The autoflower plant, unlike its photoperiod counterpart, transitions to its flowering phase based on age rather than a change in the light cycle. This unique genetic trait, inherited from Cannabis ruderalis, means the plant operates on an internal biological clock. The “stretch” phenomenon is the plant’s rapid vertical growth spurt that occurs as it shifts energy from vegetative growth to flower production. This sudden increase in height is a predictable phase in the autoflower’s relatively short life cycle.
The Autoflower Timeline: Seedling to Pre-Flower
The autoflower’s journey begins with a brief seedling phase, typically lasting the first two weeks after germination. During this time, the plant focuses primarily on developing a robust root structure and establishing its first true leaves. Growth is initially slow and compact as the plant secures its foundation.
Following the seedling period, the plant enters the vegetative phase, generally spanning Weeks 3 and 4. This is when the plant accelerates its production of fan leaves and lateral branches, rapidly building the structure that will support future flower sites. Growers will notice a significant increase in overall plant mass during this time.
The transition to the reproductive stage often begins around the end of Week 4 or the start of Week 5. This shift is signaled by the appearance of pre-flowers, which are tiny white hairs, or pistils, emerging at the nodes where the branches meet the main stem. This visible sign indicates the plant is preparing to dedicate resources to bloom, setting the stage for the growth spurt.
Identifying the Stretch Phase
The rapid vertical growth known as the stretch phase generally begins around Week 4 or Week 5. This timing coincides precisely with the plant’s hormonal shift into pre-flowering and the start of the bloom cycle. The exact trigger is genetic, but this short window represents the plant’s attempt to maximize its exposure to light before it fully commits to bud development.
For most autoflower strains, this growth spurt typically lasts between 10 and 20 days before vertical growth slows significantly. During this period, the plant will rapidly elongate the space between its nodes, a process called internode stretching. This results in a noticeable increase in height, often causing the plant to double its size, though highly Sativa-dominant genetics may stretch even further.
The degree of stretching is heavily influenced by the plant’s inherited traits; Indica-leaning varieties exhibit less vertical gain than Sativa-dominant ones. Environmental factors, particularly light intensity, also play a role, as plants under insufficient light will stretch excessively to reach the source. Understanding the start of the stretch—Week 4 or 5—is important because it dictates when a grower must make canopy management decisions.
Managing Plant Needs During Rapid Growth
The onset of the stretch phase necessitates an immediate adjustment in the plant’s nutrient profile to support the sudden change in growth. While the plant is still increasing in size, it requires a shift away from high-nitrogen vegetative formulas toward a nutrient solution richer in phosphorus (P) and potassium (K). This change supports the development of flower sites and strengthens the plant’s structural integrity.
The rapid vertical growth also requires constant monitoring of the distance between the plant canopy and the light source. Plants can grow several inches in a single day during the peak of the stretch, quickly reducing the distance to the grow light and risking light burn. Growers must adjust the light fixture height daily to maintain an optimal distance and prevent the degradation of upper foliage and flower structures.
Because stems harden quickly during this phase, any low-stress training (LST) or canopy manipulation techniques should be applied early in the stretch or just before it begins. If the stretch is aggressive, the plant’s newly elongated branches may require physical support, such as staking or trellising, to prevent bending or collapsing. Providing this support stabilizes the plant, allowing it to dedicate maximum energy to the developing flower clusters.