Is there any feed or other treatment, soil or foliar app., that you can do this late in the season (partial color) to increase leaf and bract expansion without getting the increase in height?

Erine,
At this stage of the Poinsettia crop during bract expansion keep your soil EC levels in the moderate range and try to keep your pH between a 5.8-6.4 if possible for greatest nutrient availability across the board.. By now you should be switching to a feed mix with less and less ammoniacal nitrogen and more nitrate nitrogen. The nitrate form of nitrogen does not allow stem stretch as much as the ammoniacal forms of nitrogen. In my case forcing faster color up and larger bracts is more a function of higher average temperatures. I keep my crop about 68F at night and let the temperatures during the day go up to 85F if I really want to force faster color. Naturally this can be over done and the quality of the color might suffer if temperatures are too high. I also realize many of you further north cannot get your houses this warm this late in the season but in the South it is no trouble at all. Hopefully the Ecke team will write in with better information on feed and temperatures to use at this stage of the crop.
...Michael Pawelek Pecan Hill Nursery

This message has been edited. Last edited by: Michael Pawelek,

erine -

Optimal temperatures for flower development are between 73-78F (23-26C) average daily temperatures. This temperature range also produces the largest bracts. Cooler temperatures will slow bract development and reduce bract expansion. On the other hand at warmer temperatures bract expansion can be too fast and bracts can become floppy and in some cases the color faded.

If height is an issue you should think about using a negative DIF or morning drop. When night temperatures are warmer than day temps the result is a negative DIF which reduces stem elongation. This can be difficult to achieve and the result is an average daily temperature that is less than optimum for bract expansion so many growers use the morning drop instead. This is a really effective way to control height without reducing your average daily temperature which would slow bract development. If you aren't familiar with the morning drop, this is a technique many growers use where temperatures are dropped just before sunrise and kept cool for two to four hours until temperature control is lost. The result is a moderate negative DIF response.

Fertility doesn't really play a role in bract expansion but it is a factor in the growth rate of the plant. By now you should be switched to a nitrate based form of nitrogen. This will help slow growth and tone the plant. Begin reducing rates and plan to be done fertilizing all together about 10 days prior to sale. This allows the EC levels to drop in the soil which will increase post harvest life.