That, in turn, dictates the tree should be at least 4-4.5 metres tall, which means a 400 litre tree or larger. So 400 litres the minimum size that will satisfy all criteria be – “The Practical Minimum”.