In New York City, access to the outdoors is especially prized, and a rooftop terrace, where you can plant real trees, is perhaps the ultimate find. But putting trees on a roof—either full-grown or starting them small—is not the same experience as growing them in a backyard. There are several considerations to be aware of, including wind and weight, and what to do when the roof needs to be repaired and you need to move your trees.
Brick Underground turned to Bob Redman, owner of Urban Forestry and Tree Care in Manhattan, who was recently honored as a “True Professional of Arboriculture” by the International Society of Arboriculture, for his tips on how to install and care for rooftop trees.
What are the first things you need to do?
"You'll definitely need to ask your building management and/or co-op board what is allowed and what the rules and regulations are. Weight is always a concern. As is watering—you'll need an outdoor water supply and hose or to be willing to haul water out to the trees, which is backbreaking," Redman says.
"Take into consideration the type of tree and how large it will grow in a container. You might need fewer for the space than you think you do, and of course the site conditions (windy, sunlight requirements, etc.)."
Is it harder to care for trees in NYC?
"The nurseries here charge a lot more for the logistics of stocking trees in the city, and the trees still need to be delivered and transported to the roof. It's not like the suburbs, where a truck can drop it into the ground with minimal fuss.
"Delivery and installation alone can cost hundreds of dollars here. It also depends on what size tree you're talking about. Many people want to install large trees but I advise them to start smaller, especially in a container, and let the trees grow in situ. It's less expensive, fun to watch them flourish, and trees that grow up in the conditions they'll be living in long-term tend to be more hardy," Redman says.
What are some of the benefits of having a tree on your roof?
"As on the ground, adding shade and visual interest is appealing, but I think for a city dweller, having a slice of nature close at hand really adds psychological benefits. Direct contact with nature can be limited in the city, and having a tree that you can see, touch, and breathe is emotionally uplifting (and studies show it might even improve physical health and promote healing)," Redman says.
Do you need to care for a tree differently on your roof than you would in a backyard?
"Yes, because rooftop trees are in containers. They need even more regular watering than a tree in the ground would, especially during dry, hot weather—it can be a daily task sometimes. Applying a 2-inch to 4-inch layer of shredded bark mulch around the trees will reduce moisture evaporation and improve soil conditions," Redman says.
What are some of the more common mistakes that people with rooftop trees make?
"A common scenario is a rooftop gardener nurtures trees for years and years, and they grow magnificently large ... and then the building needs roof access to replace or repair the roof. The trees can’t be relocated at that point so they need to be cut down. It’s heartbreaking," Redman says.
How can you avoid such heartbreak?
"The weight of a large container, soil, and tree adds up, and it can be difficult or impossible to move them when needed. It's a good idea to have removable deck panels and planters on wheels so they can be moved around in case the roof needs maintenance or replacement.
"Trees also need to be contained, with pruning or sometimes root pruning if you can't transplant them to a larger container. The cold can also be a concern—even if a species is rated for our temperature zone (Zone 6). When a plant is in a container, it has less protection against the wind and cold. I myself have lost my entire bamboo garden three times due to harsh winters—I'm afraid I'll have to try another plant this time. But that's gardening for you! It's trial and error, even for the experts. Sometimes I'm not as sad as I would be when I lose a tree because it frees up space to find a new one!" Redman says.
Do birds like trees on rooftops?
"Once I got to a roof terrace to find a flock of ducks had moved in. And when conditions are right, birds will nest in rooftop trees. A pretty special treat for a city-dweller."
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