On the Frankfurt bridges there are also therapy gardens for people with disabilities, trauma patients or even people with dementia

At the entrance there is usually a meeting point

Meeting places are partly covered and invite you to rest on the seatings. Tables serve for picnics, and fruits or herbs from the therapy garden can be washed in a drinking fountain.

Seeing: Beds as a pleasure for the eyes

Particularly magnificent plants in one part of the therapy garden present visitors with a visually beautiful area throughout the year that triggers positive emotions. To get along without alternating planting, gardeners need a good aspect calendar here.

A culinary experience: Tasting

Edible plants of all kinds can be tended, harvested and then prepared here by visitors all year round. The raised beds ensure that people in wheelchairs can also access the beds at a comfortable working height.

Smell: a gateway to memories

Smells can sometimes remind us very directly of places or experiences from long ago. Accordingly, in addition to lavender, sage and many other fragrant plants, therapy gardens also contain flowers and herbs that are hardly cultivated today, anymore, such as Hyssopus officinalis, fragrant columbine or santolina.

Relaxed close your eyes and just listen

When exhaustion from the multitude of sensory impressions takes over, you can retreat to the protected "listening" area and close your eyes: The splashing of a fountain or the rustling of quaking grass create a beautiful atmosphere, as does birdsong: Dense diverse berry hedges at the edge of the area attract a particularly large number of birds here.

Experience through touching

In therapy gardens there are also people whose eyesight is not or no longer so good. For them, in addition to smelling and hearing, there is also the "feel" area to perceive plants directly:

Through various elements such as fog plants, tall soft grasses, or willow catkins, the sense of touch is particularly addressed in this area.

The bridges - a single rooftop garden: But how do you create functioning beds there?

The principle of bridge planting is similar to that of a green roof: The plants grow in a substrate layer 15 to 100 cm high, depending on the planting.

The biggest challenge on bridges: Providing the plants with everything they need without making the load too heavy

While with conventional soil it is not possible to determine exactly how much water it can ultimately store, special roof garden substrates have a specific water storage capacity.

Once the maximum possible storage amount of water is reached, the further water runs into the irrigation and drainage system below.  This prevents the planting soil from becoming too heavy for the bridge due to too much water; and on the other hand, it ensures that the plants do not stand in water and rot.

The New York Highline is still watered by hand

On the Frankfurt Bridges, though, the plants receive the water they need in dry periods not through drip irrigation, but by means of "subsurface irrigation" - unlike conventional green roof systems,

 Under the substrate layer is a water-bearing layer that provides irrigation and drainage of the beds. Capillary forces cause the water in the substrate to rise from there.

Something more effective is planned for the Frankfurt bridges

Since the plants are supplied with water from below, less irrigation water evaporates on the surface. The system can also be designed with a minimum of plastic and thus durable.

Compared to drip irrigation on the surface, it is less susceptible to external influences such as vandalism or weathering.

Drip irrigation is only used in a few places such as slopes.

A sophisticated irrigation system is planned

Underground irrigation saves water and is low on plastics.

 The principle works similarly to innovative building greening:

Water washes around small columns that support the substrate above.

The columns are slotted, allowing water to enter the columns, where it is drawn upward toward the substrate by a capillary-ready packing.

How is the water-bearing layer held?

The load-bearing elements of the retention layer are columns made of carbon concrete, a composite material consisting of two components:  concrete and carbon fibers as reinforcement.

Carbon concrete is significantly more expensive than reinforced concrete; but it is also four times lighter and five to six times stronger.

It also has a higher tensile strength, which means that less material has to be used to achieve the same effect - thus saving resources. In addition, carbon concrete has a significantly longer service life, as it is more resistant to corrosion than conventional reinforced concrete.

Carbon concrete can even be broken down into its components again during recycling: But while one has many further uses for the component concrete, there is currently little research result on the use of recycled carbon fibers.

Self-regulating capillary forces bring the water from "below ground" to the top of the plant roots!