How Do Trees Wake-Up in the Spring?
With this year’s mild winter weather, it is clear that many of the trees have gotten confused and started to wake up early. Although this is fun to see, with the spattering of color around the city and along our highways, it can spell disaster for those trees if winter freezes pop back up.
Deciduous trees, those that lose their leaves in the winter, have an amazing ability to measure when spring is coming. Scientists have come up with an explanation for how these trees measure when winter has ended and why sometimes the trees get it wrong. The explanation is Chilling Hours. Chilling Hours are a measurement of the amount of time throughout the winter that a tree is exposed to temperatures that are between 32°F and 45°F. These hours accumulate quickly during warm winters and when they reach a certain point, determined by the genetics of the tree variety, dormancy is broken and the plant wakes up. It seems like a simple system, but when winter weather strays from the normal, many trees tend to get confused and wake up before the danger of winter weather has past. For our area in the Piedmont, we average between 900-1200 chilling hours in a typical winter. This is important when choosing plant species for the home landscape as well as for farming operations. Choosing a plant with too low of a chilling hour requirement will cause the plant to flower early, while those with too high of a chilling hour requirement are slow to come out of dormancy and will often suffer throughout the growing season.
The fruit industry is particularly worried about early plant growth because many times the first things to come out in the spring are the flowers. These flowers represent the potential fruit load for the season. For crops such as apples and peaches, the flowers are only formed once a year and are especially sensitive to freezing temperatures. This means that if an apple tree is in bloom and a frost comes, it may lose all of its fruiting potential for the entire year.
Plants are amazing creatures and we are lucky to have the ability to understand why they do so much of what they do. Here at the N.C. Cooperative Extension of Randolph County, we are happy to provide all of the plant and gardening knowledge that we can. Please feel free to contact us at 336.318.6000 for more information on this topic or any others in the world of agriculture, family consumer sciences, and youth development.