The most evident planting style attempts to reconstruct a plant community indigenous to the location. Typically, they have relatively modest decorative value and in an urban setting they do not cope as well as the more resistant weed species, however, the particular importance of them is that these plants fit in most with the principle of biodiversity. When such style is chosen in our climate, the almost completely bare winter condition needs to be made friends with!
The vertical gardens that are constructed to imitate nature provide a more designed solution. In this case, indigenous or exotic, deciduous or evergreen plants can be used. In such cases the plants are placed randomly into the system, then after a while there will be some species that develop and some that die. The dominant conditions change continuously; therefore the overall image of the wall will also change.
Modular systems provide solutions for facades depicting figurative images, logos and different patterns. These no longer try to copy nature; these are the vertical version of the built garden in the traditional sense of the word. The different gardening styles can be reproduced just as in a traditional garden.
The most intensive application is the vertical version of flowerbeds, where the continuous winter-summer flower show can be ensured by swapping annual and bi-annual plants.
Climbers – without a support structure
Ivy (Hedera species): a very low demanding evergreen plant, although in hard frosts it can lose its leaves. Little nutrient is required, it can be planted in sun, half-shade or shade, but in a windy position its development is slow. There are many species with deep green or variegated leaves and various shapes. The copious leaves can grow up to 15 cm in size, covering each other. It uses its aerial roots to climb the wall, forming a 10-20 cm thick foliage.
Trumpet creeper (Campsis species): it can climb up to 8-10 meters height with its tendrils. It has large, orange, yellow or red-cupped flowers from July to September in clusters. It has average water requirements and likes rich soil. It favours sunny and warm position. It can develop a considerable mass of foliage in both volume and weight, standing some 1-2 meters from the wall. The stems may die back in winter.
Boston ivy (Parthenocissus species): It develops cohesive thin foliage on the façade. Many subspecies exist, the shape and colour of the leaves as well as the growth orientation of the species is the main difference. The autumnal colours of the leaves are very decorative. It can climb up to 20 meters height. It is an undemanding plant, can cope with poor soil and tolerates wide temperature variation. It can be planted to sunny, half-shady or shady positions, although this shows some variations for the species. It uses suckers or tendrils to climb the walls.
Climbers – trained onto a support system
Climbing with tendrils: (clematis, wisteria, Dutchman’s pipe, Russian wine): Large species and breed richness characterises this group. They can develop a significant weight of foliage and some species have spectacular and attractive flowers. Deciduous plants.
Supported plants: (climbing roses, common beans): may require tying in
Winding or twisting: (honeysuckle, hops, morning glory Black-eyed Susan vine, silk vine): In general the foliage is smaller in size than those climbing with tendrils. They have characteristically decorative flowers, some are evergreen (facultative).
Cordons: (grapes): these require biding and for most species, intensive plant protection.
The grass provides a green surface in both winter and summer. It is popular and relatively inexpensive, its operation is well understood, although it requires continuous mowing, which on vertical surfaces is difficult to perform! Green walls tend to use grasses as mature specimen plants or as a temporary decoration.
Typically a green area created based on the example of extensive green roofs, just vertically. It requires little maintenance and minimal care. It tolerates drought well, and only needs watering in extreme cases; therefore, in theory it could be an excellent choice for low cost green walls. Unfortunately we are still waiting for a well-functioning installation.
Annual and bi-annual flowers
They can provide intense decoration, however it requires continuous replacements, so when choosing the carrier system it has to be one that tolerates frequent replacement well (e.g. greenwall.pro).
They have a more modest and shorter flower show than the annual plants; however, the range is wide in leaf colour and appearance. Application options are primarily defined by the characteristics of the façade (orientation, exposure). The rockery plants cope well with full sun, while the shady perennials are best positioned in more protected sites. The herbaceous plants have small rooting zones and live for several years. They can be used in a cassette system as replacing them is easy. Perennials typically live for 2-3 years, perhaps to 10 years, and offer the best solution amongst the annuals and shrubs.
