Planting time will play a huge part in the overall success of your camellias. The idea is to plant at just the right time to give your plant time to acclimate to it's surroundings before climate conditions, such as heat and cold, create stress on the plant. A well established plant will be able to handle these stresses better than new plantings.
To understand what your climate stresses are, you first have to know what your climate is. You should know, but in case you don't, we've got a mini-explanation.
The USA is divided into climate zones. Each of these zones have different requirements for growing plants outdoors mainly based on minimum temperatures. There are many factors that can affect your ability to grow Camellias outdoors, but cold temperatures, are usually the deciding factor.
Climate Zones 8 and 9
You can plant outdoors most of the year, but unlike zone 7 and lower, cold is not as big as a concern as the heat. For this reason, we recommend planting in the Fall. This will give your plant an excellent chance to get acclimated before the heat of the summer. In the event you get a sudden cold freeze (below 30F) you may have to protect your plant. If you do plant in Spring, and you can, just make sure your plant gets adequate moisture and is planted correctly to handle the summer heat stress.
Climate Zone 7
You can plant outdoors, but you are subject to get some pretty cool temperatures. So your main concern should be to plant far enough in advance of cold weather to give your Camellia time to acclimate. You will also want to plan to protect your camellias during the first one or two winters. Spring planting is recommended but make sure you pay attention to summer heat and provide shade if possible or adequate moisture.
Climate Zone 6
Not all camellias can tolerate cold winters of zone 6, but there are some. Planting in this zone is recommended after the last frost. You will need to make sure it is protected from summer heat and for the first two or three winters, while it is getting established.
Planting outdoors in zones colder than 6 is not recommended unless you can protect. Zone 10 is possible to plant but will do best in cool shady environments.