The last few times I have traveled to the fruit growing regions of the Pacific Northwest (PNW) of the United States, I was struck by an interesting juxtaposition. Young apple orchards with narrow, trellised rows of single- or double-stemmed spindle trees spaced about 2 feet apart were predominant. Often these can be adjacent to young orchards of similar sweet cherry trees with wide rows of Steep Leader trees to multiple leaders spaced 8 to 12 feet or more apart.
What a contrast! The less laborious small-fruited (cherry) species is still cultivated as a tree requiring a ladder for harvesting, and the larger-fruited (apple) species is cultivated to be harvested by workers on a platform or, in some testing now, even by a robot.
This surprised me, as I was fortunate enough to work in Yakima Valley at Washington State University At the end of the last century, when the newly available dwarfism, early cherry rootstocks hinted at visions of future cherry orchards that would be more easily harvested from the ground. Granted, these visions have been realized by some producers over the past 20 years, but not as much as I would have imagined now. Why?
HAPPY AS IS
Well, it is clear that the sweet cherry growers in PNW have continued to make a lot of money over the past two decades with large trees that produce high annual yields of large fruit. Compared with many cherry-growing regions, the arid and sunny climate of eastern Washington State presents a relatively low risk of spring frosts and heavy rains during ripening, a relatively low incidence of disease and pests that are expensive to manage, and relatively abundant and skilled (albeit increasingly expensive) to harvest.
In the early 2000s, early commercial users of vigor-limiting rootstocks also expressed concerns that they were causing inherently smaller fruit size. However, extensive research and grower experience has clearly shown that small fruit size is a function of harvest load management – maintaining the proper balance between leaf area and number of fruits. Late summer and fall nutrition is particularly important for cherry trees on vigorous-limiting rootstocks in order to build up nitrogen and carbohydrate storage reserves, which influence flowering and leaf development the following spring. . Large spur leaves are essential for obtaining large fruit.
In cherry growing areas other than PNW, where rain cracks more frequently and endangers market supply (and revenue consistency), the future orchard business plan may require a strategy to exclusion of rains. In this case, smaller and precisely structured trees make it easier to install and maintain protective covers, and earlier yields on early rootstocks speed up loan repayments for such investments.
Likewise, when the labor (skilled or otherwise) to harvest is less abundant, or may become less abundant in the future due to political issues, or may become more expensive in the future due to issues societal, the large potential gains in labor efficiency with and more specifically structured trees are likely to be increasingly important factors in the profitability of orchards during the 1920s.
ANALYZE YOUR SITE
Additional considerations typical against smaller cherry trees include concerns about a higher proportion of the crop closer to the ground and, therefore, exposure to colder air during radiative frost events, and poor performance. of some dwarf rootstocks under high and stressful summer temperatures, or on shallow, sandy and rocky soils. Therefore, site selection for good air drainage and frost risk mitigation strategies, such as wind turbines, are indeed important elements for planning small orchards made with gateways. dwarf grafts or training systems.
Likewise, orchards should be located on more fertile soils if dwarf rootstocks are to be used. Denise and Gerry Neilsen, scientists at Agri-Food Canada, clearly demonstrated that high frequency, short duration irrigation and fertigation packages can dramatically improve tree performance on dwarf rootstocks. Small trees have small root systems and therefore frequent supply of small amounts of water and nutrients most effectively optimizes daily photosynthesis and leaf function to continuously supply developing fruits with carbohydrate and pressure. turgor necessary for growth.
Conversely, if the orchard site is defined by soils with low nutrient and water retention capacity, or high summer temperatures, an orchard on a semi-vigorous to vigorous rootstock should be expected. Such cherry rootstocks develop more extensive root systems, providing greater “buffering capacity” against daily transient water stress which can stop photosynthesis and thereby limit fruit growth.
When soils are fertile and high summer temperatures can be stressful, a vigorous rootstock should be combined with a vigor-diffusing training system if the business plan calls for a small, precisely structured and efficient labor force will be the most profitable for the next two decades or more. Suitable drive systems include the KGB (Kym Green Bush) for diffusing vigor in non-trellised three-dimensional pedestrian orchards that can be picked without ladders, and UFO (vertical fruiting branches) for the diffusion of vigor in highly structured two-dimensional (plan) trained orchards which facilitate the partial mechanization of certain pruning, training and harvesting tasks.
Cherry Rootstock and Training Decisions: Thoughts for the 2020s