Rooftop gardening has become a popular agricultural practice in Bangladesh. It refers to growing flowers, fruits, and vegetables scientifically on unused rooftops or balconies of buildings. In English, this practice is known as rooftop gardening. Currently, rooftop gardening has gained considerable popularity in Dhaka and other cities across the country. Looking at the rooftops of most buildings, it is common to see gardens containing a variety of plants. However, many of these gardens have been established without proper planning. With a well-planned approach, it is possible to grow almost any type of plant, including vegetables, on a rooftop.

The importance of rooftop gardening is increasing worldwide. In urban areas, rooftop gardens for growing flowers, fruits, and vegetables are no longer merely a hobby. They can serve as a source of economic benefits while also helping protect the environment and improve air quality.

In Singapore, roadside footpaths are being covered with green grass. In 2001, the Tokyo Metropolitan Government passed a law requiring gardens to be established on at least 20% of the rooftop area of new buildings. As a result, Tokyo's average temperature reportedly decreased by 1.5 degrees Fahrenheit. Research has shown that rooftops account for approximately 25% of a building's total area, much of which generally remains unused. Establishing rooftop gardens allows this space to be used effectively while also providing financial benefits.

Currently, approximately 50 million people live in urban areas in Bangladesh. By 2025, this figure was projected to reach approximately 85 million, representing 50% of the population, and by 2050, it was projected to reach 270 million, or 100% of the population. Rapid population growth, climate change, declining agricultural land, and the continuous deterioration of agricultural biodiversity have been identified as major obstacles to ensuring adequate food production and supply. To meet the growing food demands of the population, vegetable production can be increased through extensive gardening on rooftops, in home gardens, and in other unused spaces, helping fulfill people's nutritional needs.

Planning for a Rooftop Garden

When establishing a rooftop garden, proper planning is essential to prevent damage to the roof. Plants should be positioned near the roof beams or columns. Measures should also be taken to prevent dampness and moisture accumulation on the roof.

Placing drums or pots on rings or bricks allows air and light to circulate underneath them, helping protect the roof from dampness. A suitable net-finish layer can also help protect the roof against moisture.

Generally, loamy and sandy loam soils are suitable for growing healthy plants.

Garden Design

First, prepare a layout that defines the boundaries and dimensions of the rooftop. Leave some open space and pathways in the middle to ensure convenient movement. If the rooftop is particularly large, divide it into several sections and provide pathways approximately 1–1.5 meters wide between them.

Along the rooftop railing, a raised, concrete trough-like structure can be constructed, leaving a gap or elevation of approximately 15 centimeters above the roof surface.

The design should also include a trellis structure in one corner of the rooftop or beside the rooftop stairwell, supported by iron pipes or wooden posts. Designate separate areas for different types of plants, identify suitable locations for containers and planting structures, and mark the location of the water source.

A service area or small storage room should be included in the layout for storing gardening tools and equipment. To improve the garden's appearance, consider the size, shape, and color of the plants.

Fruit trees should preferably be positioned toward the middle of the rooftop rather than along its edges. If climbing plants are to be grown along the rooftop boundary, install a low trellis above the railing or attach iron clamps or hooks to the inside or outside of the railing.

For climbing plants such as yardlong beans, bitter gourd, passion fruit, and grapes, wooden or bamboo poles can be inserted into these hooks. GI wires can then be stretched along the poles to create vertical trellises or support structures.

An open area can be converted into a lawn by laying sheets of green grass. If you wish to create a water garden using water-filled pots or containers, designate a suitable location for the water troughs or aquatic planters.

Essential Materials and Techniques for Rooftop Gardening

Containers

Various types of containers can be used for rooftop gardening, including flowerpots, half drums, concrete troughs, permanent raised beds, and multilayer grow bags for vegetable cultivation, commonly known as bag gardening.

Soil

Soil is an important factor in rooftop gardening. A soil layer approximately 15–20 centimeters deep is sufficient for leafy vegetables and shallow-rooted flowering plants. However, medium-sized plants and those with larger root systems require a soil depth of at least 50 centimeters.

Loamy soil is generally the most suitable option. For leafy vegetables and ornamental foliage plants, a mixture containing equal proportions of organic manure and soil is beneficial.

Planting Seedlings in Containers

Follow these steps when preparing a half drum for planting:

1. Make five or six drainage holes, each approximately 1 inch in diameter, at the bottom of the half drum to allow excess water to drain. 2. Place broken pieces of clay pots over the drainage holes. 3. Spread a layer of brick chips approximately 1 inch thick across the bottom of the drum, then cover it with sand. 4. Fill approximately two-thirds of the drum with a mixture of equal proportions of loamy soil and well-decomposed cow dung. 5. Add approximately 50–100 grams of mixed fertilizer per half drum and mix it thoroughly with the soil. 6. Fill the remaining space with soil and allow the prepared drum to stand for 15 days. 7. After 15 days, make a hole in the center of the drum, large enough to accommodate the root ball of the selected plant, and plant the seedling. 8. Trim any excessive or dead roots while ensuring that the root ball remains intact. 9. Secure the newly planted seedling to a supporting stake. 10. Water the base of the plant thoroughly after planting.

