How Auburn University horticulturists help rooftop plants thrive

Prepare to welcome plant guests

Before the first plant sprouted in the rooftop garden, scientists and architects were plotting for their arrival. 

“It’s not like we came into an existing building and figured out how to put a garden on the rooftop,” Layne said. “It was actually architecturally designed specifically for that purpose.”

The 4,400-square-foot area designated for the garden is about the size of a basketball court, with specific growing zones throughout it. Rather than using raised beds one may see in a community garden, the architects created concrete-walled growing zones with drainage systems underneath.

“These different growing zones are like their own individual swimming pools that are full of this growing substrate that is a commercial product that has to be lifted up onto the rooftop by a crane and effectively spilled out onto these growing areas,” Layne said.

Once the planting beds were ready to go, scientists decided to bring small transplants up to the roof, instead of seeds. “That way, we’re ensured that the plant is going to establish, and it will be sooner for it to come into production,” he said.

Here comes the sun – and the rain

Plants that prefer to grow in full sun are in luck on the rooftop. For other plants that would need a little shade to grow well, scientists get creative. 

“As a Department of Horticulture, we know what plants do well in the sun and which ones require shading, so we have that level of the knowledge from the get-go,” Layne said. 

Tall sunflowers can serve as a helpful shield from the sun for a smaller plant neighbor. The sun’s placement throughout the day can give the garden’s edges temporary refuge. 

But sometimes, no amount of creativity can salvage the situation.

“Any plant that doesn’t do well in full sun, if you put it up there, it will probably cook,” said Layne.

Rooftop plants also contend with rain. Too much rain, and the plants will drown in it. Too little rain, and the plants can’t grow. Layne said a team of scientists and students monitor the plants and tweak the irrigation system to find the Goldilocks water spot. 

“They’re constantly going around and visually assessing the health of the plants and whether or not they look drought-stressed,” he said. “They can easily check the moisture of the soil.”

If a plant requires more water, they can turn on the irrigation system or even add additional emitters in a location that needs it. 

Bring on the bees and a little luck

Running a rooftop garden requires a tolerance for the unexpected. Take last year, when Layne said temperatures dropped to about 15 degrees for three consecutive nights and wreaked havoc on the rooftop plants.

“We had plants that were killed. It was unavoidable, so it’s one of those acts of God situations where we’re going to observe it, take notes about it, and we’ll plan to come back at the end of January and replant the whole space,” he said. 

While luck wasn’t on the team’s side with the freezing cold weather, they’ve had good fortune with pollinators. 

“We’re on the seventh story of a building in one of the tallest places in the city of Auburn and within a couple of days of putting plants up there, we had bees and hummingbirds,” Layne said. 

The pollinators received a warm reception, while pests and other insects would be less welcome rooftop guests. 

“Being on a rooftop certainly doesn’t isolate us from problems,” Wells said. “We have many, if not all, of the pest and disease pressures that are typical for gardens, but we do our best to stay ahead of trouble.” 

Some ways the team stays proactive includes investing in growing healthy plants that can be resilient to pest intruders, maintaining helpful bug populations and staying vigilant for any potential problems, Wells said. 

A little science goes a long way

The rooftop is a reliable garden, churning out produce and flowers; it’s also a place where science is in action. 

Scientists and students are currently collaborating to investigate approaches to increase rooftop plants’ uptake of nutrients and conservation of resources. 

“Rooftop substrates are inherently porous to allow for water movement and to reduce load on the building, but that can come with some downsides,” Wells said. 

These cons include higher water use and less nutrient uptake by the plants, Wells said. Mackenzie Pennington, a master’s student advised by Wells, is examining whether a mushroom-based compost can help lock in nutrients and water for the root zones to extract.

“The idea is to add compost in thin layers over time to the surface of the substrate. This will help hold more water and nutrients near the surface, which will help young plants acclimate quickly and will help us conserve resources,” Wells said. 

On top of her novel graduate work, Pennington also manages about 15 student workers. She says her applied work in the garden has put her “one step ahead” when she graduates. “I’ve learned more this past year working in the garden than my whole five years in college before this,” Pennington said. 

Pennington says she especially enjoys collaborating with the chefs and the Horst Schulze School of Hospitality Management efforts a few floors below. The rooftop garden gives students from both horticulture and hospitality the unique opportunity to collaborate and learn from one another’s expertise. 

From cutting-edge research to funneling food to a student-run restaurant, the rooftop garden is attracting interest from scientists across the country. 

But Layne also hopes the garden has a big impact closer to home.

“Hopefully when people come up there, we give them an opportunity to see something beautiful, to be refreshed, to maybe think about what they could grow in their backyard,” he said. “Maybe they will think about buying some zinnia seeds and taking them home so that they can have beautiful flowers just like they saw on the rooftop.”