The effect is mostly in the first weeks after cloning or transplanting, when roots are small and the plant is stressed. Warm, evenly damp medium and gentle light matter more than any product. Once a plant has a healthy root system, there's little reason to keep adding them.
Mycorrhizae work differently, because they live on the roots rather than boosting them. Great White goes straight onto the roots at planting: dust it on the roots or in the hole for seeds, clones and transplants, or about 1 tsp (~5 g) per 40 L in hydro. Others: DutchPro Take Root and GEN200 Grow Roots, dosed per the label.
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