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Green Roof Plant Blog

Early flower on Green Roofs

Green Team at Green Roof Technology, - Thursday, April 11, 2013

Photo Credit: Sempergreen

To spot a crocus popping up from the ground is a sure sign spring is right around the corner. Many varieties of Crocus are the very first to bloom in the season, although there are a handful of varieties that are autumn blooming plants. A part of the Iris family, these perennials have over 80 different species. They enjoy partial to full sun and well drained soils and flourish in hardiness zones 3 through 9. Growing only 3-6" tall, the cup-like flower comes in a variety of colors such as pink, orange, yellow, blue, white or purple. They require little to no maintenance and can be popular with bees at a season where other plants are not flowering yet. In the language of flowers, the crocus means cheerfulness.

Many are cultivated for their flowers appearing in autumn, winter, or spring.

The spice saffron is obtained from the stigmas of Crocus sativus, an autumn/fall-blooming species and could be an interesting crop for semi intensive green roofs or educational urban farms.

Some Crocuses or Croci especially C. tommasinianus and its selected forms and hybrids (such as 'Whitewell Purple' and 'Ruby Giant'), seed prolifically and are ideal for naturalizing on green roofs.

Photo Credit: Sempergreen

The picture above shows Crocuses planted under a pre-vegetated Sedum mat at the Sempergreen facility and below shows them planted in between plants of the Convention Center Parking Garage in Philadelphia among other bulbs.

Photo Credit: Green Roof Technology

Thymus serpyllum - Wild Thyme

Green Team at Green Roof Technology, - Tuesday, March 26, 2013

Photo Credit:

Wild Thyme is a low, creeping herbaceous perennial. Only growing to about 4" tall, this evergreen shrub makes for great ground cover. Although native to Europe, Asia and Northern Africa, Thyme has been naturalized in most of North America. Spotted growing in between zones 4 and 8, the plant will flourish in full sun with average to well-drained soils. Soggy soils can make Wild Thyme susceptible to root rot. In early summer a sea of purple flowers appear. These clusters of flowers may range from lilac to magenta. Don't let the tiny appearance of these flowers fool you, they are strongly scented, giving off an herbal-like lemony scent. The flowers attract wild honeybees and butterflies. In Europe the Large Blue Butterfly relies on the presence of Wild Thyme because they feed almost exclusively on it.

The leaves are oval and slender, with a slight glossy appearance. The oil found within the leaves is an antiseptic, disinfectant, expectorant, and a diuretic. It is most commonly used to treat respiratory infections, but is also used to fight cramps & spasms, cuts & ulcers, headaches or weak digestion. Thyme is also a popular herb used in the culinary arts and may also be made into tea.Thyme is one of many valuable plants that is suitable for urban farming on bio-diverse non-irrigated extensive green roofs in less polluted areas.


Tulipa sylvestris

Green Team at Green Roof Technology, - Tuesday, March 12, 2013


Also known as the woodland or wild tulip, this fragrant, sunshine yellow flower was first recorded in Europe.  Easily naturalized in fields, it can be found mostly in the north eastern United States in hardiness zones 3-9.  Growing anywhere from 4-12", this tulip is comfortable in full sun or partial shade and grows best in well drained soils.  Blooming in mid to late spring, the wild tulip has the ability to clone itself by underground stolons, running horizontally and popping up several feet away.  These runners help this bulbous perennial to spread easily over any landscape. Ironically these woodland tulips have been slowly disappearing in the wild.


Oenothera biennis

Green Team at Green Roof Technology, - Thursday, February 28, 2013

The Common Evening Primrose has yellow, lemon-scented flowers that bloom in late spring to summer, but only show their bright petals when the sun is hiding. They open late at night into the early morning, but have been known to stay open for days if the sky is cloudy.  Although they shy away from the sun at its brightest, don't get the wrong idea, this plant lives best in full sunlight and well drained soils.

Native to North America, this biennial can grow rather tall and take on a bushy or weedy appearance. The leaves are long and thin, like those of a willow tree. One large taproot keeps this plant in place, which is also edible; if boiled it may be eaten similar to potatoes. The wind helps to establish new populations by carrying around the tiny brown seeds to a new places. Hummingbirds, Hawk moths and Japanese beetles all favor the evening primrose and can often be found nearby.  

Bleeding Hearts for Green Roofs on Valentine‘s Day?

