The biostimulant segment is becoming increasingly important worldwide. One of the reasons for this is that fewer plant protection products are placed on the market in the European Union, and environmental sustainability also plays an important role in their use. Biostimulants are often used in several horticultural sectors, including ornamentals, to strengthen plants, achieve commercial standards, produce quality goods, increase plant vitality, and aid harvesting. This paper presents the latest results of the use of biostimulants in horticulture, with special emphasis on ornamental plant production. The legal regulation of biostimulants and their regulatory mechanisms are described in detail in the review. The main groups of biostimulants are also discussed. The response of plants to abiotic stress, in particular physiological, anatomical, and genetic changes, with regard to the application of biostimulants is also detailed. Focus is given to the areas of ornamental crop production, such as sexual and asexual propagation, cultivation, and harvesting, where biostimulants are used.

Global warming has led to irregular precipitation patterns and various abiotic and biotic stresses, resulting in unforeseen consequences for wildlife. Plant species are particularly vulnerable to these global climate changes, struggling to adapt to the increasing stressors. Urban environments exacerbate these challenges, further hindering plant survival and growth. The declining number of climate- and urban-tolerant plant species is a direct consequence of escalating stresses. However, resistance breeding approaches coupled with environmentally friendly technologies like biostimulants offer hope by expanding the pool of adaptable species. Urban vegetation plays a vital role in mitigating the urban heat island effect, supporting mental well-being among residents, and preserving biodiversity. In this study, we comprehensively review recent research findings on these topics with a focus on publications from the past 5 years. Emphasizing stress-tolerant ornamental urban plants including trees and herbaceous species becomes crucial for establishing sustainable living practices. By incorporating resilient plant varieties into urban landscapes, we can enhance ecological balance while improving the overall quality of urban environments for both human inhabitants and wildlife populations.

Soil alkalinization and salinization have increased worldwide due to extreme and/or prolonged drought periods as well as insufficient irrigation. Since crops generally react to soil salinity and high pH with decreased yield, the cultivation of tolerant biomass plants represents a reasonable alternative. Thus, we aimed to characterize the tolerance of the biomass plant Arundo donax to alkaline salt stress, induced by irrigation water containing NaHCO₃ and Na₂CO₃ mixture (1:1) at 80 mM and 200 mM of final concentration and pH 10. In terms of physiological parameters such as transpiration, chlorophyll content, photosystem II quantum efficiency, relative water content, and water saturation, the plants were resistant to the stress treatment. The negative impact on the water regime was only measured at 200 mM salt. The K/Na ratio decreased in parallel with Na accumulation. Plants also accumulated Zn, whereas a decrease in the concentration of most other elements (Ca, Cu, K, Mg, Ni, S, Si, and Sr) was detected. Antioxidative defence directed by multiple symplastic enzymes contributed to the high physiological tolerance to the applied stress. In conclusion, the cultivation of Arundo donax as a biomass crop appears to be a feasible alternative in areas affected by salinity or alkaline salt accumulation.

Urban green areas serve both the mental and physical health of the people living in the settlements; therefore, the ornamental plants used on green areas currently have a prominent role in reducing the effects of climate change and urbanization, as well as in providing ecosystem services. This is a dynamically changing, new field that requires close cooperation with several scientific fields, such as landscape architecture and plant physiology, genetics, plant breeding, and ecology. The monitoring and research of settlement communities as ecological systems greatly serves the perception of the effects of climate change and helps to mitigate them. The sustainability and economic operation of established urban green space systems can be made effective by applying innovative technologies. The Special Issue “Ornamental Plants and Urban Gardening” was launched in 2022 and published 13 articles on the topic until 31 July 2023. The published articles also have a very wide spectrum of topics, which also shows the diversity and the interdisciplinary nature of the scientific field. In the following, we present the main topics of the published articles and the results with which their authors contributed to the enrichment of the scientific field. We present a brief summary of the articles in shorter subsections.

Plant growth-promoting bacteria (PGPB) and other living organisms can help with the challenges of modern agriculture. PGPB offer ever-expanding possibilities for science and commerce, and the scientific results have been very advanced in recent years. In our current work, we collected the scientific results of recent years and the opinions of experts on the subject. Opinions and results on soil–plant relations, as well as the importance of PGPB and the latest related experiences, are important topics of our review work, which highlights the scientific results of the last 3–4 years. Overall, it can be concluded from all these observations that the bacteria that promote plant development are becoming more and more important in agriculture almost all over the world, thus, promoting more sustainable and environmentally conscious agricultural production and avoiding the use of artificial fertilizers and chemicals. Since many mechanisms of action, namely biochemical and operational processes, are still under investigation, a new emerging scientific direction is expected in the coming years with regard to PGPB, microbial, and other plant growth-stimulating substances, in which omics and microbial modulation also play a leading role.

Glyphosate is still the subject of much debate, as several studies report its effects on the environment. Sunflower (GK Milia CL) was set up as an experimental plant and treated with glyphosate concentrations of 500 ppm and 1000 ppm in two treatments. Glyphosate was found to be absorbed from the soil into the plant organism through the roots, which was also detectable in the leaf and root. Glyphosate was also significantly detected in the plant 5 weeks after treatment and in plants that did not receive glyphosate treatment directly, so it could be taken up through the soil. Based on the morphological results, treatment with higher concentrations (1000 ppm) of glyphosate increased the dried mass and resulted in shorter, thicker roots. Histological results also showed that basal and transporter tissue distortions were observed in the glyphosate-treated plants compared to the control group. Cells were distorted with increasing concentration, vacuoles formed, and the cell wall was weakened in both the leaf-treated and inter-row-treated groups. In the future, it will be worth exploring alternative agricultural technologies that can reduce the risk of glyphosate while increasing economic outcomes. This may make the use of glyphosate more environmentally conscious.