Cherry orchards are in full dormancy; ideally, since the end of April, beginning of May, these structures began their winter lethargy represented by the fall of at least 50 percent of their leaves; always considering that yellow leaf equals fallen leaf. “Ideally” is indicated because sometimes and due to different factors, strategies must be used to shed leaves and thus begin dormancy.
This winter dormancy is essential, as during this period the plants “rest” and metabolise their reserves to begin a new development season. During these months (May-June-July) special attention is paid to the accumulation of chill hours (CH), which in cherry trees occurs between 1 May and 31 July. A good accumulation of chill, according to the specific requirements of each variety, is the main indicator of dormancy, as it can be concluded that the plant uses its reserves better if it meets the CH requirements.
But there are also other components that are often overlooked, but which have a significant impact on dormancy. Rain directly influences the winter dormancy of plants, since the more days they are wet, the better the cold storage will be for the structures.
On the other hand, a very relevant factor in terms of dormancy is the length of the day or darkness; it is worth mentioning that the first hint of dormancy occurs with the beginning of summer and the shortening of the photoperiod. This shortening causes the annual materials of the plants that grow from the end of December and that develop for about 70 days to present lignified basal sections, which affects the induction of flowers, accumulation of reserves, change of sap flow and the beginning of preparations to start dormancy.
In short, wetter winters are probably also darker winters with shorter photoperiods, and that is an important component of dormancy.
But is it possible to determine whether these factors, or the accumulation of more cold hours, can ensure the success of the season in terms of optimal production conditions? The answer is definitely no.
This topic requires a more technical analysis. When we are facing a winter like this, it is often said that there could be poor dormancy, because there may be less accumulation of HF; however, this could change if rainfall and photoperiod are considered as important factors in the quality of the dormancy period.
On the other hand, it must be considered that the accumulation of cold is extremely important in endodormancy, which is the central part of dormancy, with June and up to the first week of July being the main period of this stage. During endodormancy, plants must accumulate at least 40% of the total HF requirement, therefore, there are many more factors or many more indicators that must be considered or measured to evaluate whether or not it is a good dormancy, keeping in mind that the condition of this winter lethargy, its quality, will be one of the indicators or factors of production.
Clearly, neither the cold hours, nor the rain, nor the photoperiod define a season, as there are other factors that affect cherry production. For example, in years with very good dormancy, but a poor accumulation of degree days in spring, the normal development or metabolism of the plant is affected in terms of developing floral structures or fruiting, which could end in a bad year.
On the other hand, if dormancy is not so good, perhaps a very good spring, sunny days, with good relative humidity, would be enough to balance this out, so that all the pollination and fertilization processes take place and to have a good setting and a good result in terms of productive potential. Therefore, it must be kept in mind that these are factors that do not entirely ensure a successful season or a bad season.
Each season is different and has its own characteristics. The important thing is to have as much current information as possible, as well as information from previous years. This allows for comparison, evaluation and informed decision-making in order to achieve the productive potential of the orchard.
