Choosing the Best Native Plants for Rooftop Gardens

by Tammy Sons – November 18, 2024

A rooftop garden can make a building much more pleasant.  These gardens keep a building cooler in the summer and warmer in the winter.  They improve the air quality, extend the useful life of a roof, and add beauty and color to urban areas.

Rooftop gardening is primarily done with buildings that have a flat roof, although sodding the roof and planting flowers can be done on slanted roofs.  Before buying your plants, it is important to make sure the rooftop can carry the extra weight of a garden.

Condition of the Roof

While it is possible to construct a rooftop garden on a normal city roof, it is not ideal.  You have to take into account all the roof’s flaws.  Water seeping in from the roof, roots growing into the roof, or other damage is common.

The best time to construct a rooftop garden is when the roof is being replaced or built.  This allows you to incorporate a water-proof membrane over the hard roof surface to protect the building below.  A root-resistant layer keeps roots from growing through the water membrane, creating leaks.

Structural Capacity of the Roof

Soil weighs a lot, especially when wet.  Add plants and the framing for each bed and the weight of a rooftop garden adds up.  You must hire a structural engineer or architect to examine the roof and decide how much additional weight the rooftop can support.  If the roof cannot take much weight, you may be limited to a few containers of native plants that live off of rainfall.  You can retrofit the roof to carry additional weight, but it is costly.

If the building is under construction, you can design the roof to hold a rooftop garden.  Installation is easier when it is a part of the construction, too, since cranes can lift the materials for the garden onto the roof without having to go through the elevator or stairs.

Access to the Roof

Access to the roof includes getting the garden supplies up to the roof.  Walking up several flights of stairs with lumber, soil, and fertilizer stops being fun very quickly.  In addition, most fire codes require two ways to exit the roof in case of fire.  This can be a fire escape, stairs, or access to the next building over.  Many rooftop gardens include a small greenhouse to start seeds in.  Greenhouses need electricity and the whole garden will need water so make sure those are available before planning yoiur garden.

Weight of the Garden

rooftop garden

An architect or landscape design architect needs to determine the weight of the kind of garden you want on your roof.  This takes into consideration the weight of water, soil, containers, heaters, cooling, ventilation, and, if it snows where you are, snow load.  You don’t want to get this wrong or your rooftop garden may become a basement garden.  You also have to consider how many people can be on the roof at one time.  Here are some estimates that the City of Chicago published for rooftop gardens.

  • Water stored in tanks weighs about 8 lbs/gallon.
  • Extensive green roof systems weigh about 20-34 lbs/ft2.
  • Intensive green roof systems weigh about 80-150 lbs/ft2.
  • The City of Chicago Municipal Code requires at least 30 lbs/ft2 for the design snow load.

An extensive green roof system is one where you use pots and some hardy plants for a garden.  It does not need as much infrastructure as an intensive green roof system.  An intensive green roof system is most like a raised bed garden on a normal lot.

Cost

A green roof system costs about 50% more than a conventional roof.  However, it extends the life of the roof by at least 50%, keeps cooling and heating bills lower, and looks nicer than a conventional roof.

Your budget needs to include the containers, cost of a structural engineer or architect for determining roof load and overseeing construction, safety features such as rails around the edge of the roof, transportation of materials to the roof, soil, an irrigation system, and the cost of permits and fees.  You should also include maintenance costs.  Some locations offer cost sharing if you put in a rooftop garden that meets their requirements because of the lower energy costs and pollution, but you will need quite a sum to get started.

Designing a Green Roof System

A green roof system has many components.  The bottom layer is the roof deck.  A waterproof membrane is next, then a root barrier to stop the roots from growing into the waterproof membrane.  A layer of insulation comes next, followed by a drainage layer that is gravel.  This gives the water from rain, snow, and irrigation of the garden a way to drain out of the growing media above it.  Next there is a filter mat that keeps the growing media from running out with the water as the garden drains.  Finally, there is the growing media, the plants, and a wind blanket to hold the growing media on the roof until the plant roots grow into it and prevent the wind from blowing it away.

Irrigation

Using plants native to the region you live in will decrease the need for irrigation.  However, there are times even drought tolerant plants need help, so you should provide a way to water your plants.  Drip irrigation is the best option, but a spigot for hand watering is the cheapest.  You will need to hire a plumber to extend the water system in the building to the roof.

