The normal date of bud initiation in most parts of New York is around October 10 and plants should be well established in small pots or pans before this date. By later propagation, shorter plants can be obtained. To be safe, the last propagation should be stuck no later than the first week in September. If plants are pinched, it should be done 4 to 5 weeks before the date of bud initiation. Artificial light should be used from September 15 to October 10 to prevent premature budding. Artificial light supplying 10 foot candles at the top of the plant for two hours in the middle of the night will insure vegetative growth.
Source: • New York State Flower Growers Incorporated, Bulletin #129