soilless
adjective
soil·less ˈsȯi(-ə)l-ləs 
: having, containing, or utilizing no soil
soilless agriculture
soilless media for starting seeds
Example Sentences
Recent Examples on the Web The tissue is then grown in vitro for a year, and afterwards grown in a soilless mineral solution to gain more biomass. 
Matthew Sedacca, The Atlantic, 17 July 2017
Matthew Sedacca, The Atlantic, 17 July 2017 Word History
First Known Use
1938, in the meaning defined above