Horsetail (Equisetum arvense L.) is a perennial herb which creates during the life cycle spring and summer stems. The selected species and populations were monitored in the years 2009-2011 in three different natural locations in Laborecká vrchovina (Slovakia). Samples were collected by destructive methods in all three locations. Silicon content was determined in dry biomass by AAS. Silicon content in plants ranged from 21.11 ± 3.24 g·kg^-1 to 32.80 ± 8.03 g·kg^-1. The highest content of silicon exhibited samples of the September collection. We found that the location and the year in terms of silicon content were not statistically significant. The main sources for statistical variability in the accumulation of silicon were during the collections.