SOP: Veg to flower transition

Purpose

This SOP outlines the correct process for transitioning cannabis plants from vegetative growth into early flower. The goal is to reduce transition stress, maintain crop control, and support healthy stretch, structure, and yield development during the first 7-10 days after flip.

Scope

This SOP applies to indoor cannabis crops during the transition from vegetative growth to flower, especially from flip day through the first 7-10 days of flower initiation.

Core principle

The veg to flower transition should be managed as a controlled ramp, not a hard switch. During the first 7-10 days after flip, growers should avoid changing light intensity, irrigation strategy, dryback pressure, and environmental demand too aggressively or all at once.

Responsibilities

Grower/operator

The grower or operator is responsible for carrying out daily checks, recording plant response, measuring runoff pH and EC, tracking irrigation timing and dryback behaviour, and making gradual adjustments according to this SOP.

Head grower/cultivation lead

The cultivation lead is responsible for reviewing trend data, approving larger changes to light intensity, irrigation strategy, or nutrient strength, and confirming that the crop is transitioning cleanly into flower.

Definitions

Flip

The point at which the crop is moved from vegetative photoperiod to flowering photoperiod.

PPFD

Photosynthetic photon flux density measured at the canopy level.

DLI

Daily light integral, representing the total amount of light delivered to the crop across the photoperiod.

Dryback

The reduction in substrate water content between irrigation events.

Generative dryback

A more aggressive dryback is used to steer the crop toward reproductive growth, only once the crop is ready for it.

Runoff feedback

Daily measurement of runoff pH and EC compared against the input solution.

VPD

Vapour pressure deficit, used to assess atmospheric demand on the crop.

Equipment and measurements required

The following tools or measurements are required:

• PPFD meter or a reliable canopy light measurement method

• Irrigation and substrate monitoring tools

• Runoff collection method

• EC meter

• pH meter

• Room temperature and humidity monitoring

• Canopy temperature measurement

• Airflow assessment across the room

• Daily crop log

Pre-flip checks

Before flip, confirm the following:

• Irrigation timing is stable

• Plants are healthy and actively transpiring

• No major nutrient stress is already present

• Runoff pH and EC trends from late veg are known

• Canopy is even enough for useful PPFD readings

• Room temperature and RH are stable at lights on and lights off

• Airflow is consistent across the room

• Baseline PPFD and DLI are known at the canopy level

Do not flip a crop that is already unstable. Existing instability is often amplified during transition.

Procedure

Step 1. Ramp light gradually

At flip, change the photoperiod to flower timing, but do not immediately apply a large increase in light intensity unless there is a measured reason to do so.

Increase PPFD gradually over the first 7-10 days. Measure PPFD and DLI at canopy level rather than relying only on fixture output percentage. Watch canopy response closely each day, including leaf angle, top-leaf posture, bleaching, and tip stress.

If the crop appears comfortable and irrigation remains stable, continue the ramp. If the crop shows signs of stress, slow the increase and reassess.

Step 2. Ease into generative drybacks

During the first 7-10 days after flip, avoid aggressive drybacks. Do not use extreme steering pressure too early.

Keep irrigation timing consistent and allow drybacks to become more generative gradually as the plant adapts to new demand. Avoid large swings between overly wet and overly dry substrate conditions.

If the crop is stable and runoff trends remain acceptable, dryback pressure can be tightened gradually. If runoff EC rises too quickly or the crop shows stress, reduce steering pressure and re-stabilise.

Step 3. Track runoff feedback daily

Measure input EC and pH daily, then compare them against runoff EC and pH. Review trend direction over time rather than reacting to one isolated reading.

A controlled EC rise in early flower can be normal. However, if runoff EC continues climbing while plant stress is increasing, the transition is likely too aggressive.

If EC continues to rise and the crop is showing stress, slow the stack by increasing runoff, reducing feed strength if needed, or easing dryback pressure. If runoff trends remain controlled and the crop looks healthy, continue tightening gradually.

Step 4. Stabilise the environment through the flip

Keep VPD stable throughout the transition. Avoid large temperature or RH swings, particularly at lights on. Measure canopy temperature, not just room temperature, and confirm that airflow is even across the room.

As PPFD increases, adjust temperature and RH as needed to keep plant demand within a stable range. Do not push light harder if the environment is unstable.

Common mistakes

Common mistakes during the veg to flower transition include:

• Increasing PPFD too quickly

• Treating flip day like a full system reset

• Applying aggressive drybacks too early

• Changing irrigation frequency without tracking runoff pH and EC

• Estimating light levels instead of measuring at canopy level

• Allowing temperature or RH swings during lights on

• Ignoring canopy temperature or uneven airflow

• Reacting to single readings instead of reviewing trends

Daily monitoring checklist

During the first 7-10 days after flip, record the following each day:

• Photoperiod

• PPFD at canopy

• DLI

• Room temperature

• Canopy temperature

• RH

• VPD

• Irrigation timing

• Dryback behaviour

• Input EC

• Input pH

• Runoff EC

• Runoff pH

• Crop posture and visible stress signals

• Notes on stretch and development

Decision guide

If plants look healthy, runoff trends are controlled, and the environment is stable, continue the gradual PPFD ramp and increase steering pressure slowly.

If runoff EC rises too quickly and the crop shows stress, reduce transition pressure by easing dryback, increasing runoff, or reviewing feed strength.

If tops show stress after a light increase, pause the PPFD ramp and reassess canopy measurements, irrigation timing, leaf temperature, and VPD.

If temperature or RH swings are present at lights on, stabilise the environment before pushing the crop further.

Summary

The first 7-10 days after flip have a major influence on stretch, crop structure, and early flower performance. A clean transition depends on doing things in the right order: ramp light gradually, ease into generative drybacks, track runoff pH and EC daily, and keep VPD stable throughout the transition.

Flip week is a ramp, not a switch.