Grafted mangoes on the roof: how to grow them and why

Climb onto the roof of a five-storey city house on a summer afternoon and you may well find this: a waist-high mango tree in a faded plastic drum, a few ripe mangoes hanging from its branches. Below is the din of the street, all around are concrete walls, yet up here is a small garden. Short of ground, city households are turning to their roofs, and the mango, the country's best-loved fruit, has found a place there too. The trick that makes it possible is the grafted sapling. Growing mangoes on a roof from grafted saplings takes little effort, works well and is kind to the environment. With sound planning and regular care, a roof can yield fresh, nutritious and delicious mangoes.

The mango is more than a fruit in Bangladesh; it is part of how people feel about home. In November 2010 the cabinet declared the mango tree the national tree. It is a big crop, too. Department of Agricultural Extension (DAE) figures published in the press show that in the 2023-24 financial year mangoes were grown on about 250,000 hectares and output reached about 2.589 million tonnes.

For city people, though, a mango usually means fruit bought at a market, with no idea where it came from or how it was grown. A tree planted by one's own hand closes that gap. The government is encouraging rooftop gardens as well. The Business Standard reported that in 2023 the local government minister announced that building owners in all city corporations and municipalities would get a 10 per cent rebate on holding tax for rooftop gardening. Both Dhaka city corporations had earlier offered similar rebates of their own.

To understand grafting, start with the seed. A tree grown from a mango stone may or may not resemble its parent; its fruit may be small, its taste different, and it takes many years to bear. In grafting, a shoot of the chosen variety is joined onto the stem of a sturdy young rootstock. Once the joint heals, the top of the plant carries exactly the traits of that variety. An Amrapali graft gives Amrapali; a Langra graft gives Langra.

That is why grafted saplings are ideal for a rooftop garden. They establish without much trouble and fruit quickly. They bear more than trees grown from seed. And grafted trees usually stay relatively small and bushy, which suits a pot and a small space. When buying, look closely at the graft joint: a smooth, firm union shows the graft has taken. Government horticulture centres or a trusted nursery are the safest sources.

Having the materials to hand before starting makes planting day smoother. For one mango tree you will need roughly:

• A large pot, half-drum or drum 18 to 24 inches deep, with several holes in the base.
• Pieces of broken clay pot or brick to cover the holes.
• Loam, rotted cow dung or compost, and sand, in roughly six, two and two parts.
• A little TSP and potash fertiliser.
• A healthy grafted sapling of a good variety such as Amrapali, Himsagar or Langra.
• A straight stake and soft string to tie the sapling.
• A few bricks to raise the drum slightly off the roof.

Mango trees love sun. Choose a part of the roof that gets plenty of direct sunlight for most of the day. In the shadow of a taller building or a water tank, the tree grows leggy and produces fewer flowers and fruit.

The second condition is drainage. Do not set a drum where rainwater pools on the roof, and make sure water draining from the drum runs quickly to the outlet. A large drum full of soil and water is heavy, so on an old or weak roof it is wise to be sure of the building's load-bearing capacity before installing many drums. Many gardeners line their drums up near walls or columns. Rather than setting a drum straight on the roof floor, raising it slightly on a brick at each corner lets air move underneath, stops water pooling and damaging the roof, and keeps the drainage holes clear. A waterproof coating on the roof adds another layer of safety.

Mango roots want to go deep, so the tree will not last in a small pot. Use a large pot or drum that holds plenty of soil, ideally 18 to 24 inches deep and about as wide. Cutting a plastic or metal drum in half to make two half-drums keeps the cost down.

There must be holes in the base so excess water can drain. Mango roots cannot tolerate standing water; starved of air, they rot, and the tree slowly yellows and dies. Pieces of broken clay pot or brick over the holes keep the soil in while letting the water out.

A potted tree cannot send its roots out in all directions in search of food as a field tree can; the soil in the drum is its entire larder. So the mix deserves care: 60 per cent loam, 20 per cent organic manure, meaning well-rotted cow dung or compost, and 20 per cent sand.

