How to Start a Roof Garden

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If you live smack in the middle of a dense urban environment, you may not think you have many gardening opportunities available. But increasingly city-dwellers are looking upward to satisfy their desire for urban gardening. Roof gardens are surging in popularity in many large cities, and the benefits are remarkable. Here are just a few of the paybacks of a roof garden, and how you can create your very own urban oasis.

What is a Roof Garden?

Although the name might suggest a few pots of greenery stuck on the top of an apartment building, there are many different ways to have a roof garden. Once you start thinking outside of the traditional garden bed, you’ll find unexpected places that can be used for planting. Wherever you put your garden, it’s important to have a source of water handy. Here are some of the spaces that can be used for gardening.

roof garden

The walk-out roof of an urban multi-story dwelling. This is the classic picture of a roof garden. City-dwellers find space on the top of apartment or office buildings and fill it with greenery. This can take the form of a few flower pots in one area, or several raised beds that cover the roof.

roof garden

Balcony gardens. People who live in apartments but don’t have access to the roof can also create a garden space with containers on the balcony. You can grow a surprising number of plants in a small space with the right containers and planning.

roof garden

Vertical gardens. Not all gardens have to be flat! With the right structure, you can grow plants right up against a wall. This technique can be used for a wide range of plants, from easy-care succulents to vegetables and herbs. The right selection of plants looks like a living mosaic that can be hung on an indoor or outdoor wall.

roof garden

Sloped roofs. With the right structures in place, a garden can blanket the roof, creating a sweep of greenery that covers the entire surface. This is not only beautiful, it helps insulate the roof. Since this isn’t the kind of garden you can walk around on or tend frequently, it generally uses hearty succulents that require little care. 

roof garden

What Can a Roof Garden Do For the Environment?

Gardening is well known as a healthy activity. It’s a relaxing form of exercise, and harvesting your own fresh food is both good for you and satisfying. For people who live in cities, there are added environmental benefits of urban gardening.

Reduces city “heat island” effect. When the sun shines on the concrete and asphalt surfaces of a big city, the heat is reflected back to warm the air. During the summer, this causes a large mass of hot air that makes cities so stifling. A roof garden reduces this effect through shade and evaporation. While a regular roof can be 90 degrees hotter than the air, one covered in greenery is cooler.

Stormwater management. Another problem in big cities is the stormwater runoff. With very little soil to absorb rain, a heavy storm can cause so much water to accumulate that sewers overflow. However, a roof garden can hold 50 to 60% of the rainwater that falls on it. This water then evaporates harmlessly back into the atmosphere.

Insulation. A layer of plants and soil acts as insulation, absorbing the heat of the sun in the summer and holding in the building heat in the winter. Roof gardens have been shown to reduce the need for cooling during the summer and for heating during the winter.

How To Get Started.

Sounds pretty great, right? If you’re ready to get started on your own roof garden, there are a few steps to go through before you get your hands dirty.

Make a plan. Take a look at the space available. What kind of sun does it get? What about wind exposure? Every gardener knows how exciting it is to imagine your garden, full of greenery. But be practical about how much you can maintain. It’s better to start small and then add on once you feel successful. Sketch out where you would like your garden to go, and how large it will be.

Get permission. Who do you need to talk to? It depends on your situation, but some of the places you should check with are your landlord, the homeowner’s association, and the local ordinances and building codes. Local garden organizations are a great source of information about the regulations you need to meet.

Assess the structure. You need a structural engineer to come check out the loading capacity of the roof, and if you’ll need reinforcements. Not all roofs are designed to hold the extra weight of a garden. Many architectural firms have a structural engineer on staff. An architect can help you too, but they will be a bit more expensive.

Get your supplies in order. Figure out how you can get your materials up to the roof, and if there’s anywhere handy to store tools and supplies. Water is another issue to work out. Is there a spigot that you can attach a hose to, or can you capture rainwater in a barrel? If you have to haul all the water your garden needs up to the roof, you may want to keep your garden pretty small.

roof garden

It’s Time To Plant!

Prepare your “land.” To keep the weight of your urban garden as low as possible, use lightweight materials. Containers should be made of plastic or fiberglass. The bottom layer inside the container provides drainage to keep the garden from being soggy. Use a lightweight material such as styrofoam, plastic jugs, or crushed nut shells. The soil should be made with additives such as peat moss, vermiculite, or perlite.

Pick the right plants. Select plants that will do well in your climate. Generally, a roof garden will be hotter and windier than normal conditions. Whether you’re planting an edible garden or an ornamental garden, choose plants that are heat- and wind-resistant. Consider how much upkeep they require to be sure you can devote the time they’ll need.

Plant and protect! Get your hands into that beautiful soil and plant your urban garden. Once all your carefully selected plants are tucked into their new space and well watered it’s time to protect them. A good layer of mulch will keep them from drying out quickly. If the wind is very strong, consider adding a windbreak.

Nurture and enjoy. Because of the exposed nature of a roof garden, it will need to be watered more often. Container gardens also need a little extra care with frequent fertilizing. But a benefit of roof gardening is that you will not have to worry about deer or rabbits nibbling your plants. One of the joys of gardening is the peace of standing in your oasis, your feet cooled by the dripping hose, drinking in the peace. This is what all your work has been for. Enjoy!

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