Cherries and quality, also in relation to the theme of increasingly challenging climatic conditions for cherry growing: these topics were also covered during the latest edition of the ‘Stone Fruit Day’ organized by Washington State University (WSU) , which took place last January 22 and was followed live remotely by Cherry Times.
In particular, Bernardita Sallato, a researcher at the Irrigated Agriculture Research and Extension Center (WSU) in Prosser, focused on the topic of cherry tree nutrition; Carolina Torres, Associate Professor in Postharvest System (WSU), presented the results of a study focusing on the need to extend shelf life while maintaining quality, exploring the link between storage and weather conditions during the production season; Jonathan Magby, Department of Horticulture (WSU), delved into the topic of the dormancy of cherry trees related to climate change.
Cherry tree nutrition is becoming even more central, as cherry orchards, including those in the U.S. and specifically in Washington State, are increasingly exposed to highly stressful climatic conditions.
“Nutrients are essential, and the limitation of any of the elements necessary for the plant either causes tree death or leads to poor fruit quality or failure to maximize production and fruit quality,” Bernardita Sallato immediately clarified. The researcher then explained how to calculate the actual needs of the cherry tree under given conditions in a specific orchard.
First, it is necessary to assess the current situation through testing and analysis to determine the concentration of elements. To do this, the right leaf is collected. Here, at this LINK, you can find a detailed article by Bernardita Sallato on how to conduct and interpret analyses, as well as the standard ranges of various elements for cherry trees.
It is important to highlight that, regarding fertilization and the addition of necessary elements, the benefit curve for tree health follows a bell shape.
This means that the cherry tree will respond only up to a certain point; once a specific level on the curve is reached, fertilization should stop because the ideal concentration has been attained. Increasing the dosage of a certain element beyond this point will not yield additional benefits; on the contrary, exceeding a certain threshold leads to toxicity, damaging the plant.
Response of the cherry tree to nutrient supply. The red line refers to nitrogen inputs, and the green-highlighted box refers to the optimal supply. Source: slide presented by B. Sallato during the ‘Stone Fruit Day’ 2025 at WSU.
“Beware,” Sallato warned, “that for certain elements, such as nitrogen, the bell curve is narrow , so the transition from deficiency to toxicity occurs very quickly. The curve shows that only in cases of an element deficiency will its addition provide benefits in terms of fruit quality, size, or yield.”
How, then, to calculate the amount to supply to the orchard for different elements and how to optimize nutrition? The formula seems simple, but obtaining the necessary data is more complex: the required amount of a given element must be adjusted based on supply and divided by efficiency, which must be taken into account. One of the goals is certainly to increase nutritional efficiency.
Bernardita Sallato reviewed the main macro and microelements, with a particular focus on nitrogen. Depending on the cultivar in question, nutrient requirements will vary, also depending on the orchard's location. The WSU team has developed a table specific to Washington State, referring to a production of 1 US ton, equivalent to 0.91 metric tons.
Annual average nutrient requirements for cherry trees (N, P, K, Ca, Mg, S) expressed in pounds per US ton of cherries. Ranges are calculated based on the cultivation area in Washington State (USA). Note: 1 US ton equals 0.91 metric tons, 1 pound equals 0.45 kg. Source: slide presented by B. Sallato during the ‘Stone Fruit Day’ 2025 at WSU.
Once the nutrient needs for a given production level are established, the next step is to calculate the amount of a specific element to supply: “To determine how much nitrogen needs to be provided, for example, factors such as soil composition, irrigation (based on analysis), and whether pruning material is incorporated must be considered. The nitrogen supply must take everything into account, and often, without realizing it, irrigation alone already introduces many elements.”
For water, nutrient levels can be determined relatively easily through analysis, but it is more complex to assess how much is supplied to the soil, particularly for nitrogen, which is highly mobile: “I want to emphasize that nitrogen exists in many forms and that there are many potential losses throughout the season. For example, volatilization, denitrification, and leaching. Leaching is the most significant, especially in sandy soils, as found in several areas of Washington. Because of these losses, soil analysis is not a reliable method for estimating nitrogen availability in the soil,” the researcher explained.
“For other elements that are more stable, all we need to do is a soil analysis to maintain levels within a given range."
"However, it is crucial to consider soil structure, which is fundamental for interpreting results.” Regarding micronutrients, Bernardita Sallato emphasized the importance of boron: “This micronutrient can become unavailable in high soil pH. It is also a very limited mobility element that depends on the tissue, the time of year, and the development stage. Boron is crucial at certain phases—new cell growth relies on boron—which is why we must apply boron before flowering.”
Here is a summary of Bernardita Sallato’s presentation at the Stone Fruit Day 2025:
Carolina Torres, Associate Professor in Postharvest System (WSU), focused on the links between climate change and maintaining postharvest quality, also to extend storage duration. “My research focus on cherries is driven by industry needs,” said Torres. “Firmness is important, the stem should remain green, and the storage should last longer. These are the key topics of interest, and I know that by studying them, I can make an impact.”