There are smaller and larger plants among them, which, due to their larger rooting zone needs, are less usable than the perennials. As the majority of the species and varieties grown tolerate our winters (and generally this climate) rather well, and they are long lasting, they are still a very valuable group of the plants for green facades. Unfortunately only a few systems can accommodate them. The greenwall.pro system is suitable for accommodating the medium and weak growing species-varieties.
Orientation, sun exposure
These are key questions from a physiological aspect. One of them is the dominant wind direction: the optimal plant orientation of the plants is obviously the side protected from wind. Only a few plants are able to survive the in winter weather on walls where the plants are exposed to the dominant wind direction or sweeping winds. The other equally important factor is the length and strength of exposure to the sun: On surfaces where the average annual direct sunshine is less than 3 hours daily, only explicitly shade tolerant plants can be planted. Where the exposure is over 6 hours, plants that require a sunny position will do the best (summer hot-spells may cause damage). In case of exposure between 3 and 6 hours, plants recommended for half-shady positions are well suited; this is the most successful level for constructing and operating a green façade.
The planting medium can be traditional soil or peat based substrate, organic fibrous medium, foam based medium, mineral-based fibre or mineral based grainy medium. The traditional soil and peat-based mixtures are not considered due to compaction issues. The mineral fibre material also compacts due to the continuous contact with water, while the foam-based medium is broken up over time by the roots, thus the life span of this latter one is short.
The mineral-based grainy mediums provide the best conditions for the roots. These porous mineral materials have a stable structure and the humid environment between the grains ensure a good root climate. In addition, they have good drainage characteristics, there is no weed infestation and create conditions that is not desirable for the soil-dwelling pests. The single disadvantage is that their pH value in general is slightly alkaline, which can be corrected and maintained by setting the pH value of the nutrient medium. The acidic pH of the feeding medium also prevents limescale build-up of the dripping holes.
The volume of the planting medium has to be able to accommodate as much root as is needed for covering the water needs of the foliage. In the case of the pocket systems, the few mm thick felt layer provides this medium. In comparison, the planting medium of the cassette systems can be up to 20 times as much, with implicitly larger buffer effect and more favourable physiological conditions.
Water and nutrients
The key factor for the survival of the plants is appropriate water supply. As vertical gardens are typically more exposed to weather anomalies than their horizontal equivalents, and the frequently mentioned balancing effect of the planting medium is significantly more modest, the continuous, exact and even supply of water to the plants of the green façade is vital. The water requirement of the plants strongly depends on the weather. In a long dry and hot period, their water consumption could be multiple of the normal value, while in permanent rainy-humid and cool weather it could decrease to a fraction of it. The climbing systems with a soil connection are the most fortunate in this aspect, as the roots can reach deep into the ground. The pocket system represents the other extreme; it has increased sensitivity, only one missed irrigation cycle may cause problems. Water supply security can be significantly increased by monitoring and automation.
It is important to note that in the case of green facades, in practice, we cannot really count on the natural rainfall, which is especially true for walls on wind-protected sites.
Nutrient supply on the green façade takes place in an entirely artificial manner, the nutrient providing ability of the hydroculture planting medium is minimal. The composition of the nutrient depends on several factors including the salt sensitivity of the plants, the season as well as the given life stage of the plants. When providing the feeding medium, great care must be taken as the feeding medium meets the rootlets directly and without amelioration, thus even small feeding mistakes can cause severe root damage. The feeding medium prescriptions should be prepared by professionals in all cases.
Living organisms threatening the plants of green facades include pests - caterpillars, insects, mites etc., and different diseases caused by bacteria, virus or fungi. There is no considerable difference compared with the protection of traditional ornamentals. The organic planting mediums can harbour ground-dwelling organisms, while they are less likely to settle in inorganic substrates as the airy structure does not provide appropriate conditions for them. The health of the plants needs continuous monitoring and any threats have to be recognised as early as possible. For protection against pests, it is worth involving a pest control professional, which is also a legal requirement. In a given situation the damage caused by humans may also be significant (including damage caused by pets).
