For the majority of the criteria grading standards and measures have been developed and accepted for the usual specifications of trees. However in some instances it may be necessary to specify other details. The following is a list of some of the more typical extra specification requirements which might be used. They should be considered to be indicative and not comprehensive.
Origin and Provenance
These terms are of particular importance in the specification of native (indigenous) plants, or plants which are required from a known source of propagation material. Origin is defined as “the place in which indigenous plants are growing or the place from which non-indigenous plants were originally introduced.”
Provenance is defined as “the place in which any plants, whether indigenous or non-indigenous are growing.”
It is inappropriate to specify particular origin/provenance speculatively. A limited number of specialist growers are producing native species and may be listed as sources. Specifications should be developed following discussions with specialists (ecologists and growers) and then contract grown to precise requirements. It is more straightforward to specify the required provenance (indicating the exact source of the young plants or propagation material) if this is significant to the project.
Current British Standards indicate that the ‘country of origin’ is the country where the plant has been growing for the latter half of the most recent growing season. If this is not acceptable then it may be necessary to require information about the provenance of the propagation material (seed, cuttings, budwood, grafts, etc.) in the specification.
Top or Bottom-working
Many cultivar or clone forms of commercially available trees are vegetatively propagated by budding or grafting. In the UK, most trees are ‘bottom worked’, budding the desired cultivar or clone onto a transplant of a related species, close to ground level, e.g. Sorbus aucuparia ‘Sheerwater Seedling’ budded onto the rootstock of Sorbus aucuparia grown from seed. The bud is then trained to form the stem and crown of the desired cultivar.
‘Top working’, grafting the desired form at high level (typically 1.6 metres or higher) is not encouraged in this country except for certain weeping trees although it is more commonly used as a means of propagation throughout the rest of Europe.
All trees should be bottom worked unless otherwise specified.
The Summary of Specification Criteria indicates the natural or most typical forms in which trees can be bought. However there are other shapes of trees and the following gives some examples of the more common types:
These trees, typically genera Tilia and Platanus, are trained to provide an instant pleached effect. Although mature pleached trees may be trained to form a three dimensional ‘hedge on sticks’, (typical for Carpinus betulus, for example), commercially available pleached trees tend to have a two dimensional effect with the branches spreading sideways in one plane only.
These trees, typically genus Salix, have a minimum clear stem height of 2 metres and a head which has been cut to create a head of the typical pollard regrowth.
Popular in continental Europe for providing shade, these large trees have had their central leaders cut and the main branches trained over a horizontal frame, creating a parasol effect. Tilia and Platanus are typical genera used to create these shapes.
Espalier and Fan
An espalier is a tree with a central stem with balanced, (i.e. the same number) of horizontal branches in one vertical plane on each side, the bottom tier being 30-40 cm from ground level and additional tiers spaced 30-40 cm apart. The branches as the same level must be about the same length and size.
A fan is a tree with a leg not more than 50 cm in height and a balanced fan-shaped system of branches in one vertical plan, with a minimum of 5 branches at least 30 cm long. Shoots must have about the same length and size
These are typical for top fruit trees (Apples, Pears, Plums). Whilst these trees can be trained from maidens, two tier espaliers are available commercially. Many other shapes (Horizontal cordon with one arm, Horizontal cordon with two arms, Oblique Palmet, Single Stage Oblique Palmet, Two-Stage Oblique Palmet, Single U, Double U, and Two Stage Double U) are also available. Consult specialist growers for more details.