The Q&A Archives: Roof top garden

Question: How do I go about planning for a roof top garden for youth?

Answer: Rooftop gardens deserve some real consideration so I'm glad you asked!

A simple rooftop garden can be created with planting containers or potted plants.
This kind of garden is the most common for homeowners to construct because they
are relatively low in cost and easy to maintain. A container garden provides the
benefits of reflectivity, shade, and evapotranspiration. Compared to a green roof
system, it is not as effective at insulating or reducing stormwater runoff.
A more elaborate rooftop garden is one where the garden actually becomes the roof.
In that case, specially designed layers separate the garden from the ?hard? roof,
provide drainage, supply nutrients, and even add contours. This type of rooftop
garden is referred to in the industry as a ?green roof system.?

There are two types of green roof systems ? ?extensive? and ?intensive.? An
extensive green roof weighs less than an intensive green roof. It generally has
shallower growing material and heartier plants that require little maintenance.
Intensive green roofs are the most like gardens on the ground?with deeper
growing material, more intricate or delicate plantings, and more maintenance
needs such as irrigation and pruning.

The type of rooftop garden you design depends partly on your interest in gardening
and maintenance, and on the environmental benefits you wish to achieve.
Most importantly, you must evaluate the structural capacity of the building in order
to assess your options.

Since natural soils are heavy, particularly when wet, rooftop gardeners typically use
lightweight growing media consisting of high-quality compost and recycled
materials. The purposes of these materials are to be water permeable, to retain water
and air, to resist rot, heat, flying sparks, frost and shrinkage, to provide nutrients appropriate to the chosen plants, and to provide a rooting medium.

Generally, the growing media should be as deep and have as great a volume as possible within the constraints of the structural capacity, in order to provide plants with stability in wind and keep the system from becoming too dry.

Rooftops can be hostile environments for plants due to the effects of wind, heat,
rain, and shadows. Extra insulation may be needed inside and/or outside of
planting containers to protect plants from freeze/thaw cycles in winter. A rule of
thumb is that wind speed doubles for every ten stories of building height. Windy
conditions increase the loss of moisture from growing media and leaves, so
drought-tolerant plants often survive best. Many plants, especially native varieties,
are suitable and attractive options for rooftop gardeners.

As for what to plant, you might want to ask the youth what they'd most like to grow - flowers, vegetables, fruits - and then research each of the plants to see whether they will be able to adapt to the conditions the garden will provide.

Hope this information helps!

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