Growing Degree Days

The peak harvest-period in the USA is somewhat predictable according to the pawpaw-tree-variety and according to a climate-metric known as the "Growing Degree Day" (GDD), and typically most varieties of pawpaw need more than 2,400 GDDs to ripen the fruit. The GDD methodology typically uses 50F degree as the baseline-reference-temperature, and May 1st can be used as the start-date for pawpaw fruit (*see footnote). The daily GDD contributions are summed until the fruit ripens. The start-date and methodology can vary according to the purpose of the data as mentioned in the footnote.

Example GDD Calculation for one day: If the 24-hour average-temperature for July 20th is 80F degrees, the GDD contribution is 80F-50F baseline ref = 30 GDD.

New York and Michigan have native pawpaw trees that are challenged for adequate GDDs and they are mapped at the bottom of the page using the US-Degree Day Calculator from Oregon State University. Hence it is possible to find very early ripening varieties in those locations to use in challenged climates.

The GDD method might not be totally reliable in other parts of the world with different climates, but it is the best method currently available. The pawpaw sightings section provides pawpaw ripeness data from other parts of the world to use for comparison.

In the USA, the GDD period begins with the selected start date, and each day's contribution is summed until the peak-ripeness is reached. The following table (*ref footnote) presents the GDD accumulation for some pawpaw-varieties:

* Note: The data comes from Kentucky State University Regional Variety Trial, page 62 with the exception of the KY Champion Tree data which was evaluated in Sparta NC, starting May 1, which is 2-3 weeks later than the Frankfort trials.

Early ripening pawpaws could be found around the Great Lakes in areas with 2,400 GDDs or less: