Flushing (Flash) is the final preparation for harvest, aimed at removing residual nutrients and salts from the growing medium. This phase enhances the bud’s natural flavours, smoothness, and overall quality by encouraging plants to utilise their internal nutrient reserves.
| Parameter | Ideal range |
| Water pH (Soil) | 6.0–6.5 |
| Water pH (Coco Coir) | 5.7–6.2 |
| Water pH (Hydroponics) | 5.5–6.0 |
| EC Soil/Coco/Hydroponics (mS/cm) | 0.0–0.4 |
| Day Temperature (°C/°F) | 22–24°C / 72–75°F |
| Night Temperature (°C/°F) | 18–20°C / 64–68°F |
| Root Zone Temperature (°C/°F) | 18–22°C / 64–72°F |
| Leaf Surface Temperature (°C/°F) | 22–24°C / 72–75°F |
| Related Humidity (RH%) | 30–45% |
| VPD (kPa) | 0.8–1.0 |
| Optimal CO₂ (ppm) | 400–600 |
| PAR (μmol/m²/s) | 600–800 |
| Lights Hrs/Day | 12/12 (Photoperiod) or unchanged for Autoflowers |
| Light Intensity (%) | 90–100% |
| Light Distance (cm/in) | 20–40 cm / 8–16 in |
| Substrate Moisture | Lightly moist, reducing during final days |
| Primary Nutrients | n/a |
| Secondary Nutrients | n/a |
| Micronutrients | n/a |
| N-P-K | 0–0–0 |
| LST | n/a |
| HST | n/a |
| Medium | Frequency | Volume (ml/L) | Runoff % |
| Soil | Every 1–3 days | 3× pot volume | 30–45% |
| Coco Coir | Daily | 2× pot volume | 35–50% |
| Hydroponics | Continuous | Fresh water only | n/a |
Nutrients are no longer necessary during this phase. Plants will utilise stored nutrients, resulting in smoother flavours and improved burning characteristics.
| Milestones | ⬜ | Runoff EC is within the target range (0.0–0.4 mS/cm). |
| ⬜ | Natural fading of leaves (yellowing) indicates nutrient depletion. | |
| ⬜ | Trichomes have reached the desired level of maturity (cloudy/amber). | |
| Checklist | ⬜ | Flushing completed with clean, pH-balanced water. |
| ⬜ | Environmental conditions maintained at optimal levels. | |
| ⬜ | Trichomes checked and ready for harvest. |
Flushing is the process of using clean, pH-balanced water to remove residual nutrients and salts from the growing medium before harvest.
Start flushing 1–2 weeks before harvest, depending on your growing medium and nutrient schedule.
Flushing improves the flavour, aroma, and smoothness of the final product by removing excess nutrients.
Use clean, pH-balanced water such as distilled or reverse osmosis (RO) water.
Measure the EC and pH of the runoff to ensure salts and nutrients are being removed effectively.
No, as long as you avoid overwatering and maintain proper environmental conditions, flushing is safe.
Yes, autoflowers benefit from flushing just like photoperiod plants to enhance the final product's quality.
Flushing is complete when the runoff EC matches the input water’s EC (typically 0.0–0.4 mS/cm).
Flushing can still be beneficial in organic grows to remove any accumulated salts or residues from organic fertilisers.
Yes, flushing agents can help break down salt buildup, but use them sparingly and follow the manufacturer’s guidelines.
Slightly lowering light intensity can reduce stress on plants and improve trichome preservation.
No, discontinue CO₂ supplementation as it’s unnecessary in this phase and can waste resources.
