Farming takes place throughout the year, with two Planting/Harvesting cycles in the spring and summer. There is no farming work during the Winter season.
Each growing season consists of 3 months of planting Crops and 1 month of harvesting Food. During the harvest months (March, October) Farmers extract the planted food and store it in the settlement.
Farmers can only harvest Food from the planted Crops. Therefore, it is important to ensure you have enough farmers planting to have a big enough harvest, and enough farmers available during harvest so that planted Crops do not go to waste.
During the winter months Farmers get a break! Use them to build things, or put them in an army to get ready for the spring campaign