A rented balcony can hold a useful little garden if you plan around three limits: how much weight the slab can carry, how much direct sun it gets, and what your lease lets you fix to the building. Get those right and herbs, salad leaves, chillies and flowers will grow happily in pots.
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Check How Much Weight Your Balcony Can Carry
Find out the load limit before you buy pots, because wet soil is heavy. The Weather Network puts wet soil at about 1,600 kg per cubic metre, which is roughly 1.6 kg for every litre of pot you fill. By its figures, a planter about 30 cm deep packed with wet soil can press close to 500 kg onto each square metre it covers.
Compare that with the standard the same report cites from BC Housing in Canada: residential balconies there are designed for non-permanent loads of 40 pounds per square foot, about 195 kg per square metre. Your building will have its own figure, so ask the landlord or managing agent for it. The Royal Horticultural Society (RHS) warns that balconies built out from the side of a building have strict weight limits and advises asking a chartered structural engineer or surveyor what a roof or balcony can take.
Placement matters too. The RHS suggests putting heavy containers near load-bearing walls or over a load-bearing beam, so ask the landlord where the wall and beams sit before you line big pots along the railing.
Choose Light Containers and Potting Mix
Plastic, fibreglass and lightweight metal pots are the RHS choice for balconies. They are lighter than clay, and the RHS notes that soil in non-porous pots dries out more slowly than soil in terracotta, which helps on a hot, windy ledge.
Fill them with bought potting mix, not soil dug from a garden. Oregon State University (OSU) Extension says garden soil and topsoil can be too heavy for containers and may hold too much water. The RHS adds a trade-off: soil-based compost holds water better than a peat-substitute mix but weighs more, and pots filled with lighter compost may need fixing so they don’t blow over. It also suggests a layer of polystyrene in the bottom of pots to help drainage and cut weight.
What Size Pot Each Plant Needs
Ten-inch pots (about 25 cm across) are big enough for herbs, parsley and spring onions, according to OSU Extension. Tomatoes, peppers and eggplant (brinjal) need five-gallon containers, which hold about 19 litres. At the Weather Network’s 1.6 kg per litre, a full 19-litre pot of wet soil weighs around 30 kg, so keep the big ones for the crops that need them and park them near the wall.
Get the Drainage Right
Every container needs holes so extra water can escape. OSU Extension suggests drilling holes along the side about half an inch (just over 1 cm) up from the bottom of a pot that has none. Drilling your own pot is fine in a rental; drilling the building is a different matter.
Lift pots off the floor on bricks or pot feet so they don’t sit on concrete or in a saucer of water, which OSU Extension also recommends. The RHS gives the same advice for roof gardens, so roots don’t get waterlogged.
Think about where the run-off goes. Water drips through to the balcony below, so use trays where you can and water slowly when neighbours are sitting outside.
Pick Plants for the Sun Your Balcony Gets
Count the hours of direct sun on a clear day first, because light decides what will crop. Fruiting crops such as tomatoes and peppers need 6 to 8 hours of direct sun a day, says OSU Extension, and more is better. Iowa State University Extension lists many leafy crops and herbs that cope with light shade, and is blunt about the limit: no vegetable, fruit or herb will be productive in full shade.
| Light on your balcony | Direct sun a day | Plants to try |
|---|---|---|
| Full sun | 6 to 8 hours or more | Tomatoes, peppers, strawberries, annual flowers and most container herbs (OSU Extension, The Weather Network) |
| Light shade | 4 to 6 hours | Lettuce, kale, Swiss chard, rocket (arugula), bok choy, radish, peas; herbs such as mint, parsley, chives, coriander and basil (Iowa State) |
| Moderate shade | 2 to 4 hours | Strawberries and some cane fruit tolerate light to moderate shade, per Iowa State |
| Heavy shade | Under 2 hours | Iowa State says no edible crop will be productive here |
High balconies are often windy as well as sunny. The RHS recommends plants with narrow, grey or waxy leaves, and grasses, whose narrow leaves let wind pass through. A slatted or mesh screen slows the wind without the turbulence a solid screen can cause.
No-Drill Ideas That Leave the Building Alone
You can add growing space without a single screw in the wall by using freestanding, stacking and hanging set-ups. Some that fit a rental:
- Railing planters and hanging bags. The Weather Network lists window planters, hanging plants and bags hung from walls or railings among ways to fit more plants into a small space.
- Stackable planters. The Weather Network includes these too. They use height instead of floor area; stand them against the wall of the flat, where the RHS suggests heavy pots go.
- A trellis tied to the railing. The RHS suggests training climbers up a trellis on the railings from pots below. Cable ties or garden wire hold it without drilling.
- Long, low troughs. The RHS says containers with a low centre of gravity are less likely to blow over, and long, low planters work well.
- Ties for tall plants. The RHS advises fixing taller plants and climbers securely to rails.
Read the lease or building rules before you hang anything over a railing, since some blocks ban it. Keeping planters on the inside of the rail is the sensible default, so nothing can fall on people below.
Water and Feed Little and Often
Plan on watering every day in hot weather. OSU Extension says container soil dries out quickly, especially in full sun, and advises watering when the top of the mix feels dry, until water runs from the drainage holes. The RHS says balcony plants may need watering twice a day in summer, and points out that a balcony overhead can stop rain reaching your pots at all.
Potting mix runs short of nutrients fast. OSU Extension suggests a water-soluble fertiliser every three to four days at half the label strength, or a dry fertiliser every three weeks. Check the pack for the product you buy, and repot crowded plants in spring as the RHS suggests.
Sources
- RHS: Roof gardens and balconies
- RHS: Balconies and roof gardens
- The Weather Network: How you can transform a small balcony space into a large garden
- Oregon State University Extension: Container gardening, grow vegetables even without yard space
- Iowa State University Extension: Growing edible plants in shady areas