Drainage

Drainage is essential to prevent the garden from damaging the roof and building.  Poor drainage not only causes the roots of your plants to rot, it adds substantial weight to the roof.  Most rooftop drainage systems can be used with minor tweaks.  Again, consult with a structural engineer or architect for help making sure your rooftop garden has good drainage.

Choosing Plants and Growing Media

Soil is heavy.  Most rooftop gardens use light weight growing media for their plants to grow in.  Typically, it is compost and lightweight, porous material that absorbs water and then releases it back to the plant as the plant needs it.  This medium is often referred to as potting mix, as it contains no soil.

Native plants fare best in rooftop gardens because they are adapted to the amount of rain the area receives.  Pick plants that can tolerate the wind, which can be substantial if the building is very tall.  Pick plants that are happy in poor, dryer soil so you do not have to fertilize them much.  You will have to water the plants the first year at least once a week until they are established.  The wind dries the soil and plants quickly, so a plant will require more water than the same plant in a garden on a regular lot.  Prairie plants such as purple coneflower, black-eyed susan, and blanket flower, since they can handle the wind better than something ephemeral, like a Virginia bluebell.

Maintenance

Plants need tending in a rooftop garden, just as if it were ground level.  Drains and gutters on the roof will need to be inspected more often than roofs without a garden.  Larger plants and trees will have to be pruned to prevent branch breakage in the wind.

We Can Help

TN Nursery specializes in native plants from across the United States and Canada.  Our specialists can answer your questions about choosing plants for your rooftop garden.  Simply call us at 931.692.7325 to get started.

Products from the article

Purple Coneflower - TN Nursery

Purple Coneflower

Purple Coneflower - Echinacea  Purple coneflowers are a favorite in the garden for their beauty, ease of maintenance, and hardiness. They’re perfect for those who enjoy an attractive, pollinator-friendly perennial.  Purple Coneflower Soil Recommendations These plants prefer rich soil and full sun but will also tolerate some shade. Planting these long-living perennials is simple: you make a hole rather than bury the root ball in the soil and water it. Once established, they do not require much maintenance or attention, not even watering when it’s still dry. They are drought-tolerant and pest-resistant and attract pollinators like bees and butterflies. Seasonal Beauty and Blooming Cycle of The Purple Coneflower They are known to bloom throughout the summer and late fall. The purple-pink petals of each bloom cluster around a coppery-orange cone. Winter dries up the flowers, and decorative seed heads appear in winter to attract birds. The bloom season lasts many weeks after summer arrives. Even into late fall, birds and monarchs feast off these plants.  Shape and Longevity Of This Stunning Perennail  Purple Coneflowers are tall, graceful plants growing two to four feet tall. They are striking because of their daisy flowers and their somber green leaves. The perennials are perennial and can endure for decades when cared for appropriately, thus offering an excellent, stable, and durable option for any garden.
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Black Eyed Susan - TN Nursery

Black Eyed Susan

Black-Eyed Susan: Rudbeckia Hirta Black Eyed Susan has vibrant yellow petals and dark, contrasting centers and is a popular and delightful addition to any landscaping project. This native North American wildflower offers a host of pleasing attributes that make it a sought-after choice for gardens and outdoor spaces. From its adaptability to its visual appeal and ecological benefits, it stands out as a versatile and attractive plant.  Black-Eyed Susan Plants Attract Pollinators Rudbeckia Hirta is a beautiful and popular flower that blooms each year in North America. With yellow flowers surrounding a dark circular center, this plant serves an aesthetic purpose in any landscape and draws in bees and butterflies. Due to its hardiness and versatility, the plant is suitable for growing in the garden for beginners and professionals.  This perennial is valued for ornamental purposes and contributes to ecosystem maintenance.  Features of the Black-Eyed Susan The perennial has bright yellow petals with a dark brown or black Eye in the middle, making it a vivid plant that would look great in any garden. This plant attracts bees, butterflies, and many other beneficial insects, so it should be included in any pollinator garden. It is relatively adaptable. It does well in arid conditions and simple soil types, making it a perfect pick for any low-maintenance garden.  Pollinator Favorites It prefers regions receiving full or partial sun exposure. Its growth habit is 2 to 3 feet tall and similar in width, enhancing the green appearance of areas where it is grown. Once established, this plant does not need much attention and usually grows well.  It is relatively immune to many garden pests and diseases. Growers of this plant can also contribute to habitat and care for one's patch of land by offering food for pollinators and other more valuable insects. Returns Every Warm Season Buy them and add these beautiful flowers to your garden, like our other popular ornamental plants, such as echinacea, shasta daisy, or coneflower plants. Growth Enhancements and Suggestions They do well in regions with full sun exposure. Ensure they are exposed to at least six hours of sunshine daily. They like well-draining soils and will grow in a range of soil types. These perennials symbolize encouragement, motivation, and justice. Their bright yellow color with a dark center is linked with positivism and strength, making them perfect for any garden.  Fertilizing Isn't Necessary, But Here are Recommendations They are native plants that do not require fertilizer, but you can use a slow-release fertilizer if you prefer it. Use it sparingly as they grow because these plants are not heavy feeders.  Maturity Height and Bloom Cycle  Depending on their type, they are perennials that can reach 1 to 3 feet. They provide great accents to borders and garden landscapes. Black-eyed Susan plants can take from 60 to 90 days to bloom after germination from seeds. The plants return year after year, blooming mid to late summer and continuing into early fall.
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Blanket Flower - TN Nursery

