Afforestation of marginal agricultural lands is an important issue in the land use changes running in Europe at present. The aim of the presented study is the documentation of effects of site improving material Alginite three years after afforestation of agricultural land in the locality with unfavourable hydrophysical regime. The impact was evaluated on growth parameters (height increment, mortality and foliar nutrient content) of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), Scots pine (Pinus sylvestris L.) and a mixture of English oak (Quercus robur L.), red oak (Quercus rubra L.) and Norway maple (Acer platanoides L.) seedlings on former agricultural land in central Bohemia, Czech Republic. The research plot consists of 36 square sub-plots, each sub-plot is 400 m 2 in size. Each sub-plot consists of 400 individuals, except Douglas-fir with 200 individuals. The following doses of Alginite were applied: control (variant A without Alginite), 0.5 kg of Alginite (B) and 1.5 kg of Alginite (C) on both conifers and broadleaves. The results showed that Alginite application had greater positive effect on height growth of seedlings than mortality, especially variant C. In most of the cases height increments were significantly positively affected (p < 0.05) by both variants of Alginite application only in the third year after planting. Alginite applications were also connected with differences in the foliar nutrient content, especially with higher magnesium and phosphorus values. The highest differences among Alginite variants were observed for Norway maple and English oak, while the lowest for red oak and Scots pine within all monitored parameters.