Several calls have been coming in concerning poinsettias - here are a few growing tips as you produce a crop.
Fertilizer: 250 ppm of 20-10-20 peat-lite special is best. If you are
growing bedding plants in the same house, it may be more convenient to use
150 ppm and top dress a teaspoon of Osmocote 14-14-14 on the poinsettia.
Poinsettias may be grown to finish using 20-10-20, but alternating with
14-0-14 or 15-0-15 is optimum. Do not use 20-20-20; this fertilizer will
cause your plants to stretch.
Long day/ short day treatments: Poinsettias flower naturally between
November 21-December 21. Pulling a black cloth over the plants is not
necessary unless there is bright outside light entering your greenhouse
between sundown and sunup.
Light: Poinsettias need full sunlight. Take your shade cloth off. If you have other plants that need shade, pull the shade cloth back and allow full sun for your poinsettias and shade for the other plants.
Height control: Most schools grow Freedom poinsettia varieties and you may be able to finish these plants without growth retardants. If you are pushing these plants with fertilizer, heat, and plenty of light, they would be helped by an application of growth retardant. If you are growing other varieties, a growth retardant may be necessary to keep the plants from stretching. This is especially true for the schools in the Central and South Regions that are growing the white variety, Snowcap. This is an aggressive variety and must have a retardant to keep them within a desirable height. If you plan to use a regulator, apply it before October 15 or the bracts size will be reduced. Here are some growth regulators and rates. Remember that plants should be well water and the leaves allowed to dry before you spray.
Cycocel - Use 1 ounce per gallon (1000 ppm) of water on Freedom varieties and 1 1/2 (1500 ppm) ounces per gallon on taller varieties. Spray on a cloudy day or in late afternoon.
B-Nine - Use 3 tablespoons per gallon (3,700 ppm) of water. Spray on a cloudy day or in late afternoon.
B-Nine / Cycocel mix - This is the most effective way of controlling height. Use 2 tablespoons of B-Nine and 1 1/2 ounces of Cycocel mixed into one gallon of water. Spray on a cloudy day or in late afternoon.
Bonzi spray - Be careful with this; too much and the plants may never grow again. Use .8 to 1.5 ounces per gallon of water( notice that is 8/10 of an ounce per gallon). This is not a very soluble mix; shake it often while you spray. Spray during a sunny day.
If you get to November and your plants look like they are going to be too tall, you can use a Bonzi drench to stop their growth.
Heat: Keep the night temperature at 64 degrees. We are beginning to have some cooler nights interspersed with the warm nights; make sure you are heating on the cooler nights. The poinsettia varieties grown now are designed to be grown in a short time period, but you must push them with heat, light and fertilizer. If you allow the plants to experience more than two or three cool nights, your plants will be short and late.
Pinching: Plants should have been pinched between September 7 and September 14.
Waiting beyond these dates will cause the plants to be too short. Count
5-7 leaves or nodes from the bottom of the plant and remove all growth
above that point. Pinching at the correct time is critical to quality, but
make sure the plants are well established before pinching. Established
plants will have roots around the edges of the soil. Gently tap the plant
out of the pot (don't disturb the soil) and check for roots. Healthy roots
will be white in color. If roots aren't visible around the exterior of the
soil, you may need to wait for another week before pinching. Do not check
every plant; looking at 4-5 plants should give you a good representation of
Insecticides: Whiteflies are a serious pest of poinsettias. It is almost
impossible to control whiteflies without Marathon. Application of Marathon
should take place about 3 weeks after planting. The insecticide is a
systemic and a good root system is necessary for the plant to take up the
Marathon. If you see whiteflies before the Marathon is applied, use
Orthene, soap, or Sanmite to kill the early insects. If you have other
plants in the greenhouse, make sure they aren't the source of your
whiteflies (lantana is often a host for whitefly).
Use 6 to 12 oz. Banrot 40% wettable powder per 100 gallons of water. If you are using the Dosatron at a 1% or 1:100 setting, you can use 6 to 12 oz. Banrot per gallon stock mix. If using a hozon - I think they have a 1:16 ratio - use 1 to 2 oz. per gallon of stock solution. (To be precise, it is actually 0.96 oz to 1.92 oz per gallon stock solution)