Plant Primer

Green roof plants need to be tougher and less nutrient reliant than regular ground garden plants because their growth zone and engineered growing medium is lighter, less rich and more porous than natural soil. Exposure to sunlight, wind, shade and temperature puts greater stress on a roof plant. Low-growing, shallow rooted perennial plants that are heat, cold, sun, wind, drought and disease tolerant that possess a long-life expectancy or ability to self propagate with minimal nutrient and maintenance requirements are best suited. This is a tough standard to meet, especially if variety and winter interest is sought.

Plants that are highly flammable (dried out grasses) and those that are excessively "thirsty" are not advised. Also, high nutrient dependent plants that result in high rates of nutrient loading are also undesirable.

Perennials are desirable because they offer color, texture and seasonal variability, but need deeper substrates and moisture. They usually have a higher biomass which usually means more weight load. However, some herbaceous perennials are generally longer lived and more heat and drought resistant. Examples are Petrorhagia, Dianthus, Phlox, Campanula, Teucreum,  Allium,  Potentilla,  Achillea, Prunella, Viola, Origanum because they have shallow roots.

Hardy succulents are ideal for soil mediums less than 4". They have the ability to survive drought, wind stress and possess the ability to store water for extended periods. Sedum, Sempervivum, Talinum, Jovibara and Delosperma favor non-irrigated systems. But be careful, as excessive moisture favors root rot!

Grasses require a higher medium and possess greater biomass. Some may pose a fire risk during winter dormancy. Appropriate shorter grasses are Festuca, Carex, and Deschampsia. others are Andropogen, Bouteloua, Sesleria and Sporobolus.

Herbs such as Thymus, Origanum, Salvia and Allium in less than 4" of medium have worked well, but will require irrigation.

Herbaceous perennials have a limited flowering period and lose their leaves in the winter. Hardy succulents are generally evergreen and may exhibit colored or textured foliage. A mix of hardy succulents, herbaceous perennials and annuals may be combined to achieve year round interest.

Wherever possible, native plants are preferred. These are highly resistant to damage from indigenous diseases and insects and generally require minimal care being adapted to the local climate.

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