The mixed deciduous forest, characterized by a continental climate, is organized in vegetation belts arranged on different altitudinal planes, each represented by dominant plant species. The Botanical Garden hosts the main deciduous species of the Italian woods, with arboreal and shrubby elements mainly of the native flora of Lazio, organized according to an aesthetic criterion.

Among the woody and shrubby species of the native flora of the Viterbo area, there are Quercus pubescens Willd. (downy oak), Quercus cerris L. (Turkey oak or Austrian oak), Quercus robur L. (common oak, pedunculate oak, European oak or English oak), Acer monspessulanum L. (Montpellier maple), Cornus mas L. (dogwood), Corylus avellana L. (hazel), Ruscus aculeatus L. ( butcher’s broom).

The herbaceous layer is under construction, currently there are specimens of Pulmonaria officinalis L., Primula elatior (L.) Hil, Cyclamen hederifolium Aiton (cyclamen) and Helleborus viridis L. (green hellebore).