Water access at the roof level is an important design consideration that is often forgotten or an afterthought in the vegetated roof design process. Access to sufficient water is one of the most important considerations for establishing and maintaining healthy vegetated roofs. After the establishment period, most extensive vegetated roofs can rely predominantly on natural rainfall with occasional supplemental watering needed when natural rainfall amounts fall short.

There is no such thing as a no-maintenance vegetated roof.

Hydrotech highly recommends that a maintenance contract be in place on all vegetated roofs. Maintenance is critical during the establishment period to help ensure the long term success of a project.

The amount of maintenance needed on vegetated roofs taper down as the plant material becomes more established and mature. Vegetated roofs cannot perform as intended without maintenance.

Aside from the thrive and coverage warranty that Hydrotech can provide if we supply the vegetation, there are additional reasons Hydrotech strongly recommends maintenance. Below are key points that need to be considered.

• Vegetated roofs are a significant investment. Maintenance is a relatively small cost to protect this investment.
• Keeping a watchful eye on the roof will maximize plant health, maintain the aesthetics of the roof, and ensure any systems such as drains, parapets, vegetation free zones and irrigation systems are performing as designed.
• Healthy plants transpire water which is an essential function on vegetative roofs to manage stormwater, keep the roof cool and help mitigate the urban heat island effect.
• If the vegetative roof is not maintained invasive weeds can take over a roof. This not only can lead to an unsightly roof but the specified plant material could completely die out and be taken over by invasive species. Some invasive species have aggressive root systems which could potentially compromise the waterproofing membrane.

Please contact Hydrotech's Garden Roof Department for additonal information about best maintenance practices.

What vegetation option is right for your Extensive Garden Roof?

Vegetation selection requires understanding a wide range of factors, including microclimates, which could ultimately affect the success of a vegetated roof project. Hydrotech has 20 years’ experience on vegetated roofs all across the country and can assist in vegetation selection for your project based on your design intent.

Hydrotech offers a wide variety of extensive plants including perennials as plugs and sedums in several formats including cuttings, plugs, and pre-vegetated InstaGreen® Sedum Carpets and InstaGreen® Sedum Tiles. Each planting method allows for various degrees of design flexibility and coverage rates. Each method has particular requirements for establishment and maintenance

Hydrotech offers city specific plant lists which can be used as a great starting point for your vegetation selection. These lists include natives, grasses and succulents appropriate for your projects location.

Vegetation selection factors include:

A majority of plant life functions best when there is ample water and favorable temperatures. However, with the exception of tropical regions, most plants are exposed to dry periods and/or temperatures below freezing for some period of time during the year. Unlike animals, plants do not have the ability to add insulation through fat stores or a winter coat, nor do they have the ability to relocate. Instead, plants go through a period of dormancy.

Dormancy is a state in which plants exhibit little or no growth and in which most, if not all metabolic activity ceases for a period of time. It is typically triggered by cooler weather and a reduction in sunlight, but also can be brought on by stress due to heat or drought. These changes in climate are nature’s mechanisms to inform the plants that they need to start shutting down for the upcoming winter months. The plant goes into dormancy at this time because it can no longer make enough food from photosynthesis to support active growth.

Nearly all plants in temperate regions go dormant in winter, including those on your Garden Roof. Most deciduous plants, including some sedums, shrubs, and trees, lose their leaves in preparation for dormancy, in order to protect themselves against upcoming damaging weather conditions. With the onset of freezing temperatures, deciduous plants must protect themselves against water freezing and then rupturing their cells.

Evergreen plants also go dormant, but less conspicuously than their deciduous counterparts. While evergreen trees and shrubs do not grow, pollinate, or produce seeds during dormancy, they retain their leaves or needles. This holds true for some species of evergreen sedums, which will hold onto their foliage, but typically take on an orange or reddish color during dormancy.

The onset of dormancy emphasizes the importance of ensuring plants are properly established and healthy heading into the winter months. Ideally, plants within newly installed landscapes have the opportunity to get established for at least a few weeks, and uptake water into their roots and stems and (evergreen) leaves part of their normal processes. This water will prevent the plants from drying out during dormancy. If plants do not have the opportunity to establish and uptake water, they will dry out and are then susceptible to desiccation or winter burn.

Although dormancy can be considered a quiet time for your Garden Roof, many plants provide winter interest throughout the winter months. Evergreen sedums turn orange, red, and brown, ornamental grasses provide color and texture, and woody plants even without their leaves, can provide structure. A plants dormant state and how it can contribute to the aesthetic of your project should be considered when designing your Garden Roof.

Dormancy will come to an end in spring, the weather starts to warm and the days get longer, and plants can resume their normal processes. Spring is typically a great time to check nutrient levels within the media, which should be amended as necessary based on the type of plantings. This will ensure plants have all the vital nutrients for a successful growing season.