Poinsettia flowering can be delayed by as little as 1-2 fc. Use blackcloth beginning about Oct 1 for a minimum of 3 weeks depending on pot size to insure that the poinsettias will initiate uniformly and not be delayed. After that time days should be naturally short enough for normal development. N and K rates can be reduced to about 100-150 ppm N and K if the crop is being subirrigated. Can use slow release fertilizer.
Foliar analysis can be an effective way to determine the nutritional status of the poinsettia.
Once the results are returned they can be compared to the optimum range for poinsettia. Pinching will help to control final plant height because initiation will mean that no more leaves will be produced thus little stem elongation. As a general rule poinsettias can be pinched about 2 weeks after planting when root growth is vigorous. Pinching is the process of removing a source of auxin from the plant. Auxin is the hormone that causes apical dominance so when the source of auxin is removed the auxiliary shoots will begin to develop.