Room With a View
For city-dwellers, rooftops are particularly valuable areas. They can be transformed into congenial rooftop gardens for sunbathing, entertaining, al fresco dining and areas for children to play (provided that there are adequate safety barriers).
Creating a Rooftop Room
Try to create a room-like atmosphere so that you feel you are sitting in the roof space as you would a room, rather than perching on it, since the enormity of the sky overhead and a view stretching into the distance can be rather overwhelming. Painting walls, replacing or covering the original roofing material with weatherproof flooring or lightweight paving, lighting for the evenings and furniture will all make rooftop gardens more congenial. Planting can then be used to add a refreshing touch of greenery and color that will soften the stark lines of surrounding buildings.
Because roofs are exposed to the elements, permanent planting must be resilient, or given shelter from strong winds. A convenient water supply and regular maintenance are vital to their success because the wind has a dehydrating, foliage-burning effect and container-grown plants have a limited moisture reserve.
Always consult your landlord and/or a structural engineer before using a roof or making any structural changes to it. Heavy elements are best sited over or close to direct structural support—usually the edge of the roof space.
The Best Rooftop Plants and Flowers
Plants on roofs, balconies, and high window ledges are exposed to far greater extremes of heat, cold, and wind than those at ground level. The wind not only buffets plants, but dehydrates the soil in which they are grown—an effect intensified by the sun. However, there is a considerable range of plants that are able to survive such inhospitable conditions, and many others that can survive a season, or longer, if shelter is provided by a fence, canvas windbreak, or tough shrub, such as a form of juniper. Plants grown in containers (as those grown above ground level are likely to be) have a limited nutrient and moisture reserve, so always use a nutrient-rich, moisture-retentive potting mix and water frequently.
Tough Permanent Planting
Tough, shrubby material can be used to give year-round interest, and to shelter you and your less-hardy plants from the wind. Look to those that are adapted to survive conditions on open ground, such as on heaths, mountainsides, or by the sea. All the brooms are tough (Cytisus spp., Genista spp., and Spartium spp.), as are the gorse family (Ulex spp.), various heaths and heathers, evergreen and “evergray” herbs, most conifers and many grasses. Climbers in exposed locations are likely to take a considerable beating from the wind, so stick to deciduous ones (these are naturally tougher than evergreens), such as Virginia creeper (Parthenocissus spp.) and honeysuckle (Lonicera spp.). Alternatively, use resilient evergreen climbers like ivy (Hedera spp.).
Plants for Seasonal Interest
Many plants will survive a season on a rooftop, window ledge, or balcony, particularly if they can be given shelter and are well cared for. Mass spring and summer bulbs and annuals in containers to add a flamboyant dash of seasonal color. Plants with a daisy flower are usually tough; these range from the smallest blue daisy (Felicia spp.), through to the exuberant yellow Rudbeckia spp., and a long-standing favorite, white Leucanthemum x superbum.