Some of our poinsettias, different varieties, have single stems on the plant that are completely wilting, eventually breaking off. The rest of the plant looks fine and the roots look good, no signs of disease anywhere. I thought it might be breaking off from walking thru the plants or maybe too many branches for the plant to support. However, I can't easily see any signs of breakage at the base of the stem and it's even showing up on plants in the middle of the bay that don't get any foot traffic. It has also occurred on plants with only 2 or 3 other branches. What could this be?

Erine,
Poinsettias appear to be more prone to side branch stem breakage when...
(1) Too many side branches are left on the Poinsettias and the lower branches looking for light grow in a more horizontal position which puts too much pressure on the joint.
(2) The Poinsettias were at some point spaced too close together causing weak side branches from lack of light after the final pinch period.
(3) Not enough calcium was used in the feed program to produce robust, strong side branches.
(4) Poinsettias were pinched too early or allowed to grow too tall adding weight on the side branch joint.
There may be other reasons for this problem but these have been my observations over the years...
Michael Pawelek Pecan Hill Nursery
PS- There are certain varieties of Poinsettia that have thin stems and need careful attention to the ideas listed above. Even though you cannot see any breakage where the side branch connects to the main stem I believe there is in fact a microscopic break that damages the vascular system and causes the wilting. Once the side branch wilts it will never repair itself and the branch needs to be removed so it will not cause fungal entry into the plant later on as it deteriorates further.

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

I'll pick reason number 3! I think when we have really warm temps around pinch and as the breaks are elongating (like this year), the plants grow too quickly and are not taking in enough calcium. Freedom seems to be very prone to dropping branches, tho others are doing it this year. Last year was much cooler, esp. in Sept., and we had no wilting branches. I'm planning on getting a light shade cloth to use later into the fall and begin calcium sprays much sooner next year. Maybe a calcium IV on each plant...hmmmm....

erine -

Stem breakage can be a mystery to many growers because after a close visual inspection many time growers can't even see any signs of damage or an obvious break in the stem. It can also be random throughout the greenhouse and certain cultivars such as Freedom can be a little more prone to stem breakage.

Michael did a good job highlighting the factors that can contribute to stem breakage. The only thing we would add is that low light levels and warm growing conditions can contribute to weak growth. With the hot summer we had many growers have had to use a lot of shade to try and reduce temps in the greenhouse. When temperatures are warm in the greenhouse it is best to have light levels that support the high temps rather than excessive shade and warm temps. This may not be the case for you but this is just another factor to add to the discussion.