L'uso dei wildflowers nel paesaggio urbano: aspetti colturali e progettuali

The term "wildflowers" indicates spontaneous herbaceous plants with showy blooms, interesting for their ornamental value and used for the design of green areas. They are typically characterized by high rusticity and limited climatic requirements, in particular regarding the nutrient supply, irrigation, and management. Wildflowers are plants found originally in rural uncultivated areas, but also in urban environments such as cities , particularly in suburbs, characterized by poor soils, with structural and nutritional defects. These characteristics make them an interesting resource for the design in degraded areas, roundabouts, marginal areas, parking areas, roadsides, green areas in cities, or where other plants would suffer the effect of the environment or the substrate. The use of these plants is especially interesting for the preservation and increase of the biodiversity in urban environments and for the conservation of native species that are not used in traditional design. Wildflowers are usually sown in mixtures defined by the designer or readily available on the market. These mixtures, chosen to avoid allelopathy and competition, must contain a good balance between annual and perennial species. Annual plants have colored and impressive flowers, even if short-lived, while perennials provide a longer flowering. The used species are herbaceous spontaneous, mono or dicotyledons, annual or perennial, native or from other distribution areas, though not invasive. They have therefore a quick settlement and are able to cover a large area in a short time. Species belong to various families, with a prevalence of Asteraceae and Fabaceae, sometimes associated with Graminaceae, that are useful to stabilize the mixture. Since these hardy species, agronomic interventions are minimized. Besides the removal of seed dormancy, real issue of wildflowers, intervention is limited to the management of the weeds and to the periodic mowing. Irrigations and fertilizations are limited to the first few weeks after planting, because of the negative effects observed experimentally of certain nutrients such as nitrogen and phosphorus. High doses of these elements in fact involve an excessive growth of nitrophilous species. Regard the planting, it is important to perform some processing (milling and rolling) to ensure a good bed and to avoid that smaller seeds go too deep, no longer able to germinate. The seeding may be done in spring or autumn, and is carried out by different methods. The germinability essentially depends on the thermal and light conditions and is a factor still in the experimental phase, especially in the Mediterranean area, where there are less knowledge about it. In recent decades, particularly in United States and in Northern Europe, there is a growing interest in these species, especially for the recovery and renaturalization of degraded areas. In Italy, however, this method is still little known and used. It's important to explore and experience the power of native herbaceous flora, especially considering the high number of species present in the Mediterranean. The identification of native plants used as wildflowers is important and useful to enrich the offer of plants to be used in design and increase biodiversity in urban environments. This approach allows to greatly reduce the cost of installation and management, while ensuring a quick settlement and scalability of the blooms, together with a great ecological and landscape value.