Topsoil from Buckingham Palace could soon be growing marijuana as Tate Modern director Chris Dercon admitted visitors had already begun to "guerrilla garden" the new Turbine Hall exhibition.
Artist Abraham Cruzvillegas's Empty Lot features 240 wooden planters holding soil from 34 London parks and gardens - but visitors have begun throwing their own seeds onto the plots even before the sculpture officially opens.
Asked if visitors might throw the drug's seeds onto the soil, Curator Mark Godfrey said: "As to what grows - you mentioned marijuana - people might throw seeds in. We don't know."
Director Chris Dercon said that although throwing seeds will not be actively encouraged, the Tate has accepted that such plants might grow.
"We don't invite anyone to throw anything on it; it will happen. I already saw some people throwing seeds this morning. I don't know which kind," he said.
Cruzvillegas, however, said "the most optimistic and hopeful thing" that had happened so far was someone dropping an apple onto the planters.
The Queen's residence was one of the sites from which 23 tonnes of soil were collected - which also included The Barbican Estate, Peckham Rye, Kew Gardens and Spitalfields City Farm.
Exploring the idea of unpredictability and hope, Cruzvillegas planted nothing in the soil and visitors will be able to see what emerges and changes over the exhibition's six-month stay. Mushrooms and weeds have already begun to bloom in the planters.
Dotted around the structure are quirky lampposts built from skip-scavenged materials that fit with Cruzvillegas's theory of autoconstruccion, or "self-construction", based on how his parents' generation improvised with materials they could find to build their homes in Mexico in the 1960s.
Cruzvillegas referenced the migration crisis and the disappearance of political activists in his native Mexico as influences behind the sculpture.
He said: "My hope is that something can grow, something can happen. This is how I look at it as a self-portrait. I am an empty lot: something that can happen in the worst conditions, something that had only the minimum to happen."
The grid of planters is raised on two triangular platforms that extend the length of the Tate's Turbine Hall and visitors can wander among the supporting scaffolding, identifying where the soils have come from using a map below, or view the plots from the Turbine Hall bridge above.
Empty Lot is the inaugural Hyundai commission, a new series of annual site-specific commissions by renowned international artists and sponsored by the South Korean car manufacturer.
Previous exhibitions in the Turbine Hall have included Ai Weiwei's Sunflower Seeds, Olafur Eliasson's huge artificial indoor sun called The Weather Project, and Carsten Holler's Test Site, featuring giant slides.
Empty Lot will open in the Tate Modern's Turbine Hall from October 13 2015 to April 3 2016.