Causes of Yellowing Lower Leaves During PreflowerUpdated 3 months ago
It’s not unusual to notice yellowing on the lower leaves right as cannabis plants enter pre-flower and begin their stretch. While it can look alarming, this symptom often has a straightforward explanation. The key is understanding how widespread the yellowing is and what else the plant is telling you.
Below are the most common reasons lower leaves fade during this stage—and how to respond.
1. Normal Aging and Energy Reallocation
As plants shift from vegetative growth into flowering, their priorities change. Older fan leaves—especially those low on the plant and receiving little light—may be phased out as the plant redirects energy toward new growth and future bud sites.
How to tell it’s normal:
Yellowing is limited to a few bottom leaves
Upper growth remains green and vigorous
No spotting, burning, or deformation
In this case, there’s usually nothing to fix. The plant is simply optimizing itself for flowering.
2. Early-Flower Nitrogen Shortage
Although cannabis requires less nitrogen once flowering begins, it still needs some—particularly during the stretch. If nitrogen is insufficient, the plant will pull it from older leaves, causing them to yellow and eventually drop.
Signs this may be the issue:
Yellowing progresses upward, not just at the base
Leaves fade evenly rather than spotting or crisping
Growth may slow slightly
What helps:
Use a bloom or transition nutrient that still includes a modest amount of nitrogen
Avoid switching too abruptly from veg nutrients to zero-nitrogen bloom feeds
3. Nutrient Uptake Problems (Lockout)
Sometimes nutrients are present but unavailable. This can happen when root conditions prevent proper absorption.
Common contributors include:
Incorrect pH (soil generally performs best between 6.0–7.0)
Excess salts from frequent or heavy feeding
Poor root oxygen due to overwatering
Steps to take:
Check runoff pH if you can
Review your watering schedule—roots need both moisture and air
If buildup is suspected, a light flush with properly pH’d water may help reset the medium
4. Stress at the Plant Base
Lower leaves live in a different microclimate than the canopy. During stretch, dense foliage, heat, or stagnant air near the pot can stress older leaves first.
Potential stressors include:
High temperatures near the soil surface
Low humidity
Weak airflow around the base of the plant
Improving circulation and maintaining stable environmental conditions can prevent unnecessary leaf loss.
Final Thoughts
A few yellowing leaves at the bottom during pre-flower are often nothing to worry about. Focus on:
The health of new growth
The speed and pattern of yellowing
Root zone conditions and feeding balance
If discoloration spreads quickly or reaches upper leaves, act early by checking pH, reviewing nutrients, and dialing in your environment. Catching small issues at this stage helps set the plant up for a smooth flowering cycle.