Chapter 2: Rooftop Gardening — Exam Notes
1. Rooftop Gardening
Rooftop gardening means growing plants on the roof of a house, school or other building using pots, grow bags or specially prepared beds.
Main benefits
- Produces healthy vegetables and other plants.
- Helps cool buildings.
- Reduces air pollution.
- Creates green spaces.
- Provides habitat for animals.
- Helps people connect with nature.
- Useful in cities where open farming land is limited.
Exam point: Even 1 m² of rooftop space can produce about 10 kg of vegetables per year, depending on plant type, method and care.
2. Scoping the Work
Before starting, decide:
- What to grow?
- Select plants suitable for the local agro-climatic conditions.
- Prefer plants with a 2–3 month life cycle for this project.
- Consider sunlight and water requirements.
- Resources required
- Pots/containers
- Soil or growing media
- Investment/cost
- Weight of materials
- Purpose
- Food for meals
- Flowers for festivals/events
- Other useful purposes
- Location
- Decide where the garden will be placed.
- Determine how many pots can safely fit.
Remember
Scope = What + Resources + Purpose + Place
3. Process Chart
A process chart lists the tasks, their expected completion dates and the person responsible.
Major tasks
Layout → Soil/potting mix → Germination test → Sowing → Maintenance → Pest protection → Growth/nutrients → Harvesting → Packaging/transport
4. Designing the Rooftop Layout
Six major factors:
1. Space
Leave enough space between pots for:
- Watering
- Movement
- Maintenance
2. Sunlight
- Select areas receiving about 5–6 hours of direct sunlight daily.
- Partial shade → herbs and leafy vegetables.
- Open sunny areas → tomatoes and cucurbits.
3. Weight & structural safety
Heavy pots and growing media can overload a roof.
- Understand the roof’s load-bearing capacity.
- Heavy containers should be positioned where the structure can safely support them, such as near/over beams as appropriate.
- Weight should be distributed safely.
4. Water management
- Keep pots on trays, tiles or stands.
- Collect excess water.
- Ensure proper drainage.
- Prevent waterlogging and seepage.
5. Shade
Use:
- Shade nets
- Bamboo screens
- Vertical trellises
6. Wind protection
Strong winds can damage plants or overturn pots.
Important: Observe wind direction before finalising the layout.
Layout mnemonic
S-S-W-W-S-W
- Space
- Sunlight
- Weight
- Water
- Shade
- Wind
5. Structural Safety — Important Example
In the textbook case:
- Roof area = 4 m × 3 m = 12 m²
- Safe load = 150 kg/m²
- Total permissible load = 12 × 150 = 1,800 kg
- Estimated garden load = 1,200 kg
Therefore, the estimated load was within the stated safe limit. The students also waterproofed the roof and used bamboo supports for climbers.
Formula
Permissible total load = Roof area × Safe load per m²
6. Selection of Materials
| Material | Key point |
|---|---|
| Terracotta pots | Allow air/moisture movement |
| Plastic pots | Lightweight |
| Grow bags | Flexible and easy to move |
| Cement pots | Heavy; retain heat |
| Wooden containers | Allow air movement |
| Recycled containers | Old buckets/sinks can be reused |
| Potting mixture | Soil + compost + cocopeat/perlite/vermiculite |
| Watering equipment | Watering cans, sprinklers, hose pipes |
| Shade/support | Shade nets, bamboo screens, lightweight trellises |
Safety
- Heavy containers should be positioned safely.
- Distribute weight across the roof.
- Use trays/saucers under pots.
- Wear gloves while handling soil and organic matter.
7. Important Tools
| Tool | Main use |
|---|---|
| Hand trowel | Digging, sowing, transplanting |
| Pruning scissors | Cutting stems/dried leaves |
| Watering can/spray bottle | Gentle watering |
| Buckets/trays | Carrying soil and collecting drainage water |
| Pots/grow bags/nursery trays | Growing plants/seedlings |
Safety: Store sharp tools safely and avoid overloading buckets.
8. Bill of Materials (BoM)
A Bill of Materials helps to:
- Estimate cost in advance.
- Avoid unnecessary purchases and wastage.
- Organise work.
- Estimate labour cost.
Labour cost
Labour cost = Time × Hourly estimate × Frequency
9. Potting Mixture
For rooftop gardening, the growing medium should be:
- Lightweight
- Nutrient-rich
- Well-aerated
- Well-drained
Recommended proportion
Cocopeat/vermiculite/perlite : Compost/vermicompost : Soil = 1 : 1 : 1
Why not use only ordinary soil?
Ordinary soil is:
- Dense
- Heavy
- Prone to becoming compacted
- Poor for drainage when packed
This can reduce air reaching roots, cause waterlogging and lead to root rot.
A good potting mix remains loose and allows:
air + drainage + healthy root growth, while reducing roof load.
pH
Target pH of potting mixture: 6.5–7.0
- Below 6.0 → acidic → add garden lime.