Loam is a balanced blend of sand, silt and clay; it holds water yet lets the surplus drain away. Organic manure keeps the soil crumbly and feeds the tree slowly. Sand stops the mix from caking, so the roots can spread and the water has a way out.

A little TSP and potash should also go into the mix. TSP supplies phosphorus, which helps roots develop; potash strengthens the tree against disease and improves fruit quality. Fill the drum with the mix and water it for a few days before planting, so the fertiliser settles into the soil.

Choosing the variety is a key decision. Buy good grafted saplings of varieties such as Amrapali, Himsagar or Langra. Amrapali is especially popular for pots. The Bangladesh Agricultural Research Institute (BARI) released it as BARI Aam-3. According to the Agricultural Information Service, it fruits regularly every year, the tree is relatively short and upright, and its flesh is deep orange and fibreless. That is why it is the variety most often seen in rooftop and balcony pots.

Himsagar and Langra are prized for flavour. Chapainawabganj's Khirshapat, also known as Himsagar, became Bangladesh's third geographical indication (GI) product in 2019, after Jamdani and hilsa. A GI is formal recognition that a product's identity is tied to a particular place. These varieties usually grow into bigger trees than Amrapali, so in a drum they need regular pruning to keep their size in check.

Once the drum is ready, dig a hole in the centre the size of the sapling's root ball. Cut away the nursery bag carefully so the soil around the roots stays intact. Set the base of the sapling firmly in the soil and press the soil around it by hand so no air pockets remain.

Make sure the graft joint is not buried. Water lightly straight after planting; too much water can make the loose soil slump and tip the sapling over. Roofs are windy, so for the first few months it helps to tie the sapling loosely to a straight stake.

Water is the rooftop tree's biggest test. A concrete roof bakes at midday, and the limited soil in a drum dries far faster than a field. Keep the soil moist at all times, but never let it become waterlogged. As a rule, water daily in summer and every two or three days in winter.

Testing the soil with a finger before watering is a good habit. If the top inch or two feels dry, water; if it is damp, wait another day. Morning or late afternoon is the best time; water poured on hot soil at midday evaporates quickly. The monsoon brings the opposite problem: check that water is not pooling in the drum and that the drainage holes are not blocked.

Once the tree is big enough to fruit, the watering routine shifts a little. An Agricultural Information Service article on orchard care says it is best not to irrigate for a month before flowering, because watering then pushes out new leaves and reduces the number of flower clusters. After fruit set, regular watering until the monsoon helps reduce the drop of young fruit. Because the soil in a pot dries fast, in the weeks before flowering the amount of water can be reduced while taking care the tree does not wilt.

The nutrients in a drum run out over time, so regular feeding matters. Apply organic manure every month, starting a month after planting. Rotted cow dung, compost or water in which mustard oilcake has been left to rot are good organic foods for a potted tree. Work it lightly into the soil a little away from the trunk, towards the rim of the drum, then water.

Potash at flowering improves the crop. It helps the tree hold on to its flowers and young fruit and improves the sweetness and colour of the mangoes. Chemical fertiliser should always be used sparingly; too much in a drum's limited soil can burn the roots. If in doubt about doses, ask the upazila agriculture office or the nearest horticulture centre.

Once the tree is grown and fruiting regularly, it helps to know the schedule used in field orchards. The Agricultural Information Service advises applying the full amount of cow dung, TSP, gypsum, zinc sulphate and boric acid, plus half the urea and half the MOP, from mid to late September, with quantities rising as the tree ages. A drum-grown tree needs far smaller amounts than an orchard tree, but the timing still applies: well fed at the end of the rains, the tree firms up before winter and flowers better the next season.

Pruning keeps a potted mango shapely and fruitful. Cut out dry branches and dead leaves regularly. Thinning crowded shoots in the centre lets light and air into the canopy and cuts disease. The Agricultural Information Service advises cutting out diseased or dead branches, with a little healthy wood, after the harvest, because new shoots appear once the fruit is picked, and it is on those shoots that next year's blossom forms.

