Greenery is good, right? Well, not all kinds, apparently. While most plants and trees are good for the earth and for us, some are downright disastrous, while some others are borderline.
Obviously then, given the scant land space and water resources in cities, we can't afford to grow the wrong kind of greenery.
So then, which are the trees and plants that we can grow, and which are the ones we need to avoid?
On the fence
To begin with, consider two species commonly used for fencing or screening. The ashoka tree is a tall and royal looking species, but as in some humans, this suave external form conceals internal greed.
Ashoka trees drain groundwater and parch the land. The thorny velikatan plant does likewise. “Worse, velikatan alters the soil in such a way that no other species flourishes in the vicinity”, says Indrakumar, indigenous plant researcher and environment activist. “Velikatan's firewood generating characteristic is an advantage in rural areas, but it is certainly not desirable in urban settings,” observes Professor D. Narasimhan, Department of Botany, Madras Christian College.
Besides this, velikatan is an invasive species that usurps land resources and its thorns are infectious. What, then, is the alternative?
Try a bougainvillea hedgerow. Bougainvillea grows fast to form a thick green fence. You could also introduce trees like punnai and magizham to form a pillar of support for the bougainvillea, or have other creepers such as bluebells or manoranjitham (with its heady fragrance) trail in between the bougainvillea to create a riot of colour.
Besides offering a privacy screen, this green wall provides niches for bugs, beetles, small birds like sunbirds, and hooks for the useful spider to spin webs and keep the much-needed web of life going.
Then, there is the bamboo option. Tall bamboo reeds grown close together in a line form a classy looking natural screen. “Bamboo reeds are efficient carbon sinks and drought resistant too, and can survive on very little water”, informs Prof. Narasimhan.
Trees we need
“Avoid trees like gulmohar, the rain tree, and the copper pod trees. While the gulmohar's shallow roots make it vulnerable to be uprooted and struck down during cyclones, the city already has too many copper pod and rain trees. We need to preserve and promote plant diversity rather than keep growing the same kind of trees everywhere. Otherwise, these species will be wiped out”, says Prof. Narasimhan. Especially so, considering that cities are growing bigger and taking up more and more of countryside space. He recommends trees like the punnai (a hardy, coastal tree with fragrant flowers and attractive foliage), the medium sized mavalingam tree with edible fruits that sustains birdlife, the fragrant magizhampoo tree, and the vennagu or tada tree.
Log on to cfrmcc.yolasite.com where Prof. Narasimhan gives a comprehensive list of useful trees.
A word about the ubiquitous coconut trees. They do yield coconuts, but that apart, they don't do much. They don't offer much green cover, and their strong roots can attack building foundations. “In a hot city like Chennai, we need shady trees which can shield the ground and save the groundwater reserves from getting evaporated”, says ‘Poochi' Venkat, environment activist and macrophotographer.
So while planning a garden, try trees like mango, the umbrella tree, the Indian coral tree with nectar laden flowers, the huge red silk cotton tree, etc, whose broad canopy and leafy branches protect groundwater reserves and cool the space. Also recommended are smaller fruit yielding trees like guava and the lime tree to sustain birds and bees.
And, then, there are those plants that don't do active harm, but use up limited land and other resources that could have been used to raise more crucial plants.
So think, do you really need an exotic ornamental plant? How about ecologically effective and useful plants like the tulsi, a great oxygenerator.
For floral effect, try periwinkles, ixora, the fragrant night jasmine, nandiyavattai, rose, and hibiscus with its spectacularly coloured and nectar laden flowers that attracts birds and bees. If you want more variety try easy-to-grow cacti, and maybe a few water purifying plants like kalvazhai and seppankizhangu…
The watchword — go local, and promote endemic plant diversity. Exotic species are not just difficult to grow, they are also generally environmentally redundant. So, think, before you plant.
Try to keep out wrong greenery. One must have a clear idea as to what trees and plant one can grow.