Green Team at Green Roof Technology, - Monday, February 11, 2013

by Jorg Breuning

As beautiful as the Greek name sounds, Dicentra eximia is relatively undiscovered by the Sedum-blinded Green Roof plants experts and by the yearning LEED point collectors. The beautiful flower is native Genus to Northeast United States and Asia that comes in many “faces” (Species and several cultivars).

Dicentra eximaThis plant won’t survive in full sun but will thrive on moisture retaining partially or fully shaded roofs with in a FLL-certified green roof growing media with depths around 3-5 inches.

Leaves are finely divided and gray-green, growing from the base of the plant.

Flowers are pink and bloom in tight clusters at the top of leafless, fleshy stems above the leaves from mid-spring to autumn. The four petals are connected at the base. The two outer petals are pouched at the base and bent back at the tips. The inner petals are perpendicular to the outer petals and connected at the tip. The pistil is enclosed within the inner petals, and the two stamens are on either side. There are two tiny, triangular, pink sepals above the petals.

Seeds are borne in a plump, pointed pod. They ripen to black while the pod is still green. Each has a white elaiosome (Greek élaion "oil" and sóma "body") that is prized by ants.


If the ants would have been a litter quicker in the last 150,000 years these plants would have spread over the entire North America already.  However, with green roofs there is a chance to help nature along in this process.


USDA Dicentra Eximia

Viola sororia Willd.

Green Team at Green Roof Technology, - Tuesday, January 29, 2013 

The common blue violet is a low growing herbaceous perennial, native to Eastern North America.  Clusters of showy purple, blue or white flowers bloom throughout the summer. These flowers often attract butterflies. The foliage is a bright green, with serrated leaves resembling the shape of a heart.  It enjoys sunshine and grows best in between hardy zones 3 and 7. Easiest when grown in average, well-drained soils.  This plant may be sowed now, any time between November and March. If favorable growing conditions, this little violet has the potential to spread rapidly.

The violet was viewed as a symbol of love and fertility by the Ancient Greeks along with modesty and innocence by the Romans. The flowers and young leaves of this plant are edible, but described as bland tasting, although they are rather rich in vitamins A and C.    

Geranium sanguineum - The Bloody Cranesbill

Green Team at Green Roof Technology, - Tuesday, January 15, 2013

 By: Samantha Yurek

 Photo Credit: Wikipedia

This geranium blooms a bright magenta in the summer, but turns a crimson in the fall, which is where the name Bloody Cranesbill was derived from. A herbaceous perennial with fern-like leaves, this variety of geranium enjoys full sun and well-drained soils with low nutritional value.  Although native to Europe, this plant is far from invasive and makes for great green roof ground cover. The hardiness zones for this plant are 3-8.

This is a green roof plant that can be seeded right now! The geranium is best sowed between November and March.

These plants are easy to expand on your rooftop garden by cloning.  Cloning can be completed in several ways.  Cuttings are a practical and inexpensive way to expand the plant cover on any rooftop garden. 

  • Stem cuttings: in which a piece of stem is part buried in the soil, including at least one leaf node. The cutting is able to produce new roots, usually at the node.
  • Root cuttings: in which a section of root is buried just below the soil surface, and produces new shoots

These cuttings should then be buried in the green roof growing media or spread under a pre-vegetated mat

 Learn more on how to get started with cuttings today!


A Cool Green Roof Plants Study

Green Team at Green Roof Technology, - Friday, January 11, 2013

Picture: Greenpeace

By Jorg Breuning

A recent British study in Building and Environment found that broad-leafed plants, such as Stachys byzantina, Bergenia cordifolia and Hedera hibernica, which can thrive in partial shade, outperformed the traditional Sedum in cooling the substrate and surrounding air.  The study concluded by suggesting, “…the choice of plant species on green roofs should not be entirely dictated by what survives on the shallow substrates of extensive systems, but consideration should be given to supporting those species providing the greatest eco-system service potential.”1

This is certainly one of the many worthless studies on the web that shows us that no horticultural understanding or common sense was ever part of the research study.  A green roof is all about the vegetation and if we are not entirely dictated to by what survives, we have simply no plants, no vegetation, and therefore no green roof.  It is also not new that more leaf mass provides cooler temperatures – standing in summer in the forest is cooler than on a corn field.  I always thought this was common knowledge. 

