Creating a Tree Cultivar:
Nurseries are continually looking for and developing trees that will grow in that gap between the forest and the city. By manipulating a tree's special genetic characteristics, tree nurseries develop, select and grow variations on these natural trees that show distinct characteristics including pest resistance, flower and fruit production, drought tolerance and desirable form. These trees are often called cultivars and a product of man's manipulation.
Tree Cultivar Vs Tree Variety:
On the other hand, cultivars are not necessarily true to type and do not have the ability to sexually reproduce consistently. In other words, cultivar means "cultivated variety" and trees have been selected and cultivated by tree lovers, botanists and nurseries for centuries - that's a cultivar, an artificial label of love.
Problems With Developing a Cultivar Sexually:
To actually propagate accurate clones, many cultivars must be propagated vegetatively through cuttings, grafting, and even tissue culture. While propagation by seed is unpredictable and usually results in something different than the parent tree, cultivars break the natural code and allow diversity.
Developing a Vegatative Cultivar:
"Cutting" is the most common of vegetative propagation methods. A part of the "parent" plant is cut off and placed into a misted soil medium conducive to root sprouting. Adventitious roots are generated from stem and leaf cuttings and certain species of trees can do this extremely well (willow, fig, yellow poplar).
"Grafting" or budding is a very effective form of asexual propagation and a nursery standard. A stem piece or a single bud called the scion is joined on to rootstock. This rootstock is a hardy, easily produced tree, usually of the same species as the desired cultivar.
The Cultivar Business:
There is a staged process in the production of tree cultivars and three types of nurseries may be involved - the propagator, the primary grower and the larger caliper tree grower. Some nurseries do all of these stages of production, other specialize and limit themselves to one or two stages.
Types of Tree Nurseries:
The primary grower takes the tree growing process a bit further and produces a tree with a root ball ready for planting. They also do the secondary propagation when grafting or budding a cultivar onto a seedling rootstock is necessary. These trees range from unbranched 4’ “whips” to 15’ tall branched plants.
The caliper grower takes trees grown by a primary grower and produces a larger sized tree to a 2” to 8” trunk diameter. These larger trees are usually planted on city and large commercial landscape projects and take 2 to 8 or more years to develop.