This always depends on the given plant. Climbers have the longest life span, shrub type plants can live for several years with appropriate maintenance: The older parts need to be removed in order to provide room for the new ones. The annuals are best from spring to autumn, the bi-annuals from autumn to spring. The life span of perennials is 3-10 years, while the sedums continuously renew and change.
The most important maintenance task is monitoring and adjusting the water and nutrient supply. The removal of plant parts that have died, dried up due to snow, freezing, mechanical damage or sunburn as well as of blown flowers is included in the continuous maintenance. Any changing and replacement of plants will probably be required sooner or later on all walls; this should be taken into consideration when choosing a system, as the suitability for this of the existing systems is not at all trivial. Pest control problems and failure of the mechanical system may require occasional interventions.
For the more intensive systems (higher decorative value modular solution), continuous weekly monitoring by a competent person is strongly recommended; this can take place on the site or in part by remote control. In case of systems that are closer to nature and more extensive, help from a professional is only required when specific problems arise; the maintenance tasks can be performed by the staff on site. There can be several transitions between these two extremes - the difference between them can be best described by the frequency of visits: accordingly, this can be monthly, quarterly, every six months or annually dependent of the parameters of the wall.
Use of plants
Adaptable to an extensive range of plants
The great strength of the system is that it does not use fixed module dimensions, but variable ones adjusting to the size of the rooting zone required by the different plants. For example, when planting shrubs, the module size can be increased by changing the thickness and/or the overall size of the front of the module. The physically required optimal volume for the roots - the physiologically most important part of the plant - can be ensured in this way in all cases. This is a pre-condition for healthy and strong foliage as well as for a rich flower display. The modules are designed to accommodate all types of plants listed in the general section. This way, planting patterns, where the shrub patches alternate with flowerbeds and grassy areas can be created – all these in one system and one engineering solution.
Instant green surface
The system can also accommodate completely mature plants, thus in green facades at premium locations, where the full decorative value is expected on delivery, full coverage can be provided. In cases of changes or replacement of plants, replacement can be with mature plants, thus full coverage can be ensured without interruption. The distance between the plants has to be scaled with consideration to the final foliage size, so they can provide full coverage. The further developmental characteristics of the plants and the expected formation of the foliage should also to be taken into account. In case of foliage growth, it is possible to remove the plants from the module, like a chess board, thus the neighbouring plants do not suppress one another, whilst still providing satisfactory coverage. This solution permits the green façade to remain the same in several years’ time as per the original design.
The formation of an optimised rooting zone
The parallelogram shaped cross-section and the narrow-tall frontal geometry of the module was designed broadly keeping the growth tendencies of the roots in mind. The geotropic nature of the plant roots suggests that it is physiologically more favourable for the roots if the expansion options within the modules are vertical rather than horizontal. With this cross-section design, it is possible to eliminate the “lower plant” effect described in the “size coordination” section. The horticultural perlite medium provides perfect conditions for the roots; in case of watering being accidentally missed, the vapour from the micropores to the macropores can ensure living conditions for the roots for a long time. If the plants are over watered, due to its excellent drainage, the roots will not be damaged and start rotting. These two effects have been tested by drastic interventions (complete water deprivation for two weeks in hot spells, as well as the addition of water triple the quantity of what is optimal for months) on multiple counts. An additional benefit is it is an excellent insulator in dry conditions, thus in the winter period, when there is no irrigation, it protects the roots from the effects of cold air.
Quick and clean plant replacement
Fast changing of plants is provided by the design of the system, which permits the removal of some modules without dismantling the whole wall - only two screws need to be unscrewed and the module can be lifted out. The plant to be replaced can be simply lifted out and a new plant can be added onsite there and then. All this can be completed in a matter of minutes with the workspace also remaining clean. The characteristics of the system will be unchanged even after unlimited replacements. Additionally, if the owner wishes to completely renew the surface of the green wall, even after 10-20 years it will be possible to do so at low cost, perhaps the replacement of the perlite will be required.
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