The 38-year-old actress reportedly splashed the cash on the drug, which is legal in the state of California, for their wedding anniversary so Robbie - with whom she has daughter Teddy, five, and son Charlton, three - can smoke the substance freely within their mansion, according to rapper Big Narstie, who claims to have seen the farm whilst visiting their home last year.
Narstie - who was at the mansion to work on his 2017 collaboration with Robbie, 'Go Mental' - told The Sun newspaper: ''It was all very surreal. He phoned my booking agent and said, 'Robbie wants to do a tune'. We recorded together. He wasn't what I expected.
''He's very cool. He's very down to earth and a humble person, and he's got a good wife. I saw the present she got him for their anniversary. She got him a whole weed farm in their basement in LA. That's how you drive. It's legal innit? It's legal.''
The 32-year-old rapper's revelation comes after former Take That star Robbie recently admitted he had ''smoked a spliff'' whilst in Queen Elizabeth's residence at Buckingham Palace, where he performed in 2012 for the monarch's Diamond Jubilee Concert.
He said in February this year: ''Threw up in Buckingham Palace? No. I smoked a spliff in Buckingham Palace.''
The 'Angels' hitmaker has been open about his relationship with the drug in the past, and despite having been to rehab twice, he admitted in 2013 that he still uses the substance recreationally.
He said: ''The last time I got high was two days ago. No big drug sessions, mind, just a small amount, purely to relax.''
Robbie has also previously been addicted to alcohol and other drugs such as cocaine and heroin, but admitted that since the birth of his children, he has put his partying ways behind him.
He said: ''I don't want to drink and I don't want to take coke, I'm really pleased I don't take coke but I do think about ecstasy.''
Janelle Monáe parties and drives with her girl squad in the video for her latest single 'Crazy, Classic, Life', taken from her album 'Dirty...
Continuing the softer sound of their 2015 release 'That's the Spirit', BMTH are about to release 'Amo' (January 25th 2019) featuring their newest...
To coincide with the new BBC mini-series adaptation of leporine epic Watership Down, Sam Smith has unveiled a new single entitled 'Fire on Fire'.
Her first single since leaving the jungle on 'I'm a Celebrity... Get Me Out of Here!', Fleur East drops the super-choreographed video for 'Favourite...
Dropping the video for his latest album's second single, 'Excuses', is Olly Murs just months after the release of 'Moves' featuring Snoop Dogg.
Professor Green and Rag'n'Bone Man have teamed up for a heart-wrenching video for their single 'Photographs'.
He released 'Everythang's Corrupt' last month, and now Ice Cube has dropped a video for the record's third single 'That New Funkadelic'.
Dappy has unveiled a new stripped down number entitled 'Count On Me' more than six years after the release of his debut solo album.