It is the question we get asked most, and the honest answer is: it depends on the building, and you should check.
Austrian standards typically design residential balconies for an imposed load of around 400 kg per square metre, but older buildings and cantilevered balconies can be lower. Your property manager or the building plans will have the figure.
What things weigh
- Wet potting compost: roughly 1 kg per litre.
- A 60-litre planter, filled and watered: 70 to 80 kg.
- A 120 cm raised trough: easily 200 kg.
How to reduce weight
Use lightweight fibreglass or plastic containers, fill the bottom third with expanded clay instead of soil (only for deep pots), and put the heaviest items near the wall, not at the edge.