VIETNAMESE cannabis growers made a million pounds out of one small house in Milford Haven before police closed down the operation, a judge heard on Tuesday.
They got away with at least three crops and there were still more than 430 plants growing towards maturity when police broke in.
Ho Hoang, aged 29, admitted cultivating cannabis but told police he had been only a gardener making money to send to his family in Vietnam.
Hoang, an illegal immigrant, was jailed for three years and told by Judge Huw Davies he would be deported after serving his sentence.
Swansea crown court heard how the letting agents for the house in Robert Street became suspicious and contacted the police. Officers could smell cannabis as soon as they pushed open the letterbox.
Craig Jones, prosecuting, said officers discovered a sophisticated cannabis growing operation which included powerful overhead lamps, fans and an air filtration system.
The 430 plants could have produced 36 kilos of cannabis with a street value of £360,000.
Hoang, the only occupant, was arrested and told police he had seen at least three crops harvested.
He said he had travelled from Vietnam via various countries, even though he did not have a passport, and arrived in the Uk in 2009. At first he was employed as a nail technician but work dried up and he gave into temptation when a fellow countryman asked him to look after cannabis plants in return for between £600 and £900 a month.
Judge Davies said each crop would have produced hundreds of thousands of pounds worth of cannabis and serious offending at that level could be met only by a substantial prison sentence.
He warned Hoang not to expect to be released after serving half the sentence as he would be kept in custody while the authorities arranged his deportation to Vietnam.