The flowering of the apricot tree, known as the bloom, represents the first visible sign of the spring growing season and the start of fruit development. This biological process is heavily dependent on specific environmental cues, making its timing highly variable from year to year and location to location. Understanding when an apricot tree will bloom involves recognizing the complex interaction between its long-term winter preparation and the immediate spring weather.
The Typical Apricot Bloom Window
Apricot trees are consistently one of the earliest fruit species to flower, often beginning their bloom in late winter or very early spring. Depending on the latitude and local microclimate, this primary flowering period generally falls between February and April. In warmer, southern regions, buds may open near the beginning of February, while in northern areas, the bloom might be delayed until late March or early April. The period of full bloom, when the majority of flowers are open, typically lasts only about one week. However, the entire flowering process can span up to three weeks.
Cultivar selection plays a significant role in determining the exact timing, as some varieties are specifically bred for early or late flowering. Late-blooming cultivars, such as ‘Chinese’ or ‘Harglow,’ are favored in regions prone to late spring cold snaps, as they naturally delay the most vulnerable phase. Apricots almost always bloom before other common stone fruits like peaches or cherries in the same location.
The Essential Winter Requirement
The foundation for spring flowering is established months earlier during the winter, through a process called dormancy. This biological prerequisite is measured in “chilling hours,” which are the cumulative hours the tree spends within a specific temperature range, typically between 32°F and 45°F (0°C and 7°C). If an apricot tree does not receive a sufficient number of chilling hours, its dormancy will not fully break, regardless of how warm the subsequent spring weather becomes.
This failure to exit dormancy correctly leads to physiological problems, manifesting as delayed, erratic, or uneven blooming. Buds may open over a prolonged period, or a significant portion may fail to open at all, resulting in a poor and scattered fruit set. Different apricot cultivars have distinct chilling requirements, which is a major factor in varietal selection.
Low-chill varieties, such as ‘Katy’ or ‘Gold Kist,’ may require only 300 to 500 chilling hours, making them suitable for mild winter climates. By contrast, high-chill cultivars like ‘Moorpark’ or ‘Harcot’ may need 600 to 900 hours or more to ensure a healthy, synchronized bloom.
Factors That Shift Bloom Timing
Once the tree’s chilling requirement has been met, the final trigger for bloom is the accumulation of warmth in late winter and early spring. The tree exits internal dormancy and enters a state called ecodormancy, where external environmental factors, particularly temperature, control the pace of development. Scientists quantify this necessary warmth using a metric known as “heat units” or Growing Degree Hours (GDH). GDH represent the sum of thermal energy accumulated above a certain base temperature, which signals to the flower buds that conditions are favorable for growth.
A sudden, prolonged warm spell in late February or early March can dramatically accelerate the accumulation of these heat units. This rapid accumulation forces the flower buds to open much earlier than the historical average, sometimes by several weeks. Conversely, a cold snap that persists after the chilling requirement is satisfied will halt the accumulation of heat units, delaying the bloom. The total heat requirement varies significantly between varieties, which is why the bloom date can fluctuate widely from year to year, even in the same location.
Protecting the Bloom
The apricot tree’s tendency to bloom early means its delicate flowers are highly vulnerable to late-season frosts, which can destroy the potential fruit crop. Apricot blossoms typically tolerate temperatures down to about 29°F (-1.7°C) when fully open. Temperatures below this threshold can cause irreversible damage to the pistil, the reproductive organ of the flower.
Growers employ several methods to mitigate the risk of frost damage, often starting with careful site selection. Planting apricot trees on slopes or slightly elevated ground helps, as cold, dense air naturally flows downward and settles in low-lying areas. Placing trees near a south-facing wall can also help by using the wall’s stored heat to raise the microclimate temperature slightly overnight.
For active protection, water is often used in the form of overhead micro-sprinklers. As the water freezes on the buds and blossoms, it releases latent heat, which keeps the temperature of the ice-encased flower very near the freezing point of water, 32°F (0°C). This thin layer of ice insulates the delicate tissue from the colder ambient air, protecting it until the sun rises. Other techniques involve using large fans or wind machines to mix the cold air near the ground with warmer air layers higher up, a practice known as breaking the temperature inversion.