When growing plants—whether cannabis, vegetables, or herbs—the quality of the harvest plays a crucial role. A proven method for achieving the best results is flushing before harvest. But what exactly does it entail? Why is it so important, and how do you do it correctly? In this article, you’ll learn everything you need to know about flushing—from the definition and proper application to the scientifically proven benefits.
1. What is flushing?
Definition:
Flushing refers to the deliberate process of washing out excess nutrients from the root zone of the plant. This occurs through heavy watering in the last one to two weeks before harvest.
Purpose:
- Removal of mineral and fertilizer residues
- Improvement of aroma and taste
- Promoting clean, natural ripening
Scientific background:
Plants store nutrients in their leaves and flowers. Flushing forces them to use up their own reserves, resulting in a pure, unadulterated end product.
2. Why is flushing important before harvest?
2.1 Avoiding residues
Excess fertilizers can accumulate in plants and lead to an unpleasant, chemical taste. Flushing prevents this by removing salts and excess nutrients from the substrate.
2.2 Taste improvement
Studies (e.g., by GreenTech universities) show that flushed plants have up to 70% fewer nutrient residues. The result: a purer, more intense aroma.
2.3 Environmental friendliness
Flushing reduces the amount of chemicals entering the soil, increasing the sustainability of cultivation.
3. Is flushing necessary with 100% organic nutrients?
A common question is whether flushing is necessary even when using 100% organic nutrients. The answer depends on several factors:
3.1 Organic vs. synthetic nutrients
- Synthetic nutrients are mineral salts that accumulate quickly and often require flushing.
- Organic nutrients are slowly broken down by microorganisms, reducing the risk of surpluses.
3.2 When is flushing also useful for organic nutrients?
✅ Overfertilization: Even organic fertilizers (e.g., guano, fish meal) can leave residues if used excessively.
✅ For better flavor: A light flush can help enhance aromatic compounds (terpenes).
✅ In hydroponic systems: Organic residues can impair the root environment in coco or hydroponic systems.
3.3 When can flushing be omitted?
❌ In living soil: A healthy microbial balance regulates nutrients naturally.
❌ With sparing fertilization: When plants mature naturally and show no signs of over-fertilization.
Tip: Test a small batch with and without flushing to check the difference in taste!
4. How is flushing done correctly?
Step-by-step instructions
| Step | Description |
|---|---|
| 1. Time | Start flushing 1–2 weeks before harvest. |
| 2. Amount of water | Use 2-3 times the volume of the pot (e.g. 10 liters for a 5-liter pot). |
| 3. Control | The water running out should be clear – a sign of successful rinsing. |
| 4. Repetition | In heavily fertilized soils, a second flushing may be necessary. |
For organic growers:
- Use pH-neutral water (6.0–6.5) or mild detergents such as molasses (promotes microbes) or coconut water (contains natural enzymes).
5. Advantages of Flushing at a glance
✅ Better taste – No chemical additives
✅ Higher quality – Cleaner, more natural harvest
✅ Environmentally friendly – Reduced chemical input
✅ Cost-effective – Less fertilizer use in the final stage
6. Conclusion: Flushing is worth it – but it depends on the situation!
- For synthetic nutrients: Flushing is almost always recommended.
- Regarding organic nutrients: Depends on the cultivation method – often unnecessary with Living Soil, but still useful with strong organic fertilizers.
Try it out and decide for yourself what works best for your harvest! 🌱