The carpet of leaves that covers tree-lined avenues in neighbourhoods like Whitefield, Fraser Town and Jayanagar, to name a few, is a familiar sight. This is part of an annual ritual — shedding of leaves — that peaks in the months of February and March. The discarded leaves are a rich source of compost or mulch and organic manure, but for the most part, are treated like garbage: swept into piles and often burned.
Horticulture expert Dr. S. V. Hittal Mani says, “Bengaluru is left with a 50,000 tonnes of dry leaves every year from its estimated 10 lakh trees. There is potential to create 10,000 tonnes of leaf-manure compost, which can be the best soil enhancers to help the community of farmers in the suburbs. But not even a tenth of it is being made available now, as most of the dry leaves are being burnt or simply relegated as garbage by the BBMP and other local institutions. This is an approximation in the absence of official data regarding tree count.”
Well-known horticulture experts at the University of Agricultural Sciences, the Indian Institute of Horticultural Research, Lalbagh and Cubbon Park that has Dr. Mani in the advisory committee, and tree experts have estimated that there are more then 50 different species of avenue trees in Bengaluru.
According to S. B. Bommanahalli, Director of Horticulture, with the exception of a few big parks and institutions, there is no system to convert these leaves into manure. It’s one of the reasons why some people burn them.
BBMP officials admit that while burning of leaves is banned, the ban is hard to enforce.
Only three shredders
IISc.’s comprehensive solid waste management plan, which aims to make the institute a zero discharge campus, did have a provision for management of dry leaves. However, by consensus it was decided to let the leaves naturally compost within the large campus.
While some big institutions and parks are directly handling dry leaves in an eco-friendly manner, the civic body is in charge of collecting dry leaves from roads and public places.
But given the volume of leaves that are shed every year, the BBMP has just three shredders: one each in Byrasandra, Pattabhiramanagar and Basavanagudi wards. There is a proposal to put up a leaf litter compost unit in every ward and ensure that there is leaf shredder for every three wards. “A leaf shredder costs around Rs. 4 lakh. It will help shred leaves into a fine powder to speed up the composting process. However, this plan is still in the initial stages and is unlikely to be implemented before the end of this summer,” the official added.
Several top horticulturists believe that a legislation to preserve dry plant waste will bring more accountability to local bodies and institutions.
Worth their weight in manure
The tree cover varies with each neighbourhood. “Each area has a different kind of tree cover. But, on an average, the city has around 5,000 trees per sq km,” says Dr. Mani. “Each tree sheds about 50 kg of dry leaves a year. So we get a total of 50,000 tonnes. The potential for conversion into manure is massive, but where is everything going?”
‘Get local leaf composters’
Jaya Dhindaw, a researcher formerly with the Indian Institute of Science, says local, low-cost leaf composters can be adopted at the community level to deal with the large number of leaves that litter the city during the dry seasons. “These machines cost just around Rs. 12,000 and do not require any power. They can give enough manure to cater to the demand of parks in the area,” she said. Even twigs and small branches that fall off during the rains can be reduced to mulch in wood-chippers and used as manure.