Control
Crop Steering for Generative Growth: Substrate Control for Maximum Flowering
What Is Crop Steering?
Crop Steering is the deliberate manipulation of substrate moisture, nutrient concentration and climate parameters to guide the plant in a specific growth direction — either vegetative (leaf and shoot growth) or generative (flowering and fruit development).
The principle is based on controlled plant stress: Through targeted fluctuations in the root zone (dry-back cycles, EC increase) and in the climate (day/night temperature differential), the plant is encouraged to invest energy in reproduction rather than vegetative growth.
Generative vs. Vegetative Compared
| Parameter | Vegetative | Generative |
|---|---|---|
| Goal | Leaf growth, mass, root development | Flowering, fruit development, terpenes |
| Dry-Back | Low: 5 – 10% | High: 10 – 20% |
| First Irrigation | Early (at lights-on) | Late (2 – 4h after lights-on) |
| Last Irrigation | Late (near lights-off) | Early (2 – 3h before lights-off) |
| Input EC | Low to medium: 0.8 – 1.4 | Medium to high: 1.4 – 2.0 |
| Substrate Moisture | Kept consistently high | Deliberate fluctuations |
| Temperature DIF (Day − Night) | Small: 1 – 3 °C | Large: 5 – 10 °C |
| Irrigation Volume per Event | Smaller, more frequent | Larger, less frequent |
Dry-Back Explained
Dry-back refers to the percentage weight loss of the substrate between the last irrigation of the previous day and the first irrigation the next day. It is the central metric for crop steering.
How to Measure Dry-Back
- Substrate scales: The gold standard. They continuously measure pot weight and automatically calculate VWC and dry-back.
- VWC sensors: Capacitive or TDR sensors measure the volumetric water content directly within the substrate.
- Manual method: Weigh the pot before the last irrigation, weigh again the next morning before the first irrigation. Calculate the difference as a percentage of the saturation weight.
Dry-Back Target Values
| Steering Direction | Dry-Back (%) | Effect |
|---|---|---|
| Strongly vegetative | 2 – 5% | Maximum leaf growth, root expansion |
| Mildly vegetative | 5 – 10% | Balanced growth |
| Mildly generative | 10 – 15% | Transition to flowering, moderate stress |
| Strongly generative | 15 – 20% | Maximum flower production, terpene synthesis |
Generative Steering in Practice
- Delay the First Irrigation (P1 Event) Start the first irrigation 2-4 hours after lights-on. The substrate dries out more, which amplifies the generative stimulus. In the first few days after switching, 2 hours is sufficient — increase to 3-4 hours over 5-7 days.
- Larger Individual Doses, Fewer Events Instead of 6x 200 ml, opt for 3x 400 ml. This creates an alternation between strong saturation and subsequent drying — exactly the stress cycle that generative steering requires.
- Bring Forward the Last Irrigation Stop irrigation 2-3 hours before lights-off. The substrate dries out throughout the entire dark period. The longer the dry period, the stronger the generative stimulus.
- Increase EC Gradually raise the input EC to 1.5-2.0 mS/cm. The higher salt concentration creates osmotic stress in the root zone. Increase by no more than 0.2 mS/cm per day.
- Lower Night Temperature (DIF Strategy) Lower the night temperature to 16-18 °C with a day temperature of 24-28 °C. This temperature differential (DIF) of 5-10 °C promotes compact internodes and stronger flower development.
- Monitor Dry-Back Daily Measure the dry-back every morning before the first irrigation. Target: 10-20%. Adjust irrigation timing and volume if the value falls outside the target range.
Common Mistakes in Crop Steering
When to Steer Generative vs. Vegetative
| Cycle Week | Phase | Steering |
|---|---|---|
| Week 1 – 2 | Seedling / Clone | Strongly vegetative — high moisture, low EC, no dry-back |
| Week 3 – 5 | Vegetative | Vegetative — consistent moisture, moderate EC, 5-10% dry-back |
| Week 6 (Flip) | 12/12 Switch | Transition — gradually shift to generative over 3-5 days |
| Week 7 – 8 | Stretch / Early Flower | Mildly generative — 10-15% dry-back, EC 1.4-1.6 |
| Week 9 – 12 | Full Flower | Strongly generative — 15-20% dry-back, EC 1.6-2.0, large DIF |
| Week 13 – 14 | Late Flower / Ripening | Maintain generative, reduce EC from week 13 (flush phase) |
Frequently Asked Questions
What is the difference between generative and vegetative steering?
Vegetative steering promotes leaf growth and mass through consistent substrate moisture, early irrigation and lower EC. Generative steering promotes flowering and fruit development through stronger dry-back cycles, delayed first irrigation, higher EC and a greater day-night temperature differential.
How much dry-back is optimal for generative steering?
For generative steering, 10-20% dry-back is optimal. During the vegetative phase, only 5-10% is typical. The exact value depends on the substrate type — coco dries out faster than rockwool, and rockwool retains moisture longer. Start conservatively at 10-12% and increase gradually.
When should you switch from vegetative to generative steering?
The transition occurs when switching to the 12/12 light cycle. Do not start abruptly — gradually reduce irrigation frequency and increase EC over 3-5 days. Monitor the plant response closely during the transition phase.
Do I need special sensors for crop steering?
Substrate scales or VWC sensors are ideal but not mandatory. At a minimum, you need an EC meter and a way to estimate substrate weight (e.g., lifting the pot). Professional setups use tensiometers or capacitive soil moisture sensors. SteerMind AI can help you implement effective steering even with manual measurements.