Khus ki Tatti: there, it is now down in black and white - no need to cringe at the words anymore. Throughout childhood, this seemed to pertain to a fecal matter of some creature called Khus, for in Urdu the phrase lends itself to this confusion. We children shook with giggles as adults of refinement spoke of it in all seriousness at the dinner table. But now, as we go hunting for it in vain in Lahore, we know that it means the woven mats of a tropical grass called Khus. The rest of the world knows this alluring grass as vetiver.

By the way, taat means a woven fibre mat in Urdu, and tatti is its diminutive form. But the latter word does have another, more base meaning, namely excrement.

Our alluring grass is Vetiver zinzanoides that is native to the Asian subcontinent, although other varieties also appear in Southeast Asia and Southern Africa. The word vetiver is French but originates from the Tamil ver that means root.

My Uncle, who left the country to live in the UK half a century ago, recalls the use of this grass with vivid clarity in our family’s pre-Partition home in Roorki, India.

“In the dry months of summer, Roorki would receive a loo (apologies for another base word, but this means a hot, dry wind that is peculiar to northern India). And in our home, we had a windowless room like a taikhana or basement. In the mid-day, the children would be accommodated for an afternoon rest or kehlula in this dark room, whose open door-frame was covered with a wet Khus ki tatti. This kept us cool as the hot wind blew outside, emitting a distinctive perfume never to be forgotten.”

The soothing, calming properties of vetiver are widely known as its aromatic oil helps alleviate anger, irritability and stress. It is notable for relief from physical and mental exhaustion.

An ancient perfume of our region, the smell of khus is described as deep, sweet, woody, smoky, earthy, amber and balsam. We associate it with dry heat and muslin clothes when it is used as a unisex perfume during pre-monsoon summer. Since there is no synthetic substitute for this perfume, vetiver grass is traded widely and grown in various parts of the world.

While Haitian vetiver is considered the finest in French perfume industry, like a secret in plain sight, Indian khus is all consumed within the sub-continent itself. The finest among the khus oils is from northern India being harvested from the wild and not cultivated as in other places.

So the khus ki tatti my family used in Roorki was probably the high-grade, wild khus harvested from within the UP. But what is this cooling and aromatic grass?

Vetiver zinzanoides is related to lemongrass and citronella, being a tropical grass that grows up to 7 feet tall. Found wild in fresh-water wetlands, floodplains and on stream banks, it is tolerant of very poor soil conditions. For up to three months, the plant can be submersed in water and still survive, alternatively, for months it can be starved of water and come out green. It’s secret is the root system that may grow its woody strands up to 13 feet deep. And it is these amazing roots that make the grass famous. Once the roots are dug up, cleaned, and dried, they must be soaked and distilled into essential oil for perfume. For mats, the roots are cut and woven by binding them with ropes or cords.

Instead of hanging khus mats, we now use them as pads or panels in desert coolers in the dry summer heat. Because they are naturally tolerant of long immersion in water, the khus roots also contain their own chemicals to ward off rot and emit a delectable aroma.

Which gets us to the subject of evaporative cooling, a prominent usage of khus and its tattis.

Our desert coolers of Pakistan used khus in cooling pads to run water over them and emit cooled air through fans. Now, these are replaced with straw or wood shaving and sometimes corrugated cardboard too. Through this method, the temperature of dry air can be dropped significantly through the phase transition of liquid water to water vapor while evaporating. This can cool air using much less energy than refrigeration.

We estimate in our home that we spend about Rupees 4,200 over 7 weeks using our desert cooler in comparison to the prohibitive Rupees 45,000 if an air conditioner is used in the same way. A difference of some tenfold ensues, and our carbon footprint is probably much less then tenfold.

Although khus is no longer to be found in Lahore markets, it used to come from Bangladesh and is now unaffordable. Thought to be present in southern Punjab, Thatta, and Badin, its occurrence is unclear. Yet we owe to khus an appreciation for its evaporative cooling of our homes, even while we now use poor substitutes.

Just as trees transpire large amounts of water through pores in their leaves, and through this evaporative cooling, forests interact with climate at local and global scales, so too does the alluring khus grass inform us about how to control our footprint on this finite earth of ours – all the while cooling our anger and soothing our exhaustion.