Here at North Willamette Research and Extension Center, we recently established a research plot of blueberries like no other. The plant could be attractive to both growers in its architecture and homeowners in its aesthetic appeal. They are single-stemmed blueberry “trees.”
Blueberry trees have vast potential for commercial growers. Many commercially grown blueberries are picked by machine for the processed markets. The picking machine has catch plates running along the base of the plants and collects berries as they are knocked off the bush by the rotary or sway heads. Because standard blueberries have many shoots arising from a broad base, these catch plates cannot close entirely and many berries fall through onto the ground. Growers can loose up to a quarter of their crop to ground loss. A single-stemmed blueberry tree would cut these losses dramatically.
Cultivating a blueberry tree involves grafting a common, commercial variety of blueberry onto a rootstock that has been trained to contain only one stem. The rootstock is a berry plant native to the southeastern United States called sparkleberry or Vaccinium arboreum (the name “arboreum” alludes to its common habit of growing like a tree).
Because there is no commercial rootstock for blueberries, the first step to create a blueberry tree involved growing the sparkleberry by seeds and choosing straight, tall plants for grafting trials. When the sparkleberry seedlings grew to about pencil size in diameter, we grafted three common commercial blueberry varieties ‘Draper’, ‘Liberty’ and ‘Aurora’ onto these rootstocks by a whip-tongue grafting technique. The success of these grafts led to the establishment of a field research plot.
Now that we know grafting of blueberries is a possibility, there are many more questions to answer: What will be the success of grafts over time? Will the rootstock affect the quality of the berries (the firmness, sugar levels, ripening date)? Does the success of the grafts change by variety? Does the rootstock change the soil requirements for cultivation?
These questions are being examined in our test plot. Growing side-by-side are the three varieties both grafted and non-grafted, in two types of soil treatment (sawdust-amended and native). The first growing seasons showed much potential for the plants, both in survival, new growth and berry production. And the oncoming seasons will find us busy with countless data collections to help us answer many questions.
Refinement of the growing process continues as well. Seedling trials have helped us identify potential rootstock candidates, which are now being propagated by tissue culture. We are exploring grafting techniques and timing to make the plants most easy for growers to propagate. In the future, one might find these grafted blueberry trees growing on acres of farmed land, or perhaps as a novelty blueberry plant grown in a home garden.
Author: Adrienne Basey