The goal of season extension is to stretch the active growing period earlier in the Spring and later in the Fall. You can do this by implementing strategic infrastructure or by making careful selections of crop varieties.
Greenhouses, row covers, windbreaks and tunnels (high and low) are commonly used to adjust temperatures and protect plants throughout various weather conditions.
You can get an early start by starting seeds indoors in the late winter and early spring, whether it be under grow lights or on your windowsill.
It is also a good idea to practice succession planting and select crop varieties based on their tolerance to certain temperatures.