While growing a poinsettia outdoors is possible in some areas, it can be difficult to make them turn color in time for the holidays. The poinsettia is a tropical plant native to Mexico. The plant needs specific conditions in order to make it turn the deep red and green it is famous for around the Christmas holidays. Therefore, while growing a poinsettia outdoors may be an easy task in some tropical and semi-tropical areas, making it turn color can be an entirely different story.
The first thing to do is make sure the poinsettia will be in an area that does not get too cold. Any below freezing temperatures could kill the tropical plant. Generally, in order to ensure the plant remains safe from cold temperatures, the United States Department of Agriculture recommends a growing zone of no lower than 10, which usually means temperatures stay higher than 40 degrees Fahrenheit (4.44 Celsius). It may be possible to grow a poinsettia outdoors in zone 9, but that will require diligently taking precautions during sporadic freezes.
In order to ensure they survive freezes in borderline zones, it may be necessary to take some precautions. Planting poinsettias near buildings or covering them during colder times are both common tips. Using warming lights is another way to stave off freezing temperatures for a few hours. Even if they are damaged by cold weather, poinsettias may eventually come back.
Watering and fertilizing are other key areas to consider when growing a poinsettia outdoors. Generally, poinsettias will require no supplemental outdoor watering. If it is a particularly dry area, then watering may be necessary if the soil ever becomes dry to the touch. Growers may use a fertilizer after the holidays. Fertilizing during the holidays could affect the quality of the plant.
It is also important to prune plants, generally in the late winter or early spring. Cutting off fading portions of the branches, leaving at least 4 to 6 inches (10 cm to 15.25 cm) of the branch is recommended. If the plant is potted, but grown outdoors, then the springtime is the time to re-plant it in a slightly larger container.
In order for the leaves to turn before the holidays, having the proper amount of darkness is key for a poinsettia outdoors. The plants must experience at least 14 hours of total darkness in order to turn. Generally, this process should begin six to eight weeks before the grower wants the most vibrant colors. In order to accomplish this, the grower may need to take the plant into a darkened room.