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OSU Extension

College of Food, Agricultural, and Environmental Sciences


Phenology is the study of recurring biological phenomena and their relationship to weather.  Bird migration, hunting and gathering seasons, blooming of wildflowers and trees, and the seasonal appearance of insects are examples of phenological events that have been recorded for centuries.  We have all observed that plants bloom earlier in warm springs.  Insects also emerge earlier when it is warm than in cooler seasons.  Because the development of both plants and insects is temperature dependent, plants can accurately track the environmental factors that determine when insects are active.  For this reason, plant phenology can be used to predict insect emergence.  Indeed, the use of plant phenology to predict insect activity is an old practice, with recorded observations dating back at least 300 years.  In fact, research at The Ohio State University has shown that plants bloom and insects emerge in virtually the same order every year, no matter what kind of weather occurred that winter or spring.  For this reason, the flowering sequence of plants can be used as a biological calendar to predict insect activity, and to time other gardening practices that are dependent on a particular stage of plant development, such as propagation or weed control.  The trees and shrubs planted in the OSU Phenology Garden network sites will be monitored for the first and full bloom, which will assist with identifying insect activity.

growing degree days

Growing Degree Days (GDD) are a measurement of the growth and development of plants and insects during the growing season. Development does not occur at this timeunless the temperature is above a minimum threshold value (base temperature). The base temperature varies for different organisms. It is determined through research and experimentation. The actual temperature experienced by an organism is influenced by several factors. These factors affect growth and development. For instance, depending on the weather, an organism’s temperature may be a few degrees more or less than that recorded. An organism may spend its time in the shade or under direct sunlight. The fertility and nutrient content of the soil directly affect the growth rate of insects and plants. The presence of weeds and precipitation may indirectly influence development. Due to these factors and some other scientific considerations, a base temperature of 50 degrees Fahrenheit is considered acceptable for all plants and insects.

For more information and the methods for calculating GDD, please click here.

Ohio State phenology calendar

To obtain the daily calendar of all the pheologial events occuring in your area, please click here.

USA National Phenology Network

The USA-NPN brings together citizen scientists, government agencies, non-profit groups, educators and students of all ages to monitor the impacts of climate change on plants and animals in the United States. For more information, visit

For more information, please visit the OSU Phenology Garden Network