Self-Renewal of Invasive Goldenrods (Solidago spp.) as a Result of Different Mechanical Management of Fallow

The spread of invasive plants is one of the most significant causes of biodiversity loss in natural, semi-natural, and anthropogenic habitats in Poland. This two-year study aimed to assess the rate of self-renewal of Canadian goldenrod (Solidago canadensis L.) and giant goldenrod (S. gigantea Aiton), and the possibility of achieving full generative development on fallow land restored to agricultural use with mechanical treatments. The following research objects were examined: the control (no mechanical treatments); one-time mowing; two-time mowing; one-time mowing plus one-time rotary tilling; and one-time mowing plus two-time rotary tilling. The phenological development of Solidago spp. was observed every 14 days from June to September each year. In October of each growing season, the aboveground parts of goldenrods’ biomass were measured, and selected morphological parameters were assessed. Two-time mowing and one-time mowing with two-time rotary tilling resulted in the highest reductions in the share of goldenrods in the generative stages of development, of 64.0% and 51.7% compared to the control, respectively. The two-time mowing treatment was the most effective at inhibiting goldenrods’ biomass accumulation, with a 57.7–77.0% decrease in biomass compared to the control. This treatment also reduced the number of flowering shoots and inflorescence lengths of both Solidago species.