Ornamental Horticulture

Plants for highways

The roadside trees on the national highways should not only provide shade but preferably also have some economic value. With this in view many of the highways have been planted with trees such as tamarind, mango, Eugenia operculata (Syn. Syzygium operculatum), etc.

Neem (Azadirachta indica ; Syn. Melia azadirachta), Mahua (Madhuca indica; Syn. Bassia latifolia), Dalbergis sissoo (Indian rosewood), and Shorea robusta are roadside trees of economic value.

The highway trees should never be planted in mixed avenues, but only one species should be planted for a long distance of the road. For example, if neem trees are planted in pure avenue for a long stretch, an oil extracting industry can be started on the roadside. Similarly, Sal yields valuable timber and its seeds yield an edible oil which is used as an ingredient in the manufacture of chocolates and other purposes. If a single species is planted in a pure avenue for miles together this looks more beautiful and gives a wavy appearance to the skyline. In such a case the management and gap-filling also become easier.

The trees should be planted 12 m apart in the row and at least 5-6 m away from the edge of the roads, so that they get enough space for spreading and do not interfere with the traffic. If a road is as wide as 30 m or more, double rows of trees should be planted, rows being spaced 10-12 m apart. The inner row may be of a flowering tree. If a roadside tree is intended for timber, replacements should be planted well ahead (4-6 years) of the cutting time.

The selection of trees for a particular locality is done giving due consideration to subsoil water, soil climate including rainfall, locality etc. As for example, if Mahua is planted along a highway near the tribal belts of Madhya Pradesh or Bihar, the flowers can be marketed easily as these are in great demand among the tribals. Trees with shallow root system such as Millingtonia hortensis and brittle wood as in the case of Eugenia jambolana, Albizzia lebbek, Cassia siamea and Eucalyptus should never be planted on highways, as during storms they get uprooted or branches are broken and casualties may result on the unaware roadusers. Neem and tamarind can grow very well in dry localities. Samanea saman (Syn. Pithecolobium saman) and Dalbergia sissoo grow better in places having a rainfall of 100 cm or above. Often the banyan (Ficus benghalensis) is planted on highways, which is not appropriate as its growth is unwidely. However, banyans can be planted singly and a little away from the road at some distances, for its cool shade. Similarly, Ficus religiosa is also not a very good roadside tree. On the other hand, Albizzia procera is a good roadside tree. Polyalthia longifolia, though not a tree of great economic value, is a very good shade tree and thus suitable for roadside planting. Thorny trees should not be planted along roadside as the falling thorns may damage the tyres of vehicles. Though not planted on our highways, shrubbery borders with suitable shrubs can be maintained along the highways. This will improve the scenery.

"Mixed plantation" consists of planting different varieties of trees in a mixed avenue against the planting of a single species. This has got a couple of advantages. The first is that the different plants flower and fruit at various seasons thus enhancing the aesthetic view for a longer time of the year. The other advantage is that this planting avoids monotony.

The other method is "group planting" where a group of 3-4 trees or more are planted at specified intervals instead of planting in avenue.

Informal planting method, which consists of planting informally without following any regular pattern is suggested for rural areas.