Green Roofs: Creating an Oasis for Residents, Not Pests

By Jennifer Brumfield, Training and Technical Specialist, Western Pest Services

When it comes to urban green space, the sky’s the limit–literally. Green roofs are a growing trend in cities across the country, with commercial and residential buildings alike converting their shingles to gardens.

Because of their aesthetic appeal, green roofs can be an attractive amenity to potential or current residents. But having a green roof over your apartment has many environmental advantages as well. In addition to gaining credit toward Leadership in Energy and Environment Design (LEED) certification, a green roof can help your apartment complex reduce energy consumption, filter acid rain, and other air pollutants, and mitigate the heat island effect.

These benefits, however, can be overshadowed by one threat: pest infestations. By understanding the possible pest threats and following these simple maintenance tips, you can create a rooftop oasis for your residents, not for pests.

Step 1: Understand the Pest Threats

Because green roofs are a form of living architecture, they are bound to attract pests. Here are a few of the pest threats you may encounter:

• Roof Rats: Roof rats can be a nightmare for your apartment community, as they are excellent climbers and capable of breeding year-round. Be vigilant about inspecting your roof for signs of rats, including droppings, grease marks (or rub markings), and nests.
• Birds: Pigeons, starlings, and sparrows are attracted to rooftop landscaping due to the availability of food, water, and shelter. The flat surface of a roof also makes an ideal nesting site. Bird droppings are a tell-tale sign of these pests, who are likely to hang out on roof ledges or build nests under plantings.
• Plant-feeding insects: Plant it, and they will come. Plant feeders, such as beetles, caterpillars, and aphids, can be found on plant stems or feeding on liquid within plants. Be on the lookout for the “honeydew sap” these insects produce, which can actually draw in ant colonies.
• Stinging Insects: Nothing attracts hornets, bees, and yellow jackets quite like flowers and water – two common components of a green roof. These pests can build nests inside gutters, bushes, and trees, or on the corners or exterior walls of your building.

Step2: Plan the Design

A successful green roof begins with design. To help avoid future pest problems, follow these steps during the design phase:

• Select your vegetation: When selecting your vegetation, try to avoid plants with fragrant and bright colored flowers as well as plants that produce nuts, seeds, or fruit. It’s also best to avoid mulch (try using landscaping stone instead) and plants such as ivy that may hang over building walls and allow pests to enter through windows. Speak with your pest management provider about which species of vegetation to avoid.
• Location, location, location: Choosing the right location for vegetation is just as important as choosing the right plants. Avoid positioning vegetation near the roof door to avoid giving pests easy access inside when the door is opened.
• Circulate water: Many green roofs include water features like ponds or fountains for aesthetic appeal. Unfortunately, standing water can also be prime breeding grounds for mosquitoes. By constantly circulating this water, you can prevent pests from laying eggs on the surface.

Step3: Practice Integrated Pest Management (IPM)

Integrated Pest Management (IPM) is a common-sense approach to pest control that involves proactive monitoring and maintenance of your green roof. Incorporate the following measures as part of your IPM program:

• Schedule Routine Pest Checks: Regular inspections are essential to maintaining green roofs. A pest management provider can help recognize the early signs of pest problems and recommend control tactics to help correct the issue and ward off any future problems, starting first with non-chemical methods when possible.
• Seal Entry Points: Cracks, holes, and other voids in the exterior of your building can be easy entry points for pests. Minimize their ability to spread to other parts of your building by sealing gaps, particularly around doors, pipes, and fixtures.
• Empty Trash Receptacles: It’s no secret that pests are attracted to food and trash. That’s why it’s important to line and cover trash receptacles and empty them on a regular basis.
• Open Lines of Communication: IPM is most effective when the property management team and pest management professional work together. Make sure your maintenance staff understands your IPM program and the role they play within it. Work with your pest management professional to train your staff how to spot and report early signs of pest activity and any deficiencies that may contribute to pest activity.

If your property is considering a green roof, or if you already have one, be sure to follow a regular maintenance routine and work with a pest management professional to help ensure your roof is a green oasis for residents, not for pests.

Jennifer Brumfield is a Training and Technical Specialist and Board-Certified Entomologist for Western Pest Services, a New Jersey-based pest management company serving businesses and homeowners in major Northeastern markets.