USDA Zones like 9a only tell how much cold a plant will take. So if the camellia is hardy to 9a it will certainly be hardy to 10.

You really need to be referencing your plants against the recommendations in the Sunset Western Garden Book. California has too diverse a climate and geography to be just relying on cold hardiness for suitability.

According to the SWGB, camellias are suited to the San Diego area (Sunset zone 24) with certain caveats: adequately acidic soil conditions - this could be a limiting factor for you - and some protection from the harsh afternoon sun.

Thank you for the advice. Sorry, I should have been more clear.... the camellia is rated for zones 7a to 9b and I’m in 10a. I have to Shi Shi Gashiras in part afternoon sun and they’re doing great, and 3 In the Pinks already. The young Japonicas are also surprisingly taking some afternoon sun very well with no problems. The area I have for the October Magic Ruby would get less sun, I’m thinking it may work???

The bigger the USDA Zone number the softer the winter climate, any time your number is higher than the plant is rated for it will be cold hardy there. As for summer conditions, soil conditions etc. the USDA zones have nothing to do with those.

Thanks Embothrium. So, you don’t think it would be to warm here for this particular camellia? I do have a heavy clay soil, but with minimal soil amendments my existing 5 camellias are doing very well and I had great growth out of them this spring.