The Root system must be well developed by good nursery practice influenced by the natural characteristics of the species/cultivar taking into account its age and growth rates under the cultural and soil conditions within which it is growing. The system must not show any coiled mains roots close to the collar, nor any physiological damage.
The root system must not be allowed to dry out at any time.
Plants can be supplied in four root conditions:
- bare root (bagged)
- rootballed (balled and wrapped)
- container grown
- cell grown
Typically the smaller sizes of trees and those species which transplant more readily will be supplied bare root. All bare root systems must be supplied in bags, containing and enclosing the whole root system and tied at the top. The bags used should be manufactured from co-extruded polythene – black on the inside and white on the outside. Seedlings, cuttings and transplants (up to 30-40 cm, Overall height) are typically supplied with shoots and roots fully enclosed in the bag, whereas for larger trees only the root system is enclosed. Trees should be bagged in the field immediately upon lifting.
Trees will be supplied bagged unless any other protection (rootball, container grown) for the root system is specified. All evergreen broadleaf trees are supplied rootballed or container grown. Deciduous trees with girth measures greater than 18 cm should be specified as rootballed.
Rootballs must be firm and solid and the roots must penetrate the whole ball. They must be enclosed in hessian (burlap). The size of the rootball must be appropriate for the species/cultivar and its age and growth rates under the cultural and soil conditions within which it is growing. The root ball must be free of perennial weeds. Rootballed trees are indicated by the letters ‘‘RB’’ in the plant specification.
For Standard trees of girth 12-14 and larger and the equivalent sizes of multi-stemmed and bushy trees, the root ball will be additionally protected with ungalvanised wire netting or wire basket. All materials used to support root balls must decompose within eighteen months of planting and not constrict the continuing growth of the tree. Root control bags can be used instead of RB.
Container grown plants should have been grown in the container for sufficient time for the root growth to have substantially penetrated the medium but not be root bound.
Container-Grown (Pot-grown) Trees
Plants are to be centered in the container, well rooted, firm and moist on delivery, with the growing medium coming within a suitable depth of the pot rim. The surface of the growing medium shall be free of all weeds.
The following containers are commonly used:
- rigid containers
- spring ring/airpots
- easy-lift bags
- polythene bags
- custom-built containers for very large trees
Cell grown trees, which are usually seedling in form, combine growing the plant in a container (a cell) and then supplying the plant as a complete root ball, bundled together, protected with plastic and supplied in boxes.
Cell trees are specified by ROOT VOLUME (Container size), HEIGHT and ROOT COLLAR DIAMETER.
As with all plants, specifications cannot be rigid since growing conditions will vary from year to year but the information in this specification gives the general standards for growing cell plants. Again, as for other stocks, larger plants can be grown by contract.