In general there are two separate factors which will determine whether a particular apple variety is suitable for your area.
- Winter average minimum temperatures - cold-hardiness
- Summer average maximum temperatures
Cold-hardiness is usually expressed using the USDA cold-hardiness scale, which in the case of apple trees, effectively runs from zone 3 (coldest) to zone 10 warmest.
In practice most apple varieties are suitable for zones 10 down to zone 6, as long as they get enough winter chill hours in the warmer zones. Many apple varieties have been developed which are suitable for the very cold temperatures of zone 4 or even zone 3.
Unfortunately the USDA hardiness zones are often mistakenly taken as an indicator of summer climate suitability as well, which is not the case. For example, many areas of the Pacific North West are in zones 9 or 10 because they have fairly mild winter temperatures. Similarly many areas of southern California are in zones 9 or 10 - but in these areas the summer temperatures are much hotter. Apple varieties that will grow in the cooler summers of the Pacific North West may not be suitable for southern California.
Therefore it is also important to understand the average summer maximum temperatures of your local climate when choosing apple varieties.