Landscape Architecture through Planting

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Arboriculture: How a Landscaper should size up a tree

Field day sizing up a Robinia Pseudacacia

As a Landscape Architect, you may well be called in any given project to assess existing trees on a site.

You need to work within your capacity as a Landscape Architect and be aware that an assessment does not meet the complete analysis an Arboricultural Consultant would be able to provide.

Generally you'll be making an assessment from the ground (i.e. without drone access, possibly only with binoculars for augmentation.

You will however be able to assess the following by just looking

Foliage density - i.e. compared to an archetypal specimin is the foliage lacking?

Habit and aspect, the form of the crown and any directional growth (for example, an Aesculus hippocastanum (Horse Chestnut) examined in Greenwich Park showed signs of leaning, potentially from storm damage)

Virus, Pest or Fungal infections: the chestnut showed both leaf miner (Cameraria ohridella) and leaf mould (most likely guignardia)

With a couple of simple tools you can make further observations

A nylon mallet can be used to assess if the tree is hollow

A wire probe can be used to examine any holes or cavities

In all cases, findings should be logged, so that any future. assessment (such as the hole getting bigger) can be cross-referenced.

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Urban tree planning

How are trees grown for the planting environment?

Nurseries will closely grow plants for uniformity, so that plants can be ordered to a standard type.

These may well be grown via vegetative cloning (grafting, cutting), from cultivars to keep similarity in form.

For planting such as shelter belts, woodland, from seed would be cheaper, if form is less of an issue.

Nursery stock 

Nursery stock can be either 

Bare root 

Rootball 

Container grown 

Bare root 

These are supplied with no soil, so are lighter. When planting a slurry gel applied to the roots can keep them moist. 

Plants with only thick, non-fibrous roots should be rejected. 

Rootball 

These are field grown then removed with a cutting machine. They’re stored before delivery, either in co-extruded bags (white on the outside, black on the inside – to exclude light and retain moisture. 

They may also be stored in plunge beds. 

Container grown 

Container grown stock will not have the soil benefits of field growing (such as associations with microbial life and fungi. 

There is the likelihood of roots growing in a ring that needs checking for. These, again, should be rejected.