Street-wise trees for roadsides, parking lots and highways

Life Landscapes, the landscaping division of Life Green Group has decided to take a closer look at the street trees that line our roadsides and parking lots.  Here are some things a facility manager or landscape architect should think about before a trees drips sap on the sunroof or starts pushing up the paving. 

Definition of a street tree:

A street tree is non-scientific landscaping lingo for vegetation that is ideally suited to growing along pavement, roadsides, driveways, highways and parking lots.   

Why street trees are important?

Johannesburg has a reputation for being one of the most tree’d cities in the world with all our boulevard botanicals.

Iconic boulevard botanicals

Trees are what make roads iconic. What would Hollywood Boulevard be without its  postcard perfect palms tainted with rose-tinted dreams? Lambard Street, San Francisco, would be non-existent without the influence of landscape architects and hydrangeas. Buenos Aires9 de Julio Avenue, the widest avenue in the world, is practically a park it is littered with so much vegetation. What would Paris be without its fairy lights and neat hedge work framing the Champs Elyees? You couldn’t call Pretoria the Jacaranda City without this be-loved purple flowering tree.  

pink

Science says plant street trees

Trees are particularly important in urban centres, not only do they provide much need softening greenery among the skyscrapers, trees control urban heat islands. All that concrete found in cities results in significant temperature spikes and trees are able to regulate temperature. Planting trees in roadside flowerbeds you can also reduce urban water runoff as way is absorbed into the ground. So does your hood have wood, because it should. 

street-trees-fight-urban-heat-island-effect

Temperature spikes in concrete jungles © Berkeley Lab

Hedges, highways and headlights

Most drivers will notice that South Africa’s highways are lined with hedges and there is a very good reason for this. Hedges stop headlights blinding drivers in on-coming traffic, offering an important roadside function. Should a vehicle get out of control, a hedge will not stop a car but it will slow down the momentum of the vehicle. So instead of using Oleander try these:

Some useful hedges for highways and road islands:

  • Lemon thorn (Cassinopsis ilicifolia) is fast growing and dense drowning out headlights effectively
  • Pride of De Kaap (Bauhinia galpinii) scrambling and evergreen makes ideal highway vegetation
  • Puzzle bush (Ehretia rigida) is adaptable and water-wise it is also common throughout ZA
  • Spekboom (Portulacaria afra) produces more oxygen than any other plant so why not convert the carbon from your car into oxygen along your journey. It is extremely hardy and readily propagated.

What makes a good street tree?

Let’s start at the roots; a good street tree does not have an invasive root system but rather a tap root. Invasive root systems will pull up infrastructure, break pipes and lift the roadworks whilst trying to create its own subway system. (So ficuses do not make for respectable roadside vegetation).

Working our way higher up the tree, a proper parking lot plant should not drop fruit. Fruit trees, especially berries, stains pavements and make for a rotting mess. Fruits are also eaten by frugivorous birds and then the bird faeces become a real pavement special to deal with. A superlative street tree will also not spit sap or nectar that could ruin a car’s paint job.

naturescaping trees

Example of a bad street tree © Bernard Dupont

Less crucial are the leaves, but evergreen trees make for neater street trees, rather than deciduous. Deciduous trees are great for autumn colour and mulch, but when they’re in flowerbeds. The leaf debris just builds up on pavements and in roadside drains, making for unnecessary landscape maintenance.

Street trees for roadsides, parking lots and highways

Life Landscapes also recommends trees that are water-wise and have flat or round crowns to give extra shade and attractive flowers are always aesthetically pleasing. In windy areas like Cape Town street trees need to be staked correctly to avoid being blown out of their branches.

6 Indigenous South African street trees

  • African Holly (ilex mitis) – is a real shade-giving specimen, with small fruit and a long flowering period from spring to summer. It reaches 30 metres.
  • Cape Chestnut (Calodendrum capense)– idyllic shade, stunning pink flowers, the cape chestnut makes for a beloved pavement special with its dense round crown.
  • Fever tree (Vachellia xanthophloea) – fever trees with their lime green bark make for a popular street tree. These trees, like all Vachellia species, do have slightly invasive root systems.
  • Indigenous palms - Ilala palm (Hyphaene coriacea), Pondoland coconut (Jubaeopsis caffra), Wild date palm (Phoenix reclinata) all give the Beverly Hills look and feel but in South Africa that is restricted to Durban.
  • Lucky bean trees (Erythrina lysistemon) – set the road alight with the burning flowers of the lucky bean tree. This deciduous tree is an extremely iconic street tree.
  • Wild peach (Kiggelaria africana) - no fruit, no nectar, no invasive root system, no falling leaves. The 20 metre tree makes for a street smart specimen.
good indigenous street trees

Cape Chestnut © Melburnian