Blanket Flower

Blanket Flower - Gaillardia  Blanket flower is the perfect choice when you’re craving warmth. This radiant wildflower with an extended blooming season will light up your garden with a kaleidoscope of glowing colors. How Did Blanket Flowers Get Their Name?  Multiple legends surround the name. The simplest indicates that it comes from these flowers' tendency to blanket the ground with vibrant blooms quickly.  Another suggests that the name comes from how thriving patches of these flowers are reminiscent of brightly patterned Native American blankets. One story links the inspiration for the flower’s name to the gorgeous blooms that repeatedly appeared on the grave of a talented Native American weaver famous for creating richly hued blankets. Bloom Colors of the Vibrant Perennial They are available in an array of hot colors. Yellows, oranges, peaches, reds, maroons, and burgundies are common. The flowers are intensely colored and framed by silver-green foliage that’s slightly hairy. With blanket flowers, the color is vivid and long-lasting. These plants bloom repeatedly throughout the summer and into the fall. What Do Blanket Flowers Look Like? With so many species of this plant, there’s lots of variety. Generally, these flowers have daisy-like flowers that feature multiple rays around a central disc. These rays can be in a single or double layer. There may be flat or trumpet-shaped petals.  Some flowerheads offer a single, vibrant hue. Others boast bands of colors, resulting in a striking ombre effect. This sun-loving perennial sends up stems with a single bloom measuring between two and four inches. The plants typically reach heights of 12 to 18 inches, but they can grow up to 36 inches tall. When To Plant Blanket flowers are a wonderful way to add more color to any space, and their blooms last well in gardens and vases. They are heat—and drought-tolerant and withstand deer, rabbits, and groundhogs while attracting bees, butterflies, and birds. Their ability to blanket the ground with a carpet of color makes them a popular choice for borders, roadside plantings, and ground covers. They also thrive in rock gardens, cottage gardens, and pollinator gardens.
From $8.49
From $8.49
Purple Coneflower - TN Nursery

Purple Coneflower

Purple Coneflower - Echinacea  Purple coneflowers are a favorite in the garden for their beauty, ease of maintenance, and hardiness. They’re perfect for those who enjoy an attractive, pollinator-friendly perennial.  Purple Coneflower Soil Recommendations These plants prefer rich soil and full sun but will also tolerate some shade. Planting these long-living perennials is simple: you make a hole rather than bury the root ball in the soil and water it. Once established, they do not require much maintenance or attention, not even watering when it’s still dry. They are drought-tolerant and pest-resistant and attract pollinators like bees and butterflies. Seasonal Beauty and Blooming Cycle of The Purple Coneflower They are known to bloom throughout the summer and late fall. The purple-pink petals of each bloom cluster around a coppery-orange cone. Winter dries up the flowers, and decorative seed heads appear in winter to attract birds. The bloom season lasts many weeks after summer arrives. Even into late fall, birds and monarchs feast off these plants.  Shape and Longevity Of This Stunning Perennail  Purple Coneflowers are tall, graceful plants growing two to four feet tall. They are striking because of their daisy flowers and their somber green leaves. The perennials are perennial and can endure for decades when cared for appropriately, thus offering an excellent, stable, and durable option for any garden.
From $8.99
From $8.99
Black Eyed Susan - TN Nursery

