"I accept that the cultivation of this cannabis was on a small scale, and this was not in any way a commercial venture on your part. Nevertheless you used a sophisticated growing system to do so," said judge Timothy Workman.
"I give you credit for pleading guilty at the earliest opportunity, your co-operation with police and the fact that you are, until now, a man of good character," added the judge at London's City of Westminster Magistrates Court.
Innis was sentenced to six weeks' custody in a young offenders' institution, and fined 500 pounds (820 dollars, 580 euros).
The pair were detained in April after Waylett took a photo of police while driving past a group of officers. Innis's car was stopped, and police found eight bags of cannabis and a knife.
When police looked at Waylett's mobile phone to see the picture he had taken, they found other photos of cannabis plants. Officers then searched the home of his mother in Kilburn, northwest London, and found 10 cannabis plants.
Another three bags of cannabis were found in Innis's possession. Innis admitted possessing a knife and having 11 bags of cannabis.
Waylett appears as the overweight, greedy and dim-witted sidekick of villain Draco Malfoy in all of the films about boy wizard Harry.
The charge against him in April was announced just hours before the Potter stars walked up the red carpet in London for the world premiere of the sixth film, "Harry Potter and the Half-Blood Prince".
Tabloid newspaper The Sun reported at the time that the cannabis plants could have produced drugs worth 2,000 pounds, printing its story under the headline "Harry Pothead".
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