This paper presents the results of beech seedling growth under the influence of suboptimal nutrition with nitrogen (N), phosphorus (P), magnesium (Mg) and iron (Fe). The aim of the paper was to bring this issue closer to forestry practice through the discussion of the obtained results in the context of current knowledge on plant growth under the influence of suboptimal nutrition with mineral nutrients. In the early spring of 2019 year, 30 beech seedlings originating from one natural mixed stand of sessile oak and common beech were transplanted into a sterile substrate (agroperlite). After transplanting, over the next three years six transplanted plants for each treatment were regularly watered (treated) with a complete nutrient solution (KO treatment), or nutrient solutions in which nitrogen (-N treatment), phosphorus (-P treatment), magnesium (-Mg treatment) or iron (-Fe treatment) was omitted. Therefore, the beginning and duration of leaf development (2020 and 2021), the number of leaves and the average and total leaf area (2019, 2020 and 2021) were recorded on six plants within each of the five previously described treatments. The root collar diameter and the height of the stem were measured in spring 2019 and autumn 2021, based on which the diameter and height increment of beech seedlings and their slenderness at the beginning and end of the experiment were calculated. In addition, on the treated saplings we determined the dry mass of leaves, stems and roots, and the total length of coarse and fine roots as well as the number of forks and tips of fine roots, which was done in autumn 2021 after their removal from agroperlite. Based on the comparison of the obtained results between the plants in the control and other treatments, it was possible to conclude the following. Under the impact of suboptimal nutrition of beech saplings with P there was a delay in spring bud burst and the beginning of leaf development. The slowest leaf development was observed under the impact of suboptimal nutrition with N and Mg. The average leaf area was not significantly affected by suboptimal nutrition with any nutrient. The decrease in the number of leaves and their total area under the impact of suboptimal nutrition with all nutrients was recorded only in the last year of the experiment. Stem diameter and height increments were also negatively affected by suboptimal nutrition with all nutrients, and reduced saplings slenderness was observed only under the impact of suboptimal Fe nutrition. The total length of coarse and fine roots was also negatively affected by suboptimal nutrition with all nutrients except N. Under the impact of suboptimal N nutrition, there was an increase in the total length of the fine roots as well as an increase in the number of forks and tips of the fine roots. Nevertheless, suboptimal nutrition with all nutrients had a negative effect on the dry mass of coarse and fine roots, including N.