Root collar diameters may be given in specifications of conifers, especially seedlings and transplants used in forestry planting, since they assist in quantifying the ‘substance’ of the plant.
Girth measures are seldom used, but are a useful measure especially for Pinus spp. which can be grown to semi-mature size with a clear stem.
Root Collar Diameter
The Root Collar Diameter is defined as “the diameter of the main stem measured at or within a specified distance from the root collar.” The root collar is between the base of the aerial part of the plant and the top of the root system.
The Root Collar Diameter may be specified for seedlings (especially cell grown trees) and transplants, particularly where these are used as rootstocks or for forestry purposes.
Cell grown conifers
For cell grown trees, minimum Root Collar Diameters vary from 3 to 8 mm for Conifers, depending on overall height and size of cell.
|Root collar diameter||Overall height (cm)||Volume (cc)|
Seedlings and Transplants – open-ground
For Seedlings and Transplants, Root Collar Diameters will be a minimum of 3 mm and be graded in one or two mm bands, increasing with height and species, e.g. 3/4, 4/6, 6/8, 8/10 or 10/12. This table indicates some typical root collar diameters for open ground forestry conifers:
|Height (cm) no less than|
|Species||Minimum root collar diameter (mm)|
|Chamaecyparis lawsoniana, Thuja plicata||n/a||n/a||n/a||4||4.5||5||6.5||7.5||6.5|
|Larix decidua, L. eurolepsis, L. kaempferi||n/a||n/a||n/a||2.5||3.5||4||5||6||9.5|
|Pinus nigra maritima||3||3||4||4.5||5.5||6.5||8||9.5||n/a|
Seedlings and transplants – container-grown
Increasingly, coniferous forestry seedlings are grown in cells. However, if they are grown in other containers, the following root collar diameter grades apply.
|Minimum height||Min. root collar diameter||Minimum container size|
|Pinus nigra maritima||12||2||100|
The girth of a tree is “the circumference of the stem measured at 1 metre above ground level.” For Semi-Mature/Specimen conifers with clear stems, girth measures are indicated in the same ranges as for broadleaf trees, but it is important to note that height grades are different, namely: 18-20cm; 20-25cm; 25-30cm; 30-35cm; 35-40cm; 40-45cm; 45-50cm; 50-60cm.