The present study was inspired by scientific reports describing the positive effects of silicon preparations on fruit and vegetables in horticulture. The use of silicon preparations in forest protection represents a new research application, especially in the cases of oak seedlings that are damaged by oak powdery mildew. Additionally, these preparations increase the photosynthetic efficiency of the seedlings, and thus promote increased biomass and better nutritional value of the root systems. The new idea of using silicon formulations in forestry, based on the initial test results, is particularly important for seedlings in the post-planting period in forest plantations. In particular, these preparations increase yield and plant growth, and improve plant health. So far, no comparable studies have been conducted on forest tree species. To this end, one year-old pine (Pinus sylvestris L.) and two year-old English oak (Quercus robur L.) seedlings were sprayed with silicon preparations of different concentrations, and changes in growth parameters and photosynthetic efficiency were observed. The main objective of the study was to determine the effect of the silicon preparation on the seedlings during their first life span, i.e., the first year after planting. In this study, 50 pine and 50 oak seedlings were sprayed three times with the silicon preparation, in five variants (control; concentrations of 1%, 2%, 3% and 5%), as well as the chlorophyll fluorescence, height, thickness and biomass of the roots, were measured. It was found that the treatment with a concentration of 2% was better and statistically, significantly different from the other variants, e.g., in terms of increasing photosynthetic efficiency.