Vertical gardening in any climate can be extremely complex. The regional climate, or plant hardiness zone, is the biggest overriding climatic aspect that needs to be considered, along with the neighbourhood microclimate, and the microclimate of the wall itself.
USDA Hardiness Zones in North America, image via Wikipedia
The regional climate plays a big role in determining what kind of vertical garden system is appropriate for a given site. As an example, if the site experiences a long winter below 0°C, a hydroponic system would be out of the question if the garden is to stay in place throughout the winter. These types of systems are not designed to freeze, and if they are installed in colder climates, insulation/heating or complete removal will be necessary to protect the garden during the winter. While most outdoor vertical gardens are designed for warmer climates than USDA zone 5, researchers are currently working on developing a system that works well in colder climates. If you know of, or have worked on, a vertical garden project somewhere colder, please post a comment below to share!
In landscape architecture, we often plan our designs in response to, or for the creation of, microclimates. It is because of them that we are able to plant some species that would normally not be found within the given region. A vertical garden may be highly dependent on the existence of a microclimate for shelter from the wind, lower (or higher) than average temperatures, higher humidity levels, or a variety of other aspects, depending on the location. When planning a vertical garden it is important to know what kind of microclimate you are working within to determine if a vertical garden is appropriate or not, and if so, what kind of plants you should use.
Some of the most important things to consider when designing a vertical garden are: the average temperature (as well as the extremes), wind exposure, sun exposure and ambient humidity and access to water. The average temperature will tell you which plants will be able to survive in your garden, and details like solar orientation and humidity or access to water will further narrow the plant palette.
RELATED STORY: Vertical Gardens: A Brief Introduction
Wall Microclimate, image ©Tamara Urben-Imbeault
The microclimate of a wall is also remarkably complex, ranging from hot and dry, to slightly cooler, and to more moist. A green wall is a gradient of different climatic scenarios, and may vary from wall to wall depending on the surrounding climate and microclimate. Toward the top of the wall there is often increased solar exposure (depending on the prevalence of shadows cast by adjacent buildings), and increased wind. These two factors together frequently result in decreased moisture content in a vertical garden.
There is often more shade towards the bottom of the wall (again due to neighbouring buildings) as well as lower wind speeds which result in an increase in moisture. Water within the vertical garden will also accumulate towards the bottom of the wall, contributing to higher moisture levels. The first storey of a facade will also face increased disturbance from people, animals and passing cars. Between 2 – 7.5m in elevation, dust will be captured on the leaves of the garden: If dust uptake is a priority, plant species with large leaves should be chosen, as the amount of dust accrued is directly relative to the size of the leaf itself.
Climates are extremely complex and constantly changing. With global climate change, weather is becoming increasingly unpredictable, but with the aid of new technology, and programs like Ecotect and Autodesk Design Flow (pictured above), we can further study the impact of the climate on our designs. It is important that we also take the time to visit the site, and make our own notes and observations.
My own personal notes and observations of naturally occurring vertical gardens (cliffs) will be the subject of the next Vertical Garden Series post, which will be published next Thursday, so stay tuned!
Written by Tamara Urben-Imbeault, M.L.Arch. student at the University of Manitoba, Winnipeg, Manitoba, Canada. She is currently working on her design thesis entitled “Vertical Gardening in Cold Weather Climates”
Contact: umurbeni[at]myumanitoba.ca or t.urbendesign[at]gmail.com
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