Cherry fruit development transforms a delicate spring blossom into a fully ripened stone fruit. Botanically classified as a drupe, the cherry belongs to the genus Prunus, which also includes peaches, plums, and apricots. Commercial cherries are primarily derived from two species: sweet cherry (Prunus avium), which is typically eaten fresh, and tart or sour cherry (Prunus cerasus), which is generally used for cooking and preserves.
The Cherry Tree’s Annual Cycle
The progression of a cherry from flower to fruit is governed by the tree’s annual cycle, which begins with a requirement for cold temperatures during winter dormancy. This period of rest is triggered by leaf fall in autumn, signaling the start of the chill accumulation phase. Cherry varieties have high chilling requirements, with most needing between 800 and 1,200 hours of temperatures between 32°F and 45°F (0°C and 7.2°C) to properly reset their biological clocks.
If the tree does not receive sufficient chill hours, its hormonal balance is disrupted, leading to uneven bud break and delayed flowering in the spring. Once the cold requirement is met and spring temperatures rise, the buds begin to swell and burst, moving quickly through stages like “early white” and “white bud” before reaching full bloom. Sweet cherries typically bloom earlier than tart cherries, but for all varieties, the bloom time is the narrow window when the tree is ready for fertilization.
Pollination and Fruit Set
Pollination involves the transfer of pollen grains from the anther to the receptive stigma of a flower. For cherry trees, this is primarily an entomophilous process, relying heavily on insects like honeybees and bumblebees to move the pollen between flowers. Once a pollen grain lands on the stigma, it hydrates and germinates, growing a pollen tube that travels down the style to reach the ovary.
Most sweet cherry varieties are self-unfruitful, meaning they require cross-pollination to produce fruit reliably. Tart cherries, in contrast, are largely self-fertile, capable of setting fruit with their own pollen, though their yields improve with a nearby pollinator. Successful fertilization within the ovary leads to “fruit set,” where the unfertilized flower part, known as the calyx, begins to swell, and the initial, tiny fruitlet forms beneath it.
Stages of Cherry Maturation
Following the initial fruit set, the tiny green fruitlet undergoes three phases over approximately 55 to 90 days until harvest. The first phase is characterized by rapid cell division, which establishes the maximum potential size of the cherry. During this time, the fruit remains small and green as it focuses on building the fleshy mesocarp tissue.
The second phase is an apparent pause in external growth, during which the fruit’s internal resources are dedicated to pit hardening. The endocarp, the innermost layer surrounding the seed, synthesizes lignin, turning the soft inner shell into the hard stone characteristic of a drupe. The final phase of maturation involves a second burst of exponential growth, but this time it is fueled by cell expansion, not division.
During this final swell, sugars are accumulated, and pigments develop in the skin. The cherry rapidly transitions from green to yellow, then to bright red, and finally to a deep mahogany or black color, depending on the variety. This period is when the fruit gains its characteristic flavor and juiciness, marking the completion of the biological process.
Harvesting and Ripeness
Cherries are classified as non-climacteric fruit, meaning they do not continue to ripen or increase in sugar content once they are picked. Therefore, the timing of harvest is precisely determined by indicators of peak ripeness, which include color, firmness, and maximum sugar accumulation. Sweet cherries, which are sold fresh, are typically hand-picked with the stem attached to maintain freshness and prevent fruit damage.
Growers use a taste test and color charts to ensure sweet cherries have reached their full dark red or mahogany hue, as the sugar content significantly increases in the final few days. Tart cherries, which are primarily grown for processing, are harvested differently: their ripeness is signaled when they easily separate from the stem, allowing for mechanical harvesters to gently shake the fruit off the tree. The entire harvest window for a specific variety is typically short, lasting only two to three weeks, requiring efficient collection to capture the fruit at its optimal quality.