Planning my Rooftop Garden

Posted under environment by Jason Roasen

The roof top garden is simply a garden, usually in containers, that is located on a roof top. Any construction - an office, garage or shed, can have a green roof garden if it is substantial enough to take the excess weight and has a suitable surface.

If you’re planning a green roof garden, you should consult a structural engineer to ensure that the roof is waterproof and can handle extra weight of planters, moist soil mixes, decking, furnishings and people.

Deliberate the purpose of the space. If you are looking to grow a container or two of herbs and vegetables that is one thing; or are you planning a garden where lots of people will visit? Or, are you designing an outdoor space for relaxation and entertaining that incorporates flowers, shrubs and trees into the project? I have even seen an orchard on a roof!

Realistically, how much time do you want to spend on your garden? If your time is limited you may want to keep the garden element of the project modest, you can always add afterwards, enough so that you can give the plants the attention they deserve.

The largest difficulty to successful container gardening on a green roof top is powerful winds and hot sun. You need a rooftop water supply, outdoor electrical outlet and storage space for tool and supplies. Roof gardening requires plenty of water, so check how and where the roof drains.

Containers can be made from plastic, terracotta or wood. During the growing season it will commonly be sunny, hot, dry and windy so you must select hard-wearing plants that will tolerate such conditions.

If you’re going to grow permanent plants such as shrubs or small trees or perennials in containers, choose plants that are one or two zones hardier than your climatic zone. For example, if you’re in Zone 5, choose woody plants that are hardy to Zone 3 or 4.

Give some lath-type structures for shade. You can use vine-covered trellising as a wind-break or privacy screen. A trelis or screen must be suitably supported.

Choose drought resistant plants as they will stand up against sun and wind. Many drought tolerant plants have silver or grey-green leaves, their light leaf colour reflecting the harsh rays of the sun. Some have a coating of fine hairs on their leaves or stems, helping to trap moisture around the plant tissues.

A green roof top garden is an ideal place to grow native perennials. This will help the native plant population and they will be able to deal with the climate. This will also encourage native butterflies and birds to drop by for a visit.

To view a number of terrific picture examples of green roofs or for extra help and advice about roofing solutions, visit the ICB website.