The main differences are the composition of the topsoil materials and the planting.

For a gravel garden, a separating layer is deliberately installed between the natural soil and the gravel. Foil, fleece, or even concrete are used to prevent the growth of weeds. In contrast, mineral mulch merely forms a protective layer over the natural soil and ensures good aeration, slow seepage of rainwater, and protection against evaporation.

A glance at the plants reveals whether it is a drought-resistant bed or a gravel garden. Heat- and drought-resistant perennial beds are characterized by a variety of plant species. They often feature different flowering plants and grasses that provide insects with a source of food or nesting aid. Gravel gardens usually only contain individual plants of no ecological value, and the stones serve mainly as a design element.

The impression of a gravel bed may arise in the initial phase. If a perennial bed is newly planted with mineral mulch and the young plants have not yet grown luxuriantly, it may appear to be a gravel bed. The number of perennials planted alone suggests that it is a young perennial bed. Beds that are planted in shady locations also need a longer period of time before the mineral mulch is overgrown by the plants. When planting with mineral mulch, the focus is on the planting itself and the goal is to cover the entire area with greenery.

The trend toward ecologically worthless gravel gardens arose because they initially appear to be quite easy to maintain.

A gravel garden is characterized by a large area of stone, a separating layer between the gravel and the natural soil, and individual plants, most of which are ecologically worthless. The sparsely planted layer of stone heats up, stores the heat, and releases it into the environment throughout the night. During the hot summer months, this effect creates veritable heat islands.

The separating layer between the gravel and the natural soil is made of foil, fleece, or concrete. It prevents the soil from performing its functions, such as water storage, water filtration, nutrient storage, and providing a basis for plant and animal life. Incidentally, the effect of the "low-maintenance" garden is negated at the latest when, after some time, organic matter is deposited anyway, blown in by the wind or brought in by falling leaves or animals. Another problem arises when the separating layer is a sealed concrete surface. Precipitation runs directly off the surface into the sewer system, preventing water from seeping away, being available to plants, or seeping into the groundwater. Climate change will lead to more frequent heavy rainfall events, which will be less buffered and lead to overloading of the sewer system.

Low-quality, ecologically worthless vegetation threatens the habitat of insects. They cannot find food sources or nesting sites for laying eggs on these areas. The cooling effect provided by plant evaporation is also lost. Therefore, "gravel gardens" are ecological deserts and harmful to the microclimate.

The properties of mineral mulch are evaporation and frost protection for the soil, allowing precipitation to seep in slowly, protecting plants from waterlogging, and ensuring good aeration. It can be seen as a kind of start aid for plants adapted to heat and drought. On nutrient-rich soils, they quickly compete with lush, fast-growing plants, which crowd them out. Mineral mulch, as a permeable and nutrient-poor cover, is suitable for these perennials. These heat- and drought-adapted plants are important food sources for the insect world. Diverse planting offers them a wide range of food.

Compared to organic mulch materials, such as bark mulch, mineral mulch has the advantage that it reduces soil compaction caused by foot traffic, does not rot, does not leach nutrients from the soil, and does not acidify it. Once the plants have grown in, the mineral mulch layer is barely visible in its final state.

(1) Areas of developed land that are not covered by above-ground buildings, as well as open spaces beneath developed land that are covered by underground structures (e.g., underground parking garages), must be completely greened, unless they are required for a permitted use.

(3) Areas are considered green if they are unsealed and planted with trees, shrubs, perennials, lawns, and meadows, for example. Fillings made of gravel, crushed stone, and similar materials, lawn grid stones, and gravel lawns, as well as flat coverings with fleece, foils, textile fabrics, and similar materials, are not considered greening within the meaning of these statutes.