A balcony or rooftop garden has advantages and challenges. Enough sun is commonly not a problem for rooftops but might be for balconies. Snails and slugs and many other creeping insects or pests are usually not a problem. But wind and accessible water can pose challenges.
Here are basic and important considerations when considering balcony or rooftop gardening:
- Weight: Will the balcony or rooftop support the weight of people, containers and pots, soil, water, and crops? Consult a structural engineer or licensed contractor to be sure the balcony or roof terrace can bear the load. Load-bearing areas are usually around the edge of a roof or above internal supports. Balconies are often suspended from the side of a building and can not bear heavy weight. When placing containers on a balcony or roof spread the load around and use lightweight containers and a soilless growing mix.
- Wind: The higher your garden, the more likely it will be exposed to wind. Wind can suck moisture from both plants and containers. Choose wind-tolerant crops—generally low-growing vegetables such as lettuce and greens, carrots, potatoes, and dwarf bush beans and herbs such as bay and rosemary. Screens of woven reed or bamboo and trellising can stifle wind and protect plants. High-walled containers and plants set down in soil that does not fill the container can help limit wind exposure. If pots are lightweight it may be necessary to secure them to railings or fixtures.
- Sun: Vegetables and herbs demand sunshine, but high gardens can get too much sun exposure—plants can get sunburned and require extra water. Shade cloth and shade screens may be needed to protect crops. Retractable fabric awnings can be used or containers that can be easily moved to shaded areas on hot or windy days. Survey your balcony or rooftop in the morning, midday, and afternoon before deciding where to locate your containers.
- Water: Balcony and rooftop gardens require access to water—whether from a hose bib, faucet, or watering cans carried to the garden. Consider the effort required to keep your crops watered when you locate containers. Balconies and rooftops should have a slight fall so that rainwater (and irrigation) can drain away. Check the gradient of your surface before locating containers; water will seep from pots and containers and should flow to a drain. Rooftops should have secure waterproof membranes—protection that has not been pierced or compromised—so that water does not puddle and drip into the building. Rainwater can be collected in barrels, but be sure the structure can bear the added weight.
- Railings and Barriers: Balcony and rooftop terraces should have a secure barrier around the edges to keep visitors safe. Make sure railings are firmly in place. If you secure containers, trellises, awnings, or wind screens to railings or banisters be sure weight does not compromise them. Be sure that planters are not so close to railings that children can climb on or over them.