Why is My Christmas Tree Beginning to Grow?

This article was written by Bert Cregg, Michigan State University Extension, Departments of Horticulture and Forestry, and Jill O’Donnell, Michigan State University Extension

Often, Michigan State University Extensioneducators receive calls from homeowners in December because their Christmas tree has broken bud and started to grow while in the house. To understand what is going on, we need to talk about how conifers develop and survive the winter. Each year, trees follow a cycle of dormancy in the fall. This process helps them survive through winter until spring when they will come out of dormancy, de-harden and resume growth.

The two most critical environmental factors that trigger the dormancy process are the reduction of light, or photoperiod, and low temperatures. Conifers will stop growing and set terminal buds as days become shorter even though the day temperatures are still relatively warm, but the nights are cool in August and September. The dormancy process first begins because of decreasing photoperiod, but continues as trees respond to low temperatures around or just below the freezing point. This dormancy or chilling period is needed before normal growth will resume in the spring.

As a general rule, most conifers need to accumulate at six to 10 weeks of exposure to temperatures below 40 degrees Fahrenheit in order to meet their chilling requirement to overcome dormancy. The chilling requirement is an evolutionary adaptation that protects trees from starting to grow anytime they experience a brief warm-up during the winter. It’s the same reason bulbs don’t start to grow as soon as you plant them in the fall.

Some tree species require a relatively short chilling period to overcome dormancy. If we have a cold fall and early winter, trees may accumulate enough chilling hours to satisfy their dormancy requirement before they are harvested from their field or during shipping and display at the tree lot. Once the chilling hours are met, the only thing keeping the tree from growing is that outdoor temperatures are too cold. Once trees are placed in a warm, favorable environment, they can and sometimes do begin to grow like it’s springtime. This can seem like a miracle, but it is just the miracle of nature.

For more information on selecting and caring for your Christmas tree, see the following MSU Extension articles:

• Picking and caring for the perfect Christmas tree
• Selecting the perfect Christmas tree: Tree types
• Keeping your real Christmas tree fresh this holiday season
• Enjoy a living Christmas tree for years to come

Dr. Cregg’s work is funded in part by MSU’s AgBioResearch.

This article was published by Michigan State University Extension. For more information, visit http://www.msue.msu.edu. To contact an expert in your area, visit http://expert.msue.msu.edu, or call 888-MSUE4MI (888-678-3464).