I live at Bathurst/Steeles (borderline of Toronto and Thornhill) so, maybe, a zone 6 or 5? I want to plant rhodo and Azaleas in my front yard which gets abut 5 hrs of sunlight and a clay soil. Would a Loderi King George Rhