Clipping should be used to increase seedling uniformity and maximize the number of usable seedlings per tray. It should be used to hold seedlings only in emergency situations where field conditions do not allow transplanting. By paying attention to fertilization and seeding date, clipping can be minimized. Due to increased plant density and potential for producing "leggy" seedlings, management of clipping becomes more critical as the number of cells per tray increases.
Mower maintenance is an integral part of successful clipping. The blade must be kept sharp. Keeping the mower underside clean and slick will reduce the amount of clipped matter that falls back on the plants. Since clipping is an excellent way to spread disease, good mower sanitation is vital (see disease section). RAISED MOWERS CAN BE VERY DANGEROUS. EXERCISE EXTREME CAUTION!
Begin clipping early to establish uniformity. Clip lightly at first to minimize plant shock and to reduce problems with clippings falling back onto the plants. Do not clip closer than 1\2 inch above the bud. Clip as needed to maintain uniformity and prevent excessive stem length. Five to ten clippings should suffice. In 2009, a survey indicated that most growers clip an average of 8 times. If more clippings are required, seeding date and/or the fertility program should be modified for the next year. The reduced phosphorus programs given in the fertility table should minimize the need for clipping. Virginia research suggests the following clipping programs: Begin clipping when plants are 2 - 2.5 inches tall (to bud). Set the mower 1 - 1.5 inches above the bud. Clip on 3 day intervals for first 3 clippings and 5 days thereafter.