Black Eyed Susan

Black-Eyed Susan: Rudbeckia Hirta Black Eyed Susan has vibrant yellow petals and dark, contrasting centers and is a popular and delightful addition to any landscaping project. This native North American wildflower offers a host of pleasing attributes that make it a sought-after choice for gardens and outdoor spaces. From its adaptability to its visual appeal and ecological benefits, it stands out as a versatile and attractive plant.  Black-Eyed Susan Plants Attract Pollinators Rudbeckia Hirta is a beautiful and popular flower that blooms each year in North America. With yellow flowers surrounding a dark circular center, this plant serves an aesthetic purpose in any landscape and draws in bees and butterflies. Due to its hardiness and versatility, the plant is suitable for growing in the garden for beginners and professionals.  This perennial is valued for ornamental purposes and contributes to ecosystem maintenance.  Features of the Black-Eyed Susan The perennial has bright yellow petals with a dark brown or black Eye in the middle, making it a vivid plant that would look great in any garden. This plant attracts bees, butterflies, and many other beneficial insects, so it should be included in any pollinator garden. It is relatively adaptable. It does well in arid conditions and simple soil types, making it a perfect pick for any low-maintenance garden.  Pollinator Favorites It prefers regions receiving full or partial sun exposure. Its growth habit is 2 to 3 feet tall and similar in width, enhancing the green appearance of areas where it is grown. Once established, this plant does not need much attention and usually grows well.  It is relatively immune to many garden pests and diseases. Growers of this plant can also contribute to habitat and care for one's patch of land by offering food for pollinators and other more valuable insects. Returns Every Warm Season Buy them and add these beautiful flowers to your garden, like our other popular ornamental plants, such as echinacea, shasta daisy, or coneflower plants. Growth Enhancements and Suggestions They do well in regions with full sun exposure. Ensure they are exposed to at least six hours of sunshine daily. They like well-draining soils and will grow in a range of soil types. These perennials symbolize encouragement, motivation, and justice. Their bright yellow color with a dark center is linked with positivism and strength, making them perfect for any garden.  Fertilizing Isn't Necessary, But Here are Recommendations They are native plants that do not require fertilizer, but you can use a slow-release fertilizer if you prefer it. Use it sparingly as they grow because these plants are not heavy feeders.  Maturity Height and Bloom Cycle  Depending on their type, they are perennials that can reach 1 to 3 feet. They provide great accents to borders and garden landscapes. Black-eyed Susan plants can take from 60 to 90 days to bloom after germination from seeds. The plants return year after year, blooming mid to late summer and continuing into early fall.
From $8.99
From $8.99
Blanket Flower - TN Nursery

Blanket Flower

Blanket Flower - Gaillardia  Blanket flower is the perfect choice when you’re craving warmth. This radiant wildflower with an extended blooming season will light up your garden with a kaleidoscope of glowing colors. How Did Blanket Flowers Get Their Name?  Multiple legends surround the name. The simplest indicates that it comes from these flowers' tendency to blanket the ground with vibrant blooms quickly.  Another suggests that the name comes from how thriving patches of these flowers are reminiscent of brightly patterned Native American blankets. One story links the inspiration for the flower’s name to the gorgeous blooms that repeatedly appeared on the grave of a talented Native American weaver famous for creating richly hued blankets. Bloom Colors of the Vibrant Perennial They are available in an array of hot colors. Yellows, oranges, peaches, reds, maroons, and burgundies are common. The flowers are intensely colored and framed by silver-green foliage that’s slightly hairy. With blanket flowers, the color is vivid and long-lasting. These plants bloom repeatedly throughout the summer and into the fall. What Do Blanket Flowers Look Like? With so many species of this plant, there’s lots of variety. Generally, these flowers have daisy-like flowers that feature multiple rays around a central disc. These rays can be in a single or double layer. There may be flat or trumpet-shaped petals.  Some flowerheads offer a single, vibrant hue. Others boast bands of colors, resulting in a striking ombre effect. This sun-loving perennial sends up stems with a single bloom measuring between two and four inches. The plants typically reach heights of 12 to 18 inches, but they can grow up to 36 inches tall. When To Plant Blanket flowers are a wonderful way to add more color to any space, and their blooms last well in gardens and vases. They are heat—and drought-tolerant and withstand deer, rabbits, and groundhogs while attracting bees, butterflies, and birds. Their ability to blanket the ground with a carpet of color makes them a popular choice for borders, roadside plantings, and ground covers. They also thrive in rock gardens, cottage gardens, and pollinator gardens.
From $8.49
From $8.49
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