The broad-leafed perennials that were tested (less than 2 year tested) typically require deeper soil profiles.  More green roof growing media (soil) increases the costs of the green roof, the structure and the maintenance dramatically.  Substantially increasing green roof costs decreases the likelihood of having a green roof to start with.  The study also did not mention that the climate conditions in Great Britain are unique and are generously supported with moderate temperatures by the golf stream all year around.  This effect allows higher varieties of plants to start with but won’t guarantee a higher survivability of these plants.

Comparing Sedums with the mentioned type of perennials is like comparing wild strawberries with apples. The survivability of Sedums under extreme conditions on a shallow layer of soil with low nutrients makes them to the ideal, perennial and stabilizing groundcover for extensive green roofs.

There is no doubt that we use other annual or perennial plants as temporary fostering or nursing plants or to promote the growth of Sedums or reduce the pressure of unwanted plants. 

In modern green roof technology there are multiple choices of herbaceous perennial plants that supplement the fundamental Sedum carpet.

Botanical Names of Green Roof Plants

Green Team at Green Roof Technology, - Monday, January 07, 2013

A botanical name is a formal scientific name to each individual plant conforming to the International Code of Nomenclature for algae, fungi, and plants (ICN). The purpose of a formal name is to have a single name that is accepted and used worldwide for a particular plant or plant group.

Botanical NomenclatureFor example, the botanical name Sedum reflexum denotes a plant species which is native to Northern, Central, and Southwestern Europe, where it has accumulated various names in many languages. Later it has been introduced worldwide, bringing it into contact with even more languages. English names for this plant species include: Reflexed Stonecrop, Blue Stonecrop, Jenny's Stonecrop and Prick-madam. The cultivar Sedum reflexum 'Blue Spruce' is a blue-green-variegated horticultural selection of this species.

Botanical names prevent people from confusing different species of plants, but also indicate that different species are related. The genus (ex. Sedum) is the unique name followed by the species (ex. reflexum). The first letter of the genus is capitalized and the species in small letters. Most of these names have their origin in Latin or Greek, are combinations of languages or words, the name of somebody who is honored, appearance or location.

Knowing what the Latin (and sometimes Greek) words mean can help gardeners with their planning and maintenance chores. For instance, if the available area is cramped, a plant with arboreum (tree-like) or altissimum (very tall) in its name might not be the best choice.
Some names refer to special characteristics of the plants. Pubi, hirti, villi, and barbi are all "combining forms" suggesting hairiness. Combining forms are Latin roots with vowels added to facilitate pronunciation. They frequently appear attached to more familiar Latin-based words, like those for leaf and flower. Hirtifolia would mean hairy leaved. Barbiflora would mean bearded flower.

It is getting really interesting when we look at cultivars of plants like Sedum reflexum 'Blue Spruce'. 'Blue Spruce' is a blue-green-variegated selection of this species. Variegations of plants can be caused by environmental conditions (air quality, sun light, nutrients, water supply etc.) or by targeted human influence like propagating only the plant with certain properties, propagating plants with “defects” or Gen manipulation (like most of our food plants, ornamental plants or turf grasses).

Vegetation for Green Roofs should be identified, specified and communicated by their botanical name to avoid confusion. The names of the plants must be written correctly according the International Code of Nomenclature and professionals don’t refer to the “Latin” name of a plant – they refer to the botanical, horticultural or formal scientific name of plants.

Recommended readings (Multi-lingual):

•• Zander - Handwörterbuch Der Pflanzennamen / Dictionary of Plant Names / Dictionnaire Des Noms Des Plantes: Dictionary of plants. Dictionnaire des noms des plantes [Hardcover]
•• The Timber Press Dictionary of Plant Names

Recommended readings (only English):

•• Mabberley's Plant-book: A Portable Dictionary of Plants, their Classifications, and Uses [Hardcover] An Aid to the International Code of Botanical Nomenclature

Hieracium aurantiacum

Green Team at Green Roof Technology, - Thursday, January 03, 2013

By: Samantha Yurek


Also known as the Orange Hawkweed or Devil's Paintbrush, this brightly colored plant is commonly categorized as a weed in many North American countries.  Native to the alpine regions of Europe, these perennials tend to grow extremely close together, forming a dense evergreen mat-like structure and avoiding erosion. Eventually these long flowering plants form a natural weed control blanket by blocking the way for other plants.  They grow fast in soil with low organic matter like Green Roof growing media and have a high tolerance for frost and drought, making them an ideal plant for a green roof.  A summer blooming flower, this plant will sure to add some color to your roof!

Many types of Asteracea like Senecca and Hieracium, are valuable foraging flowers for many native bees like this Megachile species. 


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