Replacing Soil in Containers

Although replacing the soil every year may not be necessary, it is advisable to replace the old soil in pots approximately once every two years with fresh soil mixed with cow dung manure.

During this process, take care not to damage the plant excessively. As far as possible, remove some of the old soil around the roots and add fresh soil mixed with suitable fertilizer.

Fertilizer Application Guidelines for Rooftop Gardens

If plants do not receive adequate nutrients, their growth and productivity decline, and they become more susceptible to pests and diseases.

Water used to wash fish, meat, and vegetables can provide plants with some additional nutrients. In addition, mixed fertilizers and bone meal can be applied occasionally, while micronutrients such as zinc, boron, magnesium, and manganese may be applied once a year when needed.

Fish bones, small pieces of animal bones, eggshells, discarded vegetable parts, and leaves can be decomposed in a drum and used as organic fertilizer in rooftop gardens. These materials can help improve plant growth when properly composted.

For rooftop plants that have been growing for several years, carefully removing some of the soil around the base and replacing it with fresh potting media can help restore plant health.

Where feasible, plants can also be pruned and carefully lifted with some of their root soil intact so that the growing medium can be replaced with fresh, fertilizer-enriched soil. Transferring plants from smaller pots to larger ones can also help improve their growth and overall health when repotting is appropriate.

Some gardeners use micronutrient and plant-growth products, such as Silvamix, Litosen, and Flora, to help reduce flower and fruit drop and improve fruit production.

Monthly Fertilizer Application Schedule

The month can be divided into three periods, allowing fertilizer to be applied three times per month.

First application

Mix the following ingredients thoroughly in 1 liter of water:

  • 1 teaspoon of urea
  • 1 teaspoon of triple superphosphate (TSP)
  • 1 teaspoon of potash fertilizer
  • ¼ teaspoon of boron fertilizer

It is preferable to soak the TSP fertilizer in water for 3–4 hours beforehand.

For seedlings or small plants growing in pots, the solution can be applied around the base of 4–5 plants. For larger plants in large pots, it can be applied to two plants, while one plant can be treated when growing in a half drum.

Second application (10 days after the first application)

Mix the following ingredients in 1 liter of water:

  • 1 teaspoon of urea
  • ¼ teaspoon of zinc fertilizer

Apply the solution around the base of 4–5 small potted plants, two plants in large pots, or one plant in a half drum.

Third application (10 days after the second application)

Mix the following ingredients in 1 liter of water:

  • 1 teaspoon of urea
  • ¼ teaspoon of sulfur fertilizer

Apply the solution around the base of 4–5 small potted plants, two plants in large pots, or one plant in a half drum.

This cycle can then be repeated each month.

For the second and third applications, foliar spraying may also be considered where appropriate. Apply fertilizer solutions in the late afternoon, when temperatures are lower. Water the soil around the plant sufficiently so that it becomes moist but dries by the following day.

During the rainy season, adjust fertilizer and water applications according to the weather and soil conditions. Avoid allowing excess water to accumulate around the roots, as this can damage plants.

In conclusion, follow the recommended fertilizer schedule to achieve the desired yield.

Pest and Disease Management

Environmentally friendly Integrated Pest Management (IPM) practices should be followed to control pests and diseases in rooftop gardens.

Avoid chemical pesticides unless absolutely necessary. Instead, biological or botanical pest-control products, such as Nimbecidine and Bikao-1, may be used where appropriate.

Mealybugs may attack guava, jujube, lemon, mango, karonda, olive, eggplant, and other plants. When these pests infest a plant, white, cotton-like masses may appear on the undersides of leaves. These insects cannot fly. Infested plants may become weak, their leaves may turn reddish, leaves and fruits may fall prematurely, and fruit shapes may become distorted.

Whiteflies may also attack plants such as guava, lemon, olive, and eggplant.

The following measures can help manage these pests:

1. Handpicking: Remove visible pests manually whenever practical. 2. Biological pest control: If necessary, apply a suitable biological pest-control product, such as Bikao, according to its label instructions. 3. Soapy water: A solution containing 3–4 grams of detergent powder per liter of water may be sprayed on the undersides of leaves. However, household detergents can damage plant foliage, so a labeled insecticidal soap is preferable. Test any spray on a small portion of the plant first. 4. Garden maintenance: Keep the rooftop garden clean and prune plants appropriately to reduce the likelihood of pest infestations and diseases.

Regular monitoring, proper sanitation, and timely intervention can help maintain healthy plants while reducing dependence on chemical pesticides.

Note: The fertilizer quantities, application intervals, and population projections above have been translated from the original Bengali text and have not been independently verified. Fertilizer requirements vary by plant species, container size, soil conditions, and product formulation. Check the relevant product label or consult a local agricultural expert before applying fertilizers or pesticides.