Rooftop Gardening: An Overview

With all this time in quarantine, many of us in big cities like New York are starting to get really jealous of suburbanites and all that gardening space they have. But luckily there is a growing demand for putting gardens on an unlikely and often completely unused space, rooftops. Today we’re going to look at everything rooftop gardens, including some surprising unexpected benefits.

Types of Gardens

Rooftop gardens are nothing new of course, from the Hanging Gardens of Babylon to Tolkien novels mankind has always dreamed about greenery covering their roofs. There are a couple different types of gardens though, from simple ones most people can install on their own with enough elbow grease to large-scale construction projects. The simplest ones are built with simple carefully-maintained potted plants, and while the limited and quick drying soil can limit your options on which types of plants to pick, you can still plant everything from beautiful flowers to delicious vegetables. More extensive gardens will put a layer of soil on the rooftop itself, which is healthier for the plants as it allows their roots to grow better, but this option is obviously much more expensive. Finally simple green roofs just put grass on the rooftop. More popular in suburban areas than cities but not unheard of, these utilitarian roofs are designed to get some of the climate and personal benefits of having greenery on the roof with less upkeep. 

Benefits

The environment is going to be thanking you for a rooftop garden. Cities are basically deserts for the animals that live there, and providing even a little extra greenery gives homes, shelter, and resting spots for the animal residents. This is especially true if the garden is made from mostly native plant life, which you probably should be doing anyway to help keep the maintenance down. Plant life also cleans the air, and in urban areas that need this the most this pollution filter can be a life saver, literally. And of course any greenery is a CO2 sink, doing a little bit more to help the fight against climate change.

The first and most obvious personal benefit is having a gorgeous private oasis in a concrete desert. This might be more important than simply unwinding after a long day, as seeing green might be considered a major important aspect to human health. Dubbed the biophilia hypothesis, it argues that as humanity developed in nature and not air conditioned apartments, humans have a psychological need to see large amounts of greenery, and explains why we relax in gardens. Vegetable gardens of course also provide a very direct material benefit, although the normal savings a garden creates for food costs are mitigated by some of the expenses of installing it on the roof, so probably best to only use the cheapest option of potted plants. 

One unexpected but surprisingly good benefit is the energy savings. Traditional rooftop building materials actually increase the temperature of the building by absorbing heat, and so greenery can have significant heat reduction effects. Large buildings can have total heating costs reduced up to 6%, with upwards of 20% for the top floors, with the effects going up to 70% for extremely hot, air-conditioning intense environments. The city of Toronto estimates that a serious garden roofing effort would save the city $22 million, and Chicago puts their city estimate at $100 million.

Considerations

If you’re thinking about starting your own rooftop garden there are several things you need to consider. 

• Permission from your landlord. Obviously this is a must for bigger projects but even if you just have a few potted plants, you still need to be sure on legalities, timing, safety, etc. Dirt and water can get heavy and you don’t want to crack your roof over some tomatoes, nor do you want to see your hard work get thrown out one day because construction was coming that day.
• Costs. Again, a few potted plants is not going to cost much different than any other container gardening endeavor but a fully loaded soil garden can cost upwards of $20/square foot for installation or more
• Water. Lugging a watering can up a flight of stairs or two might not be bad but the more greenery the more watering, so an easy access to water is needed. And if that means a water pump situation it adds to your costs.
• Gardening tools. Biggest issues here are storage and convenience, so plan to also have a little box or build a little shed so you can keep the tools on the roof for easy access. 
• Wind. The higher up a building the harder the wind whips through so you need some precautions. Boxes that are too lightweight or top-heavy risk getting blown around, blown over, or even knocked off the roof. The right type of potting and  windbreak for your situation needs to be a must.

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