Photoperiod Control
Lighting for Long Days – Long days are needed to allow vegetative growth. Sufficient long days must be provided to obtain the proper finished plant size for a given container. Artificial long days should always be used during mum propagation, and with spring-lighted/shaded
and summer-shaded garden mum programs. Artificial long days can be supplied by lighting plants from 10:00 p.m. to 2:00 a.m. with 10 to 15 footcandles of incandescent light. This can be obtained by stringing 60 to 100 watt bulbs 3 feet apart and 3 feet above plant growing tips. Use a timer to control when the lights go
on and off. This lighting in propagation and before black cloth on summer-shaded crops should be done even when the natural daylength is greater than 12 hours, to ensure the cuttings do not
bud too early.
Black Cloth for Short Days – Short days are needed for flowering. Artificial short days are provided by covering plants with an impermeable light barrier like black cloth or 4 to 6 mil black plastic
for at least 12 hours daily. This can be accomplished by pulling black cloth before the sun sets and opening after sun rise (7:00 p.m. to 7:00 a.m.), or by pulling black cloth early in the morning before the sun rises and opening mid- to late morning (5:00 a.m. to 10:00 a.m.) to help reduce the temperature under the cloth during the night. Light intensity must be less than 1 to 2 footcandles to be effective.
For most predictable timing, covering is recommended every night until color shows on buds; however, some growers have found satisfactory results covering Yoder varieties for only 3 to 4 weeks.
We recommend using 4 weeks until experience is gained with only
3 weeks.
When using black cloth outside of the greenhouse, some growers
are using weed barrier cloth since it allows the passage of air and water, which helps lower temperature under the cloth and prevents pockets of rainwater from weighing down the cover, which can injure plants below. Black cloth can be laid directly atop plants but generally some type of support structure is used outdoors to prevent damage to the crop if windy or rainy conditions occur while covered. A common structure can be made by placing bent 10-foot sections of electrical conduit or PVC pipe at 10- to 12-foot intervals along the bed. The
end pieces of the pipe are inserted into a slightly larger diameter galvanized pipe that has been hammered into the ground. Wire is used to connect the hoop at the top to provide some additional support for the cloth between the hoops as well as help keep the hoops upright. The covering is pulled over the structure at the end
of each day from either the sides or ends of beds, and then unrolled and stored in the side aisles or ends of beds in the morning.