The main objective of the thesis was to assess the effect of planting term (autumn/spring) and commercial additives application (slow-release fertilizer Silvamix, hydrogel Stockosorb/Agrisorb) on Norway spruce (spruce) and European beech (beech) bareroot (BR) and containerized (CR) plantation development established on study sites in Javorie Mts. and Strážovské vrchy Mts. Experimental plot in Javorie Mts. was established in autumn 2014 and spring 2015, experimental plot in Strážovské vrchy in autumn 2018 and spring 2019. Effects of hydrogel and commercial ectomycorrhizal (ECM) additive Ectovit application on the growth and physiological parameters of spruce and beech planting material were investigated also under simulated drought conditions in forest nursery Lokca. Average survival of planted seedlings on the plot in Javorie Mts. was 51 % five years after planting and 62 % on the plot in Strážovské vrchy Mts. two years after planting. In conditions of both experimental plots, spruce survived and grew better than beech. Markedly lower survival of autumn than spring planted BR spruce was observed on both sites. Fertilizer Silvamix temporarily improved growth of BR beech in Javorie Mts. No significant effect of applied fertilizer was found on plantation development in Strážovské vrchy. Seedling root system dipping into hydrogel before planting, stimulated root system growth of BR spruce in Strážovské vrchy Mts. In conditions of planting sites hydrogel application had no significant effect on the growth of seedling aboveground part. Reduced water availability in pot experiments significantly influenced root growth of spruce and beech samplings. In conditions of simulated water shortage, hydrogel application increased ratio of vital short roots on fine roots of beech. Short root colonization of spruce and beech samplings by Ectovit included ectomycorrhizal fungi was not confirmed. Non-pronounced effect of the additives on the spruce and beech BR and CR plantation development is probably a consequence of relatively favorable conditions of study sites, as well as absence of any extreme climatic events during plantation monitoring. In pot experiments, significant effect of water availability, especially on root system dry mass of spruce and beech saplings emphasized the importance of soil water on planting material development during early growth stages.