The natural conditions for the state of flora and vegetation in a Central European landscape are altitude, climate and soils. In the Wiesbaden district, the altitudes range from 83 m above sea level on the banks of the Rhine near Schierstein to 614 m above sea level on the Hohe Wurzel in the Hochtaunus. The climate ranges from a mild winter climate with a sub-Mediterranean tendency to a cool, humid climate in the high altitudes of the Taunus. In terms of natural environment, the various parts of the urban area range from the Rhine-Main lowlands and the Ingelheim Rheinaue to the Maintaunus foreland and the Rheingau as well as the pre-Taunus to the Hochtaunus. The soils range from nutrient-rich raw loess soils and weathered soils of tertiary limestone in the lowlands and lower slopes to extremely nutrient-poor soils over Taunus quartzite and clay slate in the higher elevations.

These different conditions result in very different forms of vegetation and a very rich flora. The potential natural vegetation ranges from alluvial forests along the rivers to oak-hornbeam forests in the limestone areas and the lower Taunus slopes to the beech forests of the higher altitudes. The cultivated land created by clearing in prehistoric times was associated with a considerable enrichment of the flora, as plants accompanying cereal and wine growing immigrated. Even today, traffic routes and riverbanks are still zones along which plant species migrate. However, only the smallest remnants of natural and near-natural vegetation remain.

Residential and industrial settlements, the construction and expansion of transportation routes, the extraction of mineral resources and, above all, the intensification of agriculture have drastically changed the species spectrum of Wiesbaden's flora. This applies above all to the areas to the south and east of the more densely populated urban area. In the course of the 19th century, riparian forests and river valley meadows were destroyed on a large scale due to the expansion of the Rhine and Main rivers into shipping routes. On the lower Taunus slopes, oak-hornbeam forests were replaced by beech plantations and the establishment of spruce forests. The change in the tree population also fundamentally altered the ground flora of the forests, which have largely disappeared again today due to the expansion of urban development on the Taunus slopes. Lime mining in the Biebrich, Amöneburg and Erbenheim areas caused the complete disappearance of near-surface lime deposits and with them the specialized plant species.

The collections of the natural history department of the State Museum with the herbaria kept there document the state of the flora around the middle of the 19th century and at the turn of the 19th and 20th centuries. The list of endangered species and extinct plants is long. The forests show considerable differences between the alluvial forests on the Main and Rhine and those on the Taunus ridge. Remnants of the riparian forests can still be found here and there along the banks of the river, including numerous willow species and the now rare black poplar. This type of forest is often flooded several times a year. It is best preserved in the "Wallufer Bucht" nature reserve (NSG). On the Rettbergsaue, which is also a nature reserve, attempts are being made to reconstruct a hardwood alluvial forest through maintenance measures. This type of forest is only flooded at high water levels. The ground flora of both types of forest is very endangered, as the heavy washing in of nitrogen compounds has led to the ground flora being dominated by stinging nettles and balsam, which immigrated from the Himalayas in the 20th century and is spreading rapidly. Wild garlic used to grow extensively in the hardwood alluvial forest, but its distribution has declined sharply for the reasons mentioned above.

In the hillside forests, originally pure deciduous forests, Scots pine and European larch have also been found since the 18th century, to which spruce (Picea abies) was added in the 19th century. The forest near the city consists mainly of the so-called woodruff-beech forest (Galio odorati-Fagenion), in which remnants of the once richer stands of sessile oak and hornbeam can still be found. It is characterized by the presence of woodruff, wood fescue, nestwort, bulbous toothwort, hare's-tail, uniflorous pearl-grass, mountain golden nettle (Lamiastrum montanum), fluttering grass, witchweed (Circaea lutetiana) and some fern species. This forest zone in Wiesbaden is the main distribution area for Forster's woodrush (Luzula forsteri) in Hesse and Germany, and the city has an important role to play in protecting and preserving it. Above 400 m above sea level, the Taunus quartzite rises to the surface and forms nutrient-poor, mostly shallow soils on which the Hainsimsen beech forest (Luzula fagenion) grows. This type of forest is considerably poorer in plant species. It is characterized by the occurrence of white woodrush, wire sedge, soft meadow-grass and forest riding-grass.

Open parts of the landscape are almost entirely the result of human settlement; only where there are rocks, as in Frauenstein and Sonnenberg, can natural forest-free sites and special plant species be expected. The bank zones of the as yet unregulated rivers were also, at least in part, without trees. Open cultivated land has no natural vegetation. Agricultural land, including wooded meadows, was created by human activity. Open floodplains are only still present in the forest meadow valleys of Rabengrund, Goldsteintal and the upper Theißtal. Where wider streams flow, they are accompanied by a fringe of willows and black alders; smaller streams are lined with common loosestrife and purple loosestrife. Pennywort and stream speedwell are often found at the edge of these watercourses.

Overall, the flora of the forest meadow valleys is particularly rich. Rabengrund and Goldsteintal are typical examples and play an important role in the conservation of the local flora. Their wealth of rare species, including orchids, requires strict protection and costly maintenance measures. They preserve the landscape type of hay meadows because they have not been fertilized or used herbicides for decades due to their importance in maintaining the quality of drinking water, and the sowing of fast-growing forage grasses has not taken place. The old cereal and root crop companions that were to be found from the Neolithic period until the middle of the 20th century have largely disappeared from the modern agricultural landscape. Cornflower and poppy species as well as corncock have either disappeared completely from the fields or have moved to roadsides. The disappearance of the rarer and sometimes inconspicuous species often took place earlier and inconspicuously. The same applies to forage meadows, which are made as productive as possible through fertilization. The formerly distinct types of meadows, which were characterized by their dominant grass species, have disappeared from the agricultural landscape. Vineyards and orchards, which still exist in the districts on the western edge of Wiesbaden (Frauenstein, Dotzheim, Schierstein and Kostheim), have also lost typical species due to mechanical cultivation.

Of course, new species are also constantly immigrating, but the number of disappearing species considerably outweighs the number of new arrivals. Newcomers to the flora are often ecologically harmless and colonize free ecological niches. However, new species can also displace native species, e.g. the originally North American black-fruited two-tooth has increasingly replaced the native three-part two-tooth on riverbanks since around 1945. Angelica archangelica migrated to the banks of the rivers Main and Rhine after 1930. The South African narrow-leaved ragwort (Senecio inaequidens) is also spreading rapidly along roads and railroad lines.