The peach (Prunus persica) is a valued fruit whose appeal lies in its summer availability. Understanding when peaches grow involves tracking the progression from a dormant tree to ripe fruit, a cycle that spans three to five months following the first blooms of spring. This growth is governed by genetic programming and environmental factors, which determine the precise timing of the harvest.
The Spring Transition: Flowering and Initial Set
The peach tree’s annual cycle begins after winter dormancy, which requires accumulating “chill hours” (hours below 45°F or 7°C) to prepare flower buds for spring growth. Once this requirement is met, rising temperatures trigger bud swell, leading to the appearance of blossoms in late winter or early spring. This flowering stage, marked by fragrant pink blooms, is delicate and typically lasts only one to two weeks, making it highly susceptible to damage from late frosts.
Successful pollination, often by bees, signals the transition from flower to fruit. After the petals fall, small green fruits emerge, encased within the remnants of the flower structure known as the shuck. This initial fruit set determines the potential yield for the season. Growers may apply fungicides to prevent diseases like brown rot, which can threaten the newly formed fruit.
Summer Growth Stages: Pit Hardening and Final Swell
Once the initial fruit set is established, the peach follows a pattern known as the double-sigmoid growth curve, consisting of three distinct phases.
Phase 1 (S1): Cell Division
The first stage (S1) is characterized by rapid growth driven by cell division, establishing the fruit’s potential size. This phase occurs swiftly after the shuck is shed in the late spring.
Phase 2 (S2): Pit Hardening
The fruit then enters the second stage (S2), or lag phase, where external growth slows dramatically. During this time, the seed forms, and the stone surrounding it undergoes lignification, or hardening. The tree directs its energy toward strengthening the internal pit.
Phase 3 (S3): Final Swell
Finally, the peach enters the third stage (S3), the final swell. This is a period of renewed, rapid growth where cell expansion becomes the dominant process. This causes the fruit to quickly increase in volume and accumulate sugars, defining the peach’s flavor and sweetness. This final swell typically occurs in the last four weeks before harvest.
Determining Harvest Timing by Location
The timing of the peach harvest is heavily influenced by regional climate and accumulated heat, meaning the season starts and ends differently across growing regions. In the warmest southern regions, such as Florida, the harvest can begin as early as April or mid-May. Conversely, in northern states like Michigan or Idaho, the season may not begin until mid-to-late July and can extend through September or October.
A primary tool for predicting the harvest date is the use of a heat unit model, often calculated as Growing Degree Days (GDD). These models track the accumulation of heat above a base temperature, providing a reliable prediction of when a peach will reach maturity. The date of the last average frost also plays a part, as a later frost pushes the bloom and subsequent harvest back in time.
How Peach Variety Affects Season Length
The specific variety of peach planted is the genetic factor that dictates the length of the fruit development period. Peach varieties are categorized as early-season, mid-season, or late-season, based on their inherent “Days to Maturity” (DTM)—the number of days required from full bloom to harvest. Early-season varieties, like ‘Flordaking,’ have a shorter DTM and can be ready for picking in late spring or early summer. Mid-season varieties, such as ‘Redhaven,’ typically ripen during the peak summer months of July and August. Late-season varieties have the longest DTM, allowing them to hang on the tree until late August or early September, giving them more time to accumulate size and sugar. Commercial growers strategically plant a succession of these varieties to extend the availability of fresh peaches.