Torres conducted her research over three seasons, from 2022 to 2024, though data was also collected in 2021. The cultivars studied were Rainier, Bing, Skeena, and Sweetheart from commercial orchards. The cherries were cooled to 1.11°C immediately after harvest and then stored at 0°C in controlled atmosphere packaging (MAP Bag) for 30 days, as this was the research goal.
In the 2022 and 2023 seasons, cherries were harvested both at commercial timing and several days earlier.
Spring-summer weather patterns over the four seasons considered in the trials at two locations in Washington State. The dates on the X-axis indicate month/day. Source: slide presented by C. Torres during the ‘Stone Fruit Day’ 2025 at WSU.
Carolina Torres highlighted how the different seasons in Washington were profoundly different: “In 2021, we experienced that extreme heat wave in June, around the last two weeks. In 2022, we had a very low spring temperature during bloom, with 5°C around that period, followed by a cool spring-summer, making it a rather cold year.”
In 2023, summer was warm compared to the previous three years, but we had a good bloom period with cool temperatures. In 2024, during bloom, it was very hot, even warmer than in 2023, but later, it was cooler than the previous year. May and June were much colder compared to 2023. The data refers to the Mattawa and Othello areas, where the commercial trial blocks are located,” she explained.
The research monitored, at 15 and 30 days post-harvest, the color evolution of the stem and its strength, the intensity of red (for red varieties), the Brix level , and the firmness of the flesh. Some of the findings from the data comparison: regarding the stem and its ability to resist browning, “2021 was a highly stressful season for all varieties, resulting in very brown and dehydrated stems, and this characteristic worsens with longer storage.”
Thus, even if the fruit is harvested with good parameters, it cannot be stored for long. Another observation: harvesting before the commercial date does not always yield better results, as there is no strong correlation, and this holds true for most varieties. Regarding stem strength, no major changes were observed during storage.
It is generally believed that cherries will eventually lose their stem, but a 30-day storage period may not be enough to observe this. In a year when stem strength was already low at harvest, the stem detaches more easily. Take 2023, for example—what happened that year? Thirty days before harvest, temperatures were higher than in the other years studied, which may have had an influence.
Regarding red color, it appears to remain stable during storage; in some cases, commercial harvest produced more intense coloration than early harvest. Analyzing firmness, the measurement results suggest that cherries do not soften over time, but we know this is not the case. Simply put, firmness measurement is not a good metric. Firmness is measured only in the outermost millimeters.”
Carolina Torres’ research continues, but reaching initial conclusions, she stated: “Harvesting at the correct maturity stage is crucial for prolonged storage. I will continue to investigate the effects of environmental stress and climate on stem conditions.”
And the changing climatic conditions were also the focus of Jonathan Magby from the Department of Horticulture (WSU), in his presentation titled: “Varying Cold Hardiness of Sweet Cherry Cultivar.” Introducing his research, Magby said: “Cold tolerance, bloom timing, and dormancy interact and play a key role in plant survival and growth.”
Dormancy also influences the flowering capacity of sweet cherries and many other crops. The dormancy mechanism is central to survival during winter periods, triggered by cold temperatures in autumn and shorter days. The flowering and growth phases, on the other hand, are driven by warmer temperatures and longer days.”
He then observed: “In recent years, frost and frost damage have proven to be major threats to production, and the situation does not appear to be improving in the coming years. Additionally, bloom is occurring earlier , increasing susceptibility to spring frosts.”
For Magby and the WSU team, understanding dormancy mechanisms is crucial: “Understanding dormancy and its progression is related to cold tolerance during the acclimation period and its maintenance leading into the flowering phase.”
Jonathan Magby’s presentation during ‘Stone Fruit Day’ 2025, WSU
The research team collected a dataset over three years, from 2019 to 2021, analyzing cold tolerance during endodormancy and ecodormancy in 29 cultivars. They monitored dormancy using a unique method developed by WSU, tracked plant growth, gathered data on bloom timing for different cultivars, and monitored water content in buds. Additionally, they selected six highly cold-tolerant varieties and six susceptible ones.
Among the key findings highlighted by Magby: “The results show that winter cold resistance does not necessarily mean the variety is also resistant in spring. Interestingly, varieties with poor winter cold tolerance that suffered damage experience 30-40% less damage if they make it past October when facing spring frosts.”
Additionally, cold-tolerant individuals have a higher acclimation rate when developing dormancy compared to susceptible ones. Those with a high chill requirement also remain in endodormancy for a longer period. Monitoring the water content in buds, we found that a relatively higher water content in cold-tolerant individuals provides some support for greater cold tolerance during winter.”
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Cherries and quality, also in relation to the increasingly challenging climatic conditions for cherry growing: these topics were developed among others during the latest 'Stone Fruit Day' organised by Washington State University (WSU).