- Above 8.5 → alkaline → add sulphur or organic manure.
- Test again after amendment.
10. Seed Germination Test
Procedure
- Count the seeds.
- Plant them in a tray/pot/container.
- Water regularly.
- After 2–3 weeks, count germinated seeds.
- Compare with total seeds planted.
- Calculate germination percentage.
- Compare with the seed-packet claim, if available.
- Healthy seedlings can be transplanted carefully.
Formula
Germination % = (Number of germinated seeds ÷ Total seeds planted) × 100
11. Irrigation
Too little water
Causes water stress → plants do not grow properly.
Too much water
Can cause root suffocation and waterlogging.
Pots require careful irrigation because roots cannot access deep soil and excess water cannot behave as it does in open ground.
12. Water Holding Capacity (WHC)
WHC = maximum amount of water that the growing medium can hold.
Procedure
- Take 500 g potting mixture.
- Record dry weight of pot + mixture.
- Slowly add water until saturated.
- Allow excess water to drain for about 10–15 minutes.
- Record wet weight.
- Calculate WHC.
Formula
WHC (%) = [(Wet weight − Dry weight) ÷ Dry weight] × 100
Example
If:
- Dry weight = 105
- Wet weight = 130
WHC = about 24%.
Water requirement example
If:
- Potting mix = 400 kg
- WHC = 25%
Approximate water requirement =
400 × 25/100 = 100 L
This is an approximate maximum requirement, not necessarily the amount to use every day.
13. Pest & Disease Management
You cannot completely eliminate pests and diseases because they are part of the ecosystem. The aim is to limit crop damage.
Integrated management includes:
- Physical — remove diseased leaves/larvae.
- Chemical — e.g. organic pesticide sprays.
- Biological — use/rear beneficial insects.
Regular observation helps identify symptoms early.
Important examples
| Symptom | Pest | Remedy |
|---|---|---|
| Chewed leaves | Caterpillar | Neem spray/turmeric |
| Discoloured leaves | Spider mites | Spray water |
| Deformed leaves | Aphids | Neem/chilli-garlic spray; early manual removal |
| Large holes/shiny trails | Slug/snail | Manual removal/salt lines |
| Wilted & chewed leaves | Chafers | Expose larvae, neem spray, hand-pick beetles |
| Black mould/weak sticky leaves | Whitefly | Neem spray/soap-water spray |
14. Weed Management
Weeds = unwanted plants growing in the garden.
Methods
- Hand weeding
- Mechanical/power weeders
- Mulching
- Chemical weedicides
Manual weeding
Identify → loosen soil → hold at base → pull slowly with root → level soil
15. Harvesting
Timely harvesting improves:
- Quality
- Freshness
- Shelf life
Delayed harvesting may cause over-ripening, taste loss and faster spoilage.
Four key rules
Gentle handling + Right time + Correct tools + Correct maturity stage
- Harvest preferably in early morning or late evening.
- Use scissors/pruning shears/small knives where suitable.
- Avoid pulling produce in a way that damages the plant.
- Harvest according to crop maturity.
Examples
- Spinach → tender leaves
- Tomato → red
- Coriander → before flowering
16. Storage
Basic rules
- Wash vegetables/herbs gently.
- Dry before storing.
- Use ventilated/perforated containers.
- Store according to crop requirements.
Important examples
- Spinach/coriander → cool, moist conditions.
- Tomatoes → room temperature until fully ripe.
- Herbs → stems in water or loosely wrapped in damp paper towel.
17. Harvest Time — Quick Revision Table
| Crop | Approx. harvest |
|---|---|
| Lettuce | 45–55 days |
| Spinach | 30–60 days |
| Radish | 25–45 days |
| Okra | 45–55 days |
| Capsicum | 60–80 days |
| Basil/mint/coriander | 25–30 days |
| Tomato | 55–70 days |
| Brinjal | 60–70 days |
18. Packaging
Leafy vegetables
Wrap in clean damp cloth/newspaper and refrigerate soon.
Tomatoes & chillies
Use:
- Baskets
- Trays
- Ventilated cardboard boxes
Avoid tightly sealed plastic bags because trapped moisture can cause rotting.
Herbs
Tie small bunches using jute string/paper bands and label them.
Flowers
Use baskets lined with damp cloth/corrugated sheets.
Memorise these:
- Sunlight: 5–6 hours/day
- Plant life cycle for project: 2–3 months
- Potting mix: 1 : 1 : 1
- Target pH: 6.5–7.0
- Acidic (<6.0): garden lime
- Alkaline (>8.5): sulphur/organic manure
- Germination test: 2–3 weeks
- WHC:
(Wet − Dry) / Dry × 100 - WHC example: 400 kg × 25% = 100 L
- WHC test drainage: 10–15 min
- Harvest: preferably morning/evening
- Main layout factors: space, sunlight, weight/safety, water, shade, wind
- Main pest-management approaches: physical, chemical, biological
- Weed: unwanted plant