Preparing a cherry orchard for dormancy involves several key phases. In cherry trees, the period from flowering to harvest is relatively short, lasting only 45 to 70 days, making it shorter and more intense than many other deciduous fruit trees. After harvest, the trees remain active for an extended period, undergoing various physiological processes to support the growth of different parts, such as roots, shoots, and buds, while also getting ready for the winter dormancy.
In the post-harvest phase, cherry trees continue to produce carbohydrates through photosynthesis. These carbohydrates are crucial for immediate metabolic needs, as well as for the growth of roots, shoots, branches, trunk, and the development of buds. Some of the carbohydrates produced are stored as reserve compounds, primarily starch and arginine, which will later support bud development in the next growing season. Therefore, during this period, it’s crucial for growers to minimize stress on the trees to maintain high photosynthetic activity and ensure the long-term productivity of the orchard.
Here are the main events that cherry trees go through in the post-harvest phase, along with recommended management practices to prepare the orchards for dormancy:
Root Growth: After harvest, cherry tree roots experience rapid growth, followed by another peak in growth just before the leaves fall. The length and branching of the roots during this period directly impact the tree’s ability to absorb water and nutrients. More extensive root development also leads to greater starch accumulation, which supports fruit development in the next flowering season and reduces fruit loss. Additionally, increased root branching provides more endogenous cytokinins, which promote future fruit growth.
Floral Induction and Differentiation: In the weeks around harvest, buds undergo floral induction for the following season. This process involves biochemical changes within the buds, transitioning them from a vegetative to a reproductive state. Induction is triggered by changes in day length, hormonal balances, and stress levels, leading to multiple genetic responses that ultimately result in irreversible floral differentiation. During this phase, buds develop into full-fledged floral organs (Figure 1). Buds that do not undergo induction continue their growth as vegetative structures and will produce new shoots.
Acclimatization for Winter Dormancy: As the orchard transitions to winter, cherry trees enter a dormancy phase, temporarily suspending meristematic and circulatory activities to adapt to colder winter conditions. This dormancy phase involves various biochemical and hormonal changes within the buds, including reduced respiratory rates, decreased tissue moisture, and hormonal suppression of bud growth. Dormancy varies for each bud and generally begins in the summer, progressing from the base to the tip of the twig. During dormancy, buds experience “endodormancy,” a phase where bud growth is inhibited due to factors within the bud, such as prolonged exposure to low temperatures. Subsequently, buds transition to “ecodormancy,” where bud growth depends on external factors like photoperiod, temperature, and water availability. Buds will not grow until favorable environmental conditions return. Additionally, some buds may be in a “paradormant” state, meaning they cannot sprout due to internal plant conditions but are affected by different factors, such as apical dominance from the terminal bud.
Exit from Dormancy: The exit from dormancy begins when cold requirements are met, and environmental conditions become favorable. Various models have been developed to estimate when bud break will occur based on the accumulated cold exposure perceived by the trees (Figure 2). Cold requirements can differ between cherry varieties and depend on growing conditions.
In addition to these phases, post-harvest orchard management is critical for supporting tree health and preparing for dormancy. This management includes:
Irrigation: The need for irrigation remains high until the end of August, varying by region and based on Reference Evapotranspiration (ET0). It’s crucial to start with 100% of ET0 (Kc=1) and gradually reduce it to 50% by mid-September. This gradual reduction helps signal the plants to enter dormancy. In challenging conditions like rocky soils, dwarf rootstocks, or hot weather, it’s advisable to use micro-sprinkler irrigation instead of drip irrigation. This improves the orchard’s microclimate, raising humidity and lowering ambient temperature.
Mineral Nutrition: Post-harvest mineral nutrition influences next season’s tree and fruit growth. Nitrogen application should consider rootstock vigor and fruit growth duration. For potassium, apply 80% from fruit set to harvest, with increased application after fruits turn straw-colored, and the remaining 20% post-harvest. Apply phosphorus: 50% between full bloom and petal fall and 50% during post-harvest root flush. Micronutrients like boron and urea should be sprayed in late summer (September-October) to support pollen tube growth during the next flowering. Recent research highlights the importance of Molybdenum and Manganese for lignification and dormancy entry. Consider post-harvest applications of formulated products like Zinc-Manganese and Boron-Molybdenum.
Soil Amendments: Optimal timing for soil amendments like manure or compost is fall and winter. This enhances soil texture, structure, moisture retention, and buffering. You can supplement amendments with calcium, using calcium sulfate for neutral pH soils or calcium carbonate for acidic ones. Additionally, apply ample potassium sulfate, chloride, or potassium oxide if soil potassium levels are below 200 ppm. This helps improve soil structure and contributes to fruit nutrition.
Reducing Environmental Stress: To sustain orchard productivity, manage cherry tree stress. High solar radiation in late spring and summer can harm plant tissues, disrupt photosynthesis, and affect stomatal closure. Similarly, high temperatures and radiation in July and August can lead to fruit anomalies in the next season (Figure 3). Apply solar protectants like kaolin post-harvest to reduce stress, boost photosynthesis, encourage root starch accumulation, and minimize issues during floral differentiation.
Phytosanitary Management: After the harvest, it’s essential not to neglect the health aspects of the orchard, as several pests and diseases can invade the trees during this period. It’s also a good time to clean up cankers, taking advantage of the low relative humidity.
For weed management, keep live grass between tree rows to lower orchard temperature, assuming that there’s enough water. Conversely, keep row strip areas weed-free to prevent competition with trees for water and nutrients.