Amount of time, or heat, required to mature a specific hybrid can be expressed in several ways. Use of "Growing Degrees" is a common method. The formula is:

* Use 86 if maximum temperature exceeds 86° F.
** Use 50 minimum temperature if less than 50° F.

The GDs are accumulated through the appropriate period or season. GD is a relative rating and should not be associated with absolute days. For example, on a day when the low is 48° and the high is 90°, the GD is determined as follows: