Tree Pit Design with the Greenleaf Product Range
Greenleaf products have been specially developed to meet the requirements of a successful tree pit design:
Soil volume requirements for trees can be estimated using several methods. In a natural environment a root system can extend two to three times the radius of the tree canopy. Probably the simplest way of calculating a minimum required soil volume is to take the projected canopy area of the mature tree, multiplied by a depth of 0.6m. The shape of this area can be configured to suit the particular site. Other methods are based on mature trunk girth, and are possibly more accurate as they provide for different foliage shapes. The old method of providing a tree pit area the size of the pavement opening is clearly insufficient, and commits the tree to an untimely death, or a lifetime of costly repairs.
Engineering Requirements – With many trees pits located immediately adjacent to highways and engineered structures, it is vital that root volume is considered. Engineering requirements for hard surfaces are directly opposed to horticultural requirements so structural soil modules or similar must be considered early enough in a project to be incorporated into the tree pit design.
Root Management – Paved surrounds or utilities nearby? If so, root management should be specified depending on what needs protecting and where it is in relation to the tree pit. For a continuous paved surround for example, roots will need to be managed downwards by at least 300mm to design out paving heave. See our section on root management for further details.Irrigation – Lack of water and nutrients are the biggest single killer of newly planted trees in the UK. Tree pit designs should incorporate the means to irrigate efficiently, particularly for the first three years.
Drainage – Water logged tree pits can become anaerobic and this will kill the tree. Ensure that drainage has been thought through early on in your scheme.
Aeration – Less widely known but none the less important, soils and roots need air to live.
If the root plate of the tree is covered with impervious paving, vital gaseous exchange in the root zone cannot take place. Appropriate tree pit design should include a means of facilitating air supply below ground.
Support – How will you ensure the tree is securely located? Underground guying is widely favoured for urban tree pits as it is unobtrusive. Staking and tying is an alternative but this will require maintenance.
Above Ground – What sort of environment will you be planting in? In some locations above ground protection from carelessness and/or gratuitous vandalism becomes critical to tree survival. A decision will need to be made on whether there is a need for tree grilles, vertical guards and other protective measures around the tree pit.
The above factors cover over 90% of reasons for urban tree failure. Greenleaf’s Arborsystem products can be used in combination to address any or all of them as need dictates, giving you the confidence that your tree pit design will be efficient and successful, producing vigorous and healthy trees.
