Maryland State Climatologist Office

Growing Degree Days in Maryland:
January 1 - December 31, 2024

This analysis obtains Growing Degree Days and Modified Growing Degree Days for the calendar year from area-averaged daily maximum and minimum air temperatures. These parameters are used to estimate the growth and development of plants and insects during the growing season under the idea that development will only occur if the temperatures exceed some minimum threshold so enough warmth is accumulated. Because the actual development will differ for different plants and insects, and the presence of weeds and precipitation can influence the development, a base temperature of 50°F is generally considered acceptable for all plants and insects. However, this base temperature is best suited for the development of specific crops like corn, sweet corn, soybeans, tomatoes, and a few others.

The Growing Degree Days (GDD) are obtained when a base temperature of 50°F is established for the daily minimum temperature before calculating the daily mean temperature. The Modified Growing Degree Days (MGDD) are obtained when a base temperature of 86°F is set for the daily maximum temperature, and the base temperature of 50°F is set for the daily minimum temperature before calculating the daily mean temperature; these are specific to corn development as no appreciable growth is detected with temperatures lower than 50°F or greater than 86°F. Summary tables can be seen in the following links for Growing Degree Days at several base temperatures in the calendar year.

NOTE: The plots are created from preliminary NCEI's nClimDiv-Daily data set, v1.0.0. Data labeled as scaled on January 10, 2025.

The growing degree days are displayed with the dashed green line, while the modified growing degree days are shown with the continuous green line in the upper panel; the black line shows the 1991-2020 climatology of the cumulative modified growing degree days; the thin red lines display the cumulative modified growing degree days every year from 1951 to 2023. The gray shaded areas mark a range of values in corn development (IPAD, 2023): emergence (82-140), tassel-silk (1024-1740), and physiological maturity (2000-3350). Anomalies with respect to the 1991-2020 climatology in the cumulative modified growing degree days (bottom panel) are displayed with the continuous green line, while those for the cumulative growing degree days are shown with the dashed green line. The vertical dotted red lines mark the start and end of the vegetation period in 2024. The accumulated growing degree days and their anomalies at the end of the year are displayed at the top left in each panel.