Three rules for rooftop gardens: a safe structure, a light soil mix and good drainage. Get those right and the rest is habit.
1. Before you start: weight and safety
Wet soil weighs roughly 1,500 kg per cubic metre, so a 30 cm layer adds about 450 kg per square metre. Not every residential roof is designed for that. Spread small pots across the roof rather than filling it with soil, use a light mix, and consult an engineer if unsure.
- Put heavy containers over walls or beams, not mid-span.
- Check railings; never leave children alone.
- Never block roof drains.
2. Choosing containers
| Soil depth | Container | Suitable crops |
|---|---|---|
| 15–20 cm | Trays, small buckets | Red amaranth, spinach, coriander, lettuce, small radish |
| 25–30 cm | Large pots, sacks | Chili, brinjal, capsicum, okra |
| 40 cm+ | Drums, cut barrels | Tomato, gourds (with trellis), lemon, guava, papaya |
3. A light soil mix
By volume, roughly: loam 30–40%, compost or aged manure 30–40%, the rest coco peat, rice husk or sand. Coco peat and husk reduce weight and hold water.
4. Drainage and roof protection
- Drill drain holes in every container.
- Raise pots on bricks or timber so air moves below and the roof isn’t left wet.
- Repair cracks and waterproofing first.
- Don’t let water stand in saucers — it breeds Aedes mosquitoes.
5. Watering and wind
Roofs get more sun and wind, so soil dries fast. Water early and late in hot weather, mulch the surface and use bottle drip. Secure trellises and stakes before nor’westers and shade young seedlings.
6. A weekly routine
| When | Task |
|---|---|
| Daily | Water, check under leaves for pests, pick ripe produce (10 minutes) |
| Weekly | Weed, trim yellow leaves, check saucers for standing water |
| Monthly | Mix compost into pots, replace finished plants, check trellises and ties |
See the work calendar and crop guide for what to plant each month.