Growing Degree Days - Hardiness Zones

Growing Degree Days are a measurement of the growth and development of plants and insects during the growing season. Development does not occur at this time unless 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.

OARDC Ohio Growing Degree Days Calculator

Hardiness Zones

USDA Plant Hardiness Zone Map

An Interactive map

http://ohioline.osu.edu/topic/yard-and-garden