by Myron Dellinger, Guernsey County Master Gardener

The word phenology is Greek and means “the science of appearance”. Phenology is the study of recurring biological phenomena and their relationship to climate. 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 ages. Phenology is not the same as folk forecasts such as whether Punxsutawney Phil will see his shadow and the burden us with six more weeks of winter. Or whether woolly bears caterpillars can predict the severity of the upcoming winter by the ratio of brown to black coloration.

Some of the important things gardening phenologists keep track of are the first and last frosts, when the ground freezes and thaws, the best time to hunt morel mushrooms, the planting and blooming of herbaceous and woody landscape plants and the emergence of insect pest. I’m sure you’ve heard the saying “plant corn when the oak leaves are the size of a squirrel’s ear. We all know that planting corn has nothing to do with or leaves or squirrel’s ears but over time, farmers have learned that when the oak leaves have reach this size, the soil is warm enough for corn seed to germinate without rotting in the soil. This hold true for all warm-season annual plants.

Because the development of both plant and insect is temperature dependent, plants can accurately track the environmental factors that determine when insects are active. This is old practice, with recorded observations dating back at least 300 years.

 A prime example would be the Eastern tent caterpillar egg hatch which coincides with the budbreak on flowering crabapple and wild plum – their most common host plant. Looking for and controlling this pest at this early stage is much more successful than waiting until they have defoliated your plant. Research at the Ohio State University has shown that plants bloom and insect emerge in virtually the same order every year, no matter what kind of weather occurred that spring or winter.

The flowering sequence of plants can be used as a biological calendar to time gardening practices that are dependent on a particular stage of plant development, such as propagation and weed control. Crabgrass, the bane of most gardeners, germinates when then soil temperature at 4 inches stabilizes at 55 degrees. This correlates roughly when the forsythia is in bloom and when the lilac is in early flowering stage.

If we would continue to rely on the same lilac we could safely plant cucumbers when the lilac flowers begin to fade.

 Phenology also observes the relationship between events and local weather conditions. You may recall hearing some of the following rhymes and sayings to predict future weather.

Seeing caterpillars about later than usual in fall indicates a milder winter.


Silver maples show the lining of their leaves before a storm.


When the sun goes to bed red,  twill rain tomorrow is said.

Phenology can be more than just a hobby for gardeners, it can become a way of life. For centuries farmers have relied on the signs of the seasons to help them grow a crop.

You too can use phenology to develop your own calendar and grow a beautiful garden.  For additional help and information visit the OSU Phenology Garden Network at