This expert article describes in detail all the factors that affect the cultivation of quality forest seedlings of narrow-leaved ash for artificial regeneration and afforestation. So far no attention has been paid to the quality of the seedlings given the new and completely changed adverse ecological and biological factors occurring in narrow-leaved ash stands in Croatia. The quality of field ash seedlings was determined solely by one morphological factor, which is usually the shoot height, which is not good. The paper defines the concepts of morphological and physiological quality of seedlings. Methodologies for measuring the morphological and physiological characteristics of forest seedlings and their importance for survival, growth and growth after field planting are described. Morphological features include shoot height, stem diameter, height: diameter ratio, bud length, root and stem volume, weights, shoot: root ratio, and colour, form, and damage. Physiological properties are: cold hardiness, root growth potential (RGP), bud dormancy and foliar nutrient concentration. Three stress factors that affect the decrease in forest seedling quality, survival, growth, and field gains are described, namely: plant moisture stress (PMS), temperature stress, and physical stress (falling, crushing, vibration, surface damage, and root tearing).All other stress factors that affect the decline in the quality of forest seedlings, which occurs during the period from the nursery to field planting, have been identified. The role of an individual stress factor on seedlings is clarified, and so is the cumulative influence of multiple stress factors. The article deals with the correct handling of seedlings from harvesting in the nursery to afforestation. Recent patented protection options for seedlings from the time of removal from the nursery or cold storage truck to planting in the field are presented