A cannabis factory was found by police when a passing patrol smelt the plants outside the house in Blackburn.
The Police Community Support Officer grew suspicious as he walked past the property in Windsor Road on Thursday.
A search was carried out and 40 plants and growing equipment including lights and fans were recovered.
No-one was at the house at the time and Lancashire police are urging anyone with information about the drugs to contact them.
It was the second time in two days a Lancashire police officer had sniffed out drugs.
On Thursday afternoon, a police officer in Burnley noticed a strong smell of cannabis coming from an address on Scarlett Street.
Officers searched the house and discovered six ounces of skunk cannabis in an upstairs bedroom with an estimated street value of about £900.
A 23-year-old man was arrested on suspicion of possession with intent to supply cannabis and has been released on police bail.
Meanwhile, drugs thought to be amphetamine and cannabis were seized in a raid on a house in Chorley.
Police raided the house on Pennine Road on Thursday evening and found the drugs along with a small quantity of tablets.
A 43-year-old woman and 34-year-old man were arrested on drugs charges and released on police bail.