The growing period, developed by the Food and Agriculture Organization (FAO), estimates the time during which crops can grow under specific climatic conditions. It is a key metric for agricultural planning, particularly in regions where water availability or climate variability significantly affects crop productivity. The concept helps guide farmers in selecting crop varieties with suitable growth cycles and in planning planting and harvesting schedules.

The growing period has been widely applied in scientific and technical studies. It underpins FAO’s Agro-Ecological Zones (AEZ) framework and the Global Agroecological Zones (GAEZ) database, which evaluates the suitability of regions for agricultural production based on the integration of climate, soil, and topographic data. Additionally, it is used to assess the potential impacts of climate change on agricultural productivity. Shifts in rainfall patterns and temperature due to climate change can greatly alter the growing period in various regions, affecting crop calendars and food security.

The Length of Growing Period (LGP) is the number of days during a year when temperature and moisture conditions are suitable for plant growth. It is calculated based on a simple waterbalance that models the interplay between rainfall, soil moisture, and potential evapotranspiration (PET).

A typical, a.k.a. ‘normal’, growing period is divided into three phases:
• Start of the growing period: begins when rainfall exceeds half of the PET, allowing moisture to support crop germination and early growth;
• Core growing period: occurs when rainfall consistently exceeds PET, leading to sufficient soil moisture for optimal crop growth;
• End of the growing period: ends when available soil moisture is depleted and rainfall falls below half of PET, leading to water stress and the cessation of plant growth.