There are many varieties of apples. Differences in varieties range from skin color to firmness of flesh and variations in flavor. Depending on the variety, there is a type of apple suitable for growing in zones ranging from USDA hardiness zones 3 through 9. Many apples produce better when cross pollinated with a different variety. By planting two different varieties near each other, you can increase yields on both trees. Different types of apples need differing amounts of time below 45 degrees F to produce, or "set" fruit.
The skin of Fuji apples is green with red stripes. Ripe Fujis are crisp and juicy with a sweet, yet tart, flavor. Fuji apples need between 350 and 400 hours of temperatures below 45 degrees F to properly set fruit after pollination. Fujis can survive winter temperatures of between -30 and -35 degrees Fahrenheit, and are suitable for USDA hardiness zones as low as zone 3b. Fujis cross pollinate well with Rome and Braeburn.
Gala apples have skins that range from yellow-orange to red. Gala are crisp, but softer than Fujis and are a sweeter apple with less tartness. Galas need around 500 hours of chilling, or temperatures lower than 45 degrees F. Galas can survive winter temperatures of beteen -30 and -35 Fahrenheit, much like Fujis, and are also suitable for growing places with temperatures down to USDA hardines zone 3b. Galas cross pollinate well with Golden Delicious.
Golden Delicious apples feature a skin that ranges from light yellow to yellow-green. Golden delicious are more tart than red delicious, but are still a sweet, soft apple. Not as crisp as galas and Fujis, Golden Delicious are sweet when picked ripe from the tree. Golden Delicious can survive winter temperatures between -25 and -30 degrees Fahrenheit, making them suitable for USDA hardiness zone 4 and warmer. Golden Delicious require 600 to 700 hours hours of temperatures below 45 degrees F. Golden Delicious cross pollinate well with Gala, Red Delicious and Empire.
Red Delicious apples are bright red apples that are both crisp and soft. When eaten from the tree, they are a very sweet apple. Like Golden Delicious, Red Delicious is cold hardy down to USDA zone 4. Red Delicious require 900 hours of temperatures below 45 degrees F for fruit to set well. Red Delicious are semi-self-pollinating, but do better when cross pollinated with Golden Delicious and Gala.