The flowers are grown on pockets fixed on the concrete pillars, which also allow water to drain down into the highway drainage system.
Transport Cabinet Secretary James Macharia said the technology used is called geo-flower and the plants are not artificial as could be perceived.
Statistics show every km of 27km stretch cost about Sh3.6bn, dwarfing the 50km Thika superhighway, which was completed in 2012 and built at a cost of Sh32bn at Sh640 million per km.
"We felt that the travel should not be boring. The covering of columns with plants gives it a soft architecture on the walls and brings relaxed feeling when travelling. It is also part and parcel of conserving the environment as the plants on the pillars will absorb carbon emitted from the vehicles using the expressway," said Odenyo.
"They will be part and parcel of the environment that we find ourselves in. It is important to ensure trees are retained because of the contributions they make on climate change, "she added.
Photos by Stafford Ondego.