Act quickly if disease appears. Black spots on the leaves, blossom that blackens and falls, or marks on young fruit may be signs of anthracnose, a fungal disease. Because a rooftop tree is always close at hand, a daily look at its leaves, branches and blossom catches problems early.

Family members walk on the roof and children play there, so organic methods should come before chemicals. Organic pesticides such as neem extract can be used as needed, and pheromone traps reduce pest attacks. A pheromone trap holds a chemical that mimics the insect's own scent; males are lured in and caught. Such traps work well against the fruit fly, one of the mango's worst enemies.

At blossom time, hoppers, sap-sucking insects, drain the flower clusters and make them drop. The Agricultural Information Service says spraying insecticide thoroughly over the whole tree some 15 to 20 days before the blossom emerges brings the pest under control early. For heavy attacks, the Agricultural Information Service advises spraying a cypermethrin-group insecticide at 1 millilitre per litre of water when the blossom is 10 to 25 centimetres long but before the flowers open; spraying during full bloom harms bees and other helpful insects. Once the young fruit starts to swell, fruit bagging, wrapping each mango in a special paper bag, is described by the Agricultural Information Service as the most effective and profitable protection against fruit flies and mango weevils. On a rooftop with a handful of trees it can be done by hand.

The great advantage of a grafted sapling is a shorter wait: grafted trees usually fruit within two to three years. A young tree may flower early, but letting it carry every fruit weakens it, so until the tree is strong enough it is wise to keep only a few.

Pick the fruit with care once it ripens. When the skin near the stalk begins to turn slightly yellow, or half-ripe fruit starts to drop on its own, it is time. Cut the mango with its stalk rather than pulling it off; that keeps the sap from staining the skin, and the fruit lasts longer.

Laid out in a single layer in the shade on newspaper or straw, picked mangoes ripen evenly on their own within a few days. Piled on top of each other, they bruise where they press together and spoil faster. Instead of stripping the tree at once, picking the fruit as each one matures gives a steady supply of fresh mangoes through the season, which is the real difference between your own tree and the market.

The first reward is fresh, pesticide-free fruit. Mangoes from your own garden are natural, because you know exactly what fertiliser and sprays went on them, and there is no worry about chemical ripening agents. That makes them healthier than market fruit. Mangoes are nutritious too: according to the US Department of Agriculture's food database, 100 grams of ripe mango holds about 60 calories and about 36 milligrams of vitamin C, along with the building blocks of vitamin A.

The second reward is good use of space. Even a small city home can grow mangoes on the roof, and the tree makes the roof more attractive. The third is money saved. Picking fruit from your own tree costs less than buying it, and a tree once planted bears for years, so over time it pays its way. The holding tax rebate for rooftop gardens adds to the sum.

The fourth reward is environmental. With trees on the roof, the sun does not beat straight onto the concrete, so the roof and the rooms below stay cooler. Trees trap dust and help keep the air around the house cooler and cleaner. Birds and butterflies return to the concrete city.

The fifth is for the mind. Gardening eases stress. A few minutes tending a tree after work, watching new leaves unfurl, waiting for the first blossom: all of it brings a kind of calm. It is a fine hobby that keeps body and mind healthy, and children learn first-hand how a tree grows and where fruit comes from.

Growing grafted mangoes on a roof takes little effort and does a great deal for the environment and for health. A sunny spot, a good drum, carefully made soil, a sound graft and regular water and feeding are all it takes to harvest delicious, nutritious, pesticide-free mangoes. The start of the rains, the months of Jyaishtha and Ashar, is a good time to plant, so the planning can begin now.

A drum takes up very little of a city roof. But the pleasure, a few years on, of picking the first ripe mango from your own tree on a summer afternoon is something no market fruit can match.

Photo: A mango seedling in a pot, SYFTV1 / Wikimedia Commons (CC0)