Got Nature? Blog

In Tennessee, magnolia and the highly invasive ornamental pear trees are in full bloom. In New Jersey, crocuses and buttercups are vibrant spectacles of color. Here in Indiana, flowering dogwood, pawpaw, and red oak have responded to an early spring with a burst of blooms as well. This vibrant display is the result of a mild winter. Unfortunately, there is a downside. A sudden cold freeze after this swathe of warm weather could severely damage blossoms, buds, and significantly reduce yields in fruit and nut trees.

Blooms on pear tree.

Blooms on magnolia tree.

Crocus blooms.

Buttercup blooms.

Growth of a tree or flower is the result of the weather and the perpetuation of its natural growth cycle. To store sufficient resources for the following year, trees use the winter season as an opportunity to shuttle nutrients to their roots. With cold temperatures keeping pests at bay, fewer nutrient resources are needed for defense and maintenance. These nutrients will be shuttled to the branches the following spring to support the growth of buds and blossoms. Interruption in the storage process caused by early spring conditions interferes with nutrient supplies and kickstarts the growing cycle again.

Nutrients once slated for root storage are now being sent to the branches to begin fruit and bud production despite having fewer resources in storage than usual. A freeze that occurs after leaves and buds begin to appear will damage the new growth and likely delay flowering and fruiting until much later in the year when surfeit energy is available to support a second growth effort. While trees are usually able to leaf out a second time, there are often more issues with low yield and early leaf drop.

Pawpaw

Dogwood

Red oak

Also, insect pests, usually subdued by cold winter temperatures are likely to be out much earlier than usual and with greater numbers. This increase in insect presence does not necessarily bode well for plant pollinator populations. If, for example, a tree flowers earlier than honeybee populations are available, then it is possible that those trees will go unpollinated. Also, if other pollinators are also unavailable, there will be no fruits the following year on that tree.

USDA Plant Hardiness Zone Map. Agricultural Research Service, U.S. Department of Agriculture, planthardiness.ars.usda.gov.

Ultimately, the state of our seed, fruit, and nut production depends on two major events; pollination and lack of a cold freeze. If we see a sudden cold snap that damages the trees and eliminates pollinators, then next spring will be a time of sorrow rather than an exciting start to the growing season. The dramatic shifts in weather temperatures over the last decade have led the Department of Agriculture to reevaluate and reassess plant hardiness zones. For the first time in thirty years, an updated map with new zones has now been created, USDA Plant Hardiness Zone Map.

Resources:
Purdue Plant Doctor App, Purdue Extension
Purdue Plant and Pest Diagnostic Laboratory, Purdue Agriculture
Planting & Transplanting Landscape Trees and Shrubs, The Education Store, Purdue Extension resource center
Tree Planting Part 1: Choosing a Tree – video, The Education Store
Tree Installation: Process and Practices, The Education Store

Shaneka Lawson, USDA Forest Service/HTIRC Research Plant Physiologist/Adjunct Assistant Professor
Purdue University Department of Forestry and Natural Resources

Lenny Farlee, Sustaining Hardwood Extension Specialist
Purdue Department of Forestry and Natural Resources