If your answer to this question is “by getting longer,” than you’d be correct. Both the EPA and NOAA scientists report the average growing season in the Lower 48 states has increased by 10 days when compared to the long-term average. And a majority of the increase has happened since 1980. Understand, changes in the length of the growing season can have both positive and negative effects on the yield and prices of particular crops. Overall, warming is expected to have negative effects on yields of major crops, but crops in some individual locations may actually be benefiting from a longer cycle. A long growing season could allow farmers to diversify crops or have multiple harvests from the same plot. However, it could also limit the types of crops grown, encourage invasive species or weed growth, or increase demand for irrigation. According to the EPA and NOAA, the length of the growing season is defined as the period of time between the last frost of spring and the first front of fall, or the period of time without the air temperature dropping below the freezing point of 32 degrees Fahrenheit. Below are some key points laid out in a recent EPA/NOAA study. (Source: EPA, NOAA Length of Growing Season)
Average length of the growing season in the contiguous 48 states has increased by nearly two weeks since the beginning of the 20th century. A particularly large and steady increase occurred over the last 30 years (see Figure 1).
- Length of the growing season has increased in almost every state. States in the Southwest (e.g., Arizona and California) have seen the most dramatic increase. In contrast, the growing season has actually become shorter in a few southeastern states (Figure 3).
- Final spring frost has been occurring earlier than at any point since 1895, and the first fall frost has been arriving later. Since 1980, the last spring frost has occurred an average of three days earlier than the long-term average, and the first fall frost has occurred about two days later (see Figure 4).
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