Up on the Roof
It is easy to create a luxuriant garden on a roof terrace. Before you get going, however, make sure that the construction of your roof area is sturdy enough to take all the extra weight your garden will involve. If you are in any doubt, ask an architect or engineer to take a look. When planning the layout, remember to consider some form of sun protection, such as an awning. You will need to consider the effect of high winds and ensure that it is fixed securely.
For plants to do well on the roof, they will need sufficient space for their roots to grow. Choose large containers filled with suitable compost, in a style that suits your rooftop garden. A rustic wooden planter has a rural feel, elegant terracotta gives a Mediterranean effect, or ceramic an Asian influence. Remember that stone and terracotta containers are heavy, so choose plastic containers where you can without ruining the effect to minimise the load on your roof.
Make sure your chosen containers are heavy enough to remain stable in high winds. If you want the design to be flexible, put tubs or containers on coasters (platforms on wheels) so that you can easily move the containers around. Good drainage is also important so that rainwater can drain away instead of accumulating in the containers.
Creating Themed Areas
Just as in a normal garden, a roof garden can have areas devoted to different types of plants. You may want to create colour-themed areas or planting combinations that evoke a particular style, but remember that roof gardens are often subject to extreme weather conditions, such as fierce winds and intense heat and sun and the plants you choose must be able to withstand this. Seed mixes such as those offered for wild-flower meadows, containing corn flowers (Centaurea cyanus), field poppies (Papaver rhoeas) and corn-cockle (Agrostemma githago), are particularly suitable. The latter are short-lived species that grow naturally in cornfields and are quick to self-seed. In conventional gardens they will not produce a long-lasting wild-flower meadow, but they perform well in rooftop situations. A hedge planted with viburnum, serviceberry (Amelanchier) or wild roses (Rosa canina) can help by screening against wind and creating a sheltered atmosphere.
Choose plants that are undemanding, such as the famous houseleek (Sempervivum): you can create an attractive display in a container with its many different cultivars. These can be accompanied by plants that cope well with drought conditions, such as saxifrages, thrift (Armeria maritima), stonecrops (Sedum) and the many small grasses available that will bring movement to the garden as they sway in the breeze.
A Refreshing Touch
A water feature can be a welcome addition in such a potentially hot spot. As long as your roof can take the extra weight involved, a water feature can be made using large containers such as an old bathtub or half-barrel, but any watertight container will do.
Running water features, such as a bubbling stone or a fountain, will add extra sensory appeal. Place a water feature in a shaded, sheltered spot to minimize evaporation and disturbance from the wind.