The RGC Method – An Effective Tool for Detecting Root Damage in Forest Seedlings

The RGC method (Root Growth Capacity) is a standardized and practical approach for evaluating the physiological condition of root systems in container-grown forest seedlings before they are planted in the field. Root damage is a widespread but often underestimated problem in forest regeneration, particularly in northern regions where seedlings are exposed to low temperatures during cultivation, storage, and handling. Damage to roots can result from freezing, oxygen deficiency in waterlogged substrates, high salt concentrations, or insufficient root hardiness prior to frozen or outdoor storage. Because such injuries are usually not visible externally, damaged seedlings may be planted unknowingly, leading to poor establishment, reduced growth, or mortality after planting.

The RGC method was originally developed in the western United States and later adapted for container-grown seedlings in Scandinavia. Its central principle is that healthy root systems will rapidly produce new roots when placed under favorable growing conditions, whereas damaged or dead root systems will show little or no new root growth. By measuring this response, the method provides an objective indicator of root vitality rather than relying on visual inspection alone.

In practice, seedlings are placed in specially designed trays filled with a water-saturated mixture of peat and sand and cultivated in a temperature-controlled water bath for approximately three weeks. Light, temperature, and watering are carefully regulated to ensure optimal conditions for root growth while minimizing variation between samples. No nutrients are supplied during the cultivation period, as this could mask differences in root vitality. After cultivation, the substrate is removed and newly formed roots are carefully cleaned and separated from the original root plug. Root growth is then quantified either as total root length or as dry weight after drying.