Poinsettia

Question:

I kept my poinsettia alive all summer. When should I begin putting it into the closet each night so it will bloom for Christmas?
- Karen H.
   Albuquerque

Answer:

You should have begun the long night treatments at the time of the autumnal equinox (September 22). After this date, the days began to be shorter than the nights. However, if you start the dark treatments now, you may still succeed in having the red bracts (colored leaves under the flowers) in time for Christmas. Some modern varieties do not require as much time as the older varieties to induce flowering. It is possible that they will not be ready for Christmas, but then you can have Valentine poinsettias, so begin the treatments now.

You described one good method for inducing flowering, putting the plant into the closet. Some people have a problem with this method because they forget to move the plant each day. They may forget to put it into the closet early enough each evening, or they forget to remove it from the closet for days at a time. Another way to treat the plant is to leave it in a sunny window, but cover it with a black plastic bag or black cloth before turning the lights on in the evening. There is a hazard in this method because if you forget to remove the plastic bag in the morning, the sunlight will generate enough heat to cook the plant and kill it. If you are likely to forget to remove the plastic bag, consider using black fabric or move the plant farther from the window each evening when the cover is put on the plant. The floral induction process will be enhanced if the night temperatures are allowed to drop to about 60 degrees F. at night.

A few days in the closet or forgotten under the cover of plastic (away from the window) will not kill the poinsettia, but if left in the dark long enough (a week or more), the plant may be damaged. If it dries while forgotten, it will die or at least drop its leaves and become unsightly.

Since this is also a time when many people travel for a few days to visit relatives, some preparations may be needed for your absence. Since you will not be there, room lights during the evening should not be a problem, but don't use an automatic lamp timer (security device) in the room with the poinsettia. Another thing to consider is the presence of a nearby street light that shines on the poinsettia at night. This can delay or prevent flowering.

If you will be gone for only two or three days, water the plant well before leaving. If traveling for up to a week, you may put the plant into a clear plastic bag to maintain humidity and reduce drying. The top should not be sealed unless you will be gone for two weeks or more. These preparations should prevent excess drying during your absence. Remember to remove the plant from direct sunlight if it is enclosed in a plastic bag.

For long absences, you should ask a friend to water your plant occasionally. Remind them to do this during the day and to be sure all lights are off in the room with the poinsettia when they leave. If they must come at night and turn the lights on, this may delay flowering but should not prevent flowering if done only a couple of times.�

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!