Green Facades

Without any doubt, gardening applied to vertical landscaping is one of the lines of evolution of the so-called NBS (nature-based solutions), which are clearly expanding and represent a very useful tool for the renaturalisation and future adaptation of the urban environment to climate change, which counteracts the inherent limitation of access to horizontal ground.

This application has also been boosted by the attractive aesthetic impact of today’s vertical gardens of the “vegetated wall” type (more or less modified heirs of the végétaux walls of
of Patrick Blanc). In this article we deal with the maintenance of vertical gardening and the urban application of vertical gardening in Barcelona as a case study.

istorically, the commercialisation of the vegetated wall started in our country with an often irresponsible sales policy that defined them at the time as “low maintenance” structures. Years later, this myth has fallen, and it is definitive and understood that vertical gardening requires maintenance like any other gardening installation.
We have to consider vertical gardens as sensitive installations which, due to their location, are often exposed to high evapotranspiration with a limited availability of growing medium.
. We add here a characteristic of vegetated walls: the concept of “density/resilience”.
It consists of a very high plant density associated with a very limited availability of substrate. The reduction of the volume/availability of the growing medium is an essential condition for the reduction of the total weight of the system and necessarily leads to physical and chemical limitations.

Adding these characteristics together, we could define vertical gardens, and especially “green walls”, as low-resilience structures that can be particularly susceptible to water and/or nutritional deficiencies. Their implementation, moreover, is usually associated with high costs and, therefore, the dynamics of maintenance must be very well defined from the outset to avoid failures with high economic repercussions.
For this reason, from a city perspective, it is often advisable to combine the use of green walls with other more traditional application techniques that, by combining climbing plants and suspended containers, reduce costs and simplify management.

These are mainly:

The limitation of water availability (depth of field which has to be counteracted by correct irrigation management);

The limitation of the available nutrient; The mechanical anchoring of the plants and shallow roots and, depending on the cultivation system, confined to the extent of the modulation.

As far as planting density is concerned, and in comparison with traditional gardening, we find that planting frames will strangely enough fall below 36 units/m². A frame of approximately 49 units/m² is usual, whereas in traditional gardening, planting frames of more than 25 units/m² are not usual in plantations of annual species, such as seasonal flowers, etc.

These qualities must be understood when we want to incorporate the implementation of vertical gardens on the scale of urban infrastructure and achieve the viability of their maintenance, ensuring dynamics that allow the incorporation of these tasks into municipal services. These departments have their own peculiarities and in order to successfully incorporate innovations in vertical gardens it will be necessary to be very careful in the following aspects:

Safety and ease of access to the place of work. This aspect has to be included in the project in an essential way, adapted to the possibilities of the vertical garden site, and also adapted to the means of the service that will assume the tasks of future maintenance.

In urban management, fixed access installations associated with the vertical garden (structural passeres type) are very practical and reduce subsequent costs. In the case of locations where this is not feasible, it is necessary to assess the means of elevation available to the municipal service and to foresee the possibility of arrival and location in the case of medium-sized MEWPs (mobile elevating platforms for personnel).

Other, more technical access routes (e.g. vertical work or access in specific, non-self-transporting MEWPs) must be considered more carefully than in the private sector.

Careful (and very dimensioned) application of its technification.

The technification of the installation is the great tool that allows us to counteract the characteristics of low resilience inherent to vertical gardening and at the same time allows us to optimise the time of dedication without losing security of success in the development of the garden. However, technification is also one of the most difficult tools to implement in municipal garden maintenance services.

For this reason, its sizing and monitoring forecasts are once again key in the project phase.

In terms of irrigation, the simplicity of the sensors used and the correct centralised and remotely managed management should, in the not too distant future, be the tool that will enable the following to be achieved

a simple, schematic, vertical municipal management of renaturation. The line of alarms associated with ultra-low volume flowmeters are currently proving to be much more practical than those associated with sensors that tend to require specific calibrations and maintenance.
The other major technological aspect of vertical gardening is the application of nutrients in conventional, fertirrigation or even hydroponic growing media.
Without any doubt, in urban management, simplicity is once again the key to success, and the criterion of cultivation on conventional substrates must be prioritised over hydroponic crops. Attention, however, must be paid to its application in relation to access, since the physical evolution of the conventional substrate (compaction, washing of ends, etc.) will require the cyclical contribution and revision of soil. In those installations that are difficult to access, high in height, or where lightness is a must, hydroponic/fertigation options may be the most suitable.

Enhancing resilience by botanical selection.

There are two very useful aspects here: the use of C4 and CAM species will improve our adaptation and durability in times of possible irrigation shortages. Secondly, it is highly advisable in the design of vegetated walls to incorporate species that are easy to tear out, allowing them to be replaced during ordinary maintenance visits.

Focusing now on the application of vertical gardening on a municipal scale in Barcelona, we define here three axes that overlap in evolution and importance:
1- The combination of different vertical gardening techniques: a combination of green walls and/or technical solutions with special attention to the traditional use of climbers and horizontal planting (either on the ground or in more or less technical containers).

large-format actions with urban landscape repercussions that avoid the use of végétaux walls are proposed; this line achieves an urban infrastructure of vertical landscaping with a broad scope for incorporating biodiversity (birdlife, etc.) and incorporates a combination of uses (photovoltaic, etc.). The main objective of incorporating costs and maintenance dynamics that can be assumed and are sustainable over time is achieved.

This line of work, however, does not rule out the application of new vertical gardening techniques that are evolving in the green wall market and a comparison is made of different construction techniques applied over time. In this line we could find different applications of conventional substrate gabions (works such as the Sarajevo bridge, the carriage houses of the Statute avenue) and different confined applications of technified substrates (Padrón square or Children’s Rights square).
In keeping with this line of evolution, hydroponic applications have been carried out both on climbing walls (Cerro de la Peira sports centre) and on green walls (Lope de Vega garden). In this line, the lack of textile-based gardens with municipalised maintenance, as used in other places, stands out in Barcelona. It is fair to say that the costs and dynamics of maintenance typical of the first generation of Patrick Blanc justify the reason for this lack, although the different evolutions of the textile-based construction technique currently place us in another scenario.
In a second phase of the plan for party walls, large containers were consolidated, as in the case of the Sol garden (Plaça Tísner/*BTV), gabion applications (Plaça de les Femmes del 36) and combinations of climbing plants on supports (Carrer Aragón, Rambla Badal, Vilamarí, etc.).

2- The application of botanical knowledge and careful selection of species with more and more experience for vertical use. Some of the aforementioned strategies have already been applied in the Plaça de les Dames del 36 or the Besòs dairy, as an example of the use of CAM plants, and in Joan Oliver CC in the strategy of easy ripping. 3- The application and evolution of the technique itself, associated with compensating for the risks of low resilience, such as remote irrigation management alarms. This last point is currently one of the evolutionary paths under review. It has already been used successfully in those installations where the vertical garden supply is independent (among others the Tarradellas garden or the Lope de Vega square), but its application is more difficult to apply in those irrigation systems that are shared within larger installations. In general, in municipal management it is essential to unify criteria in installations as sensitive and extensive as city irrigation and, therefore, the application of these solutions to pre-existing installations must be applied with the necessary care and foresight.

It is fair to say that, as far as Spain is concerned, Barcelona is undoubtedly the spearhead in the application of this type of solution from the municipal approach, since it initiated the application of vertical gardening as a city-wide solution with the development of the Plan de medianeras promoted by the Municipal Institute of Urban Landscape (IMPU), which began with the Tarradellas garden in 2011, the Plan de medianeras 2016-2017 and 2020-2021.
In 2022, the Parks and Gardens Department has taken on the coordination of the maintenance of vertical gardening with an internal management of

The City Council and a reinforcement with the outsourcing of services with a final price excluding taxes in a tendering process of 46.57 €/m²/year.
Other Spanish cities, such as Valladolid, Santander, Bilbao or Vitoria, are also contemplating some emblematic works, as well as Valencia, where pilot tests have been carried out and monitored. The plan for Madrid (Madrid + Natural) is laying the foundations for future applications of nature-based solutions in the Spanish capital, where we can already find iconic works such as Caixaforum Madrid.