PLANT ZONING
In the NATIVE PLANTS? Pattern we discuss that the distinction between native and non-native plants and consider that the difference may not be as definitive as implied. We describe the ecological advantages of using native plants but also consider that non-natives may be appropriate in some locations. Here we will discuss how both native and non-native plants might be used.
ZONES
When designing landscapes, we like to approach plant selection based on planting zones related to the degree to which the site is altered by humans. Inside the building, where the environment is the most highly tempered, plants requiring the most effort to maintain might be used. Then, as we move out from that building, transitioning to the yard and garden, then out through the larger compound and finally to the edge of cultivation and development, plants transition to more native species.
In the building, tropical conservatory plants that require supplemental lighting and careful temperature and humidity control can help enliven interior spaces. At the garden adjacent to the building, where the landscape is obviously the result of artifice, non-native and hybridized plants might be incorporated. Moving beyond the boundaries of the garden or yard where human interaction with the landscape becomes more stewardship than design, native species should be used exclusively. Since native plants are often less showy than non-natives or hybrids that have been selected for their impact, the resulting landscape will have more formal specimens with more dramatic ornamental features in the garden zone and more irregular plants that naturalize more easily at the landscape edges as is appropriate.
In practice this approach often results in a landscape where the majority of the plants are native, but non-native or hybridized plants boost the impact of the landscape at the garden zone adjacent to the house.
CLEAR BOUNDARIES
The use of non-natives should be limited to areas that are obviously manipulated. We find that if the transition from tempered to un-tempered is more subtle, with the aim of merging the architecture with the larger natural landscape, non-native plants should be used very sparingly immediately adjacent to the structure or avoided completely. When there is a more defined edge between the “garden” and the larger landscape beyond such as a boundary wall, fence, hedge or mown edge, less native plants may be appropriate.
IN THE CITY
Applying this principal to the city scale, non-native plants are a welcome resource in dense urban conditions where the environment is highly tempered including as street trees, in building courtyards and on roof terraces. Since the urban condition presents some of the most challenging growing conditions, a wider latitude for plant selection is often helpful in these locations.
At urban edges, parks and along naturally configured watercourses intersecting the city, the more natural condition demonstrated with native plants and the plant communities they form should reassert itself to highlight that the city is overlaid on an underlying natural landscape.
EXCEPTIONS
Finally, Plant Zoning describes a general approach prevalent in many of our projects. There are some projects where plants are selected counter to this approach to achieve a particular design affect. This might include native plants with a very irregular habits arranged in geometric rows next to a building or native and non-native plants of related species planted in adjacent beds to contrast their attributes. An urban building courtyard might have all native plants so the green space appears as a remnant of a preexisting landscape.