Designing and Maintaining Living Walls To Boost Biodiversity

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*Habitat Horticulture Exterior Living Wall at 2177 3rd St. in San Francisco, CA. This wall attracts honey bees, moths and bumble bees through strategic planting (3)*

Introduction

Exterior living walls should be looked at as a “swiss army knife”of a solution when it comes to combating the effects rapid urbanization has on local ecology. These systems offer a myriad of benefits, but an often forgotten benefit is a living wall’s ability to increase biodiversity through thoughtful design and strategic planting.

How to Support Pollinators with Green Walls

With all exterior living walls, the horticulture and design team should be mindful of the climate and local ecology that the living wall will inevitably contribute to. This means, not only planting native species that will thrive in local zonal conditions but also creating food stops and safe havens for our migratory species throughout the seasons. This is particularly important in states like New York and New Jersey which are located along the Atlantic “Flyway” for many bird species and butterflies that migrate during the spring and fall (1). Here are five important design and maintenance principles for more biodiverse exterior green wall projects.

*Urbanstrong’s rooftop living wall in Chelsea, NYC featuring pollinating species such as Heuchera, Foam flowers, and Columbine*

1. Choosing the right living wall system- choosing a system with a soil based design or water retaining growing medium, such as felt or rockwool systems, can support a wide variety of plant species. This increases opportunities for pollinating friends to stop off at your living wall. Whereas, wire mesh or cable-like trellis systems that can only support a view climbing species of vines won’t be as effective.

2. Selecting the right plant species- for optimal success, plants should first be selected according to their climate zone and weather conditions. Some of the factors to consider are sun exposure, water needs, wind, and elevation. Afterward, we should consider which native plant species best support our pollinating populations! Realizing what pollinators you want to attract and what is viable, given the site conditions is a great start. For example, adult butterflies appreciate full sun environments and butterflies in general like less windy conditions (4). In addition, bumble bees can fly at higher elevations than many other bee species, like lower light conditions and in cooler temperatures, making them excellent pollinators for large scale living walls in dense urban areas (2).

3. Diversify the plant palette- incorporating varying native species versus just featuring a monoculture, can be measurably more effective. Providing a balanced diet of both pollen and nectar is also important to meet our pollinators nutritional needs (5). This can be achieved through a diverse array of plants listed below. The more colorful wildflower clusters and different shaped flower heads incorporated will only further encourage frequent visits and lingering from bees, moths, butterflies, hummingbirds, flies and more! When drafting your plant key, please remember to think about more than just the summer growing season. Pollinators need nectar early in the spring, throughout the summer and even into the fall. So choosing plants that bloom at different times will help ensure consistent visits from our pollinating friends.

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*ANS’s nesting boxes to act as a safe haven for migratory species (7)*

4. Think outside the box- some living wall designers have gone as far as incorporating nesting and beehive boxes in their designs to encourage migratory species to stop off at their wall. These nesting hotels are perfect for bees, birds, and bats looking for a safe haven to recharge.

5. Plant maintenance- we know living walls need standard maintenance for long term plant health and to sustain aesthetic goals set by the clients and designers. In addition to trimming/pruning, the method of deadheading spent flowers and stems will encourage new blooms which your pollinating friends will appreciate. Pesticide treatments can often be part of a living wall maintenance plan but of the pesticides, insecticides can be the most harmful to pollinators. Beneficial insects, manual removal and traps should first be considered as a treatment, making pesticides a last resort. If pesticides are being used, pay careful attention to when they should be applied. Examples of application may be post bloom or late evenings after foraging traffic has passed.

These five principles can help you incorporate support for biodiversity into your exterior green wall project, and in so doing provide critically important support for a wide variety of insects and birds that are struggling due to the negative impacts of urbanization.

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Lily Turner, WELL AP, Director of Green Walls at Urbanstrong, which specializes in green walls. Reach out to Lily Turner at lturner@urbanstrong.com

Designing and Maintaining Living Walls To Boost Biodiversity

Introduction

How to Support Pollinators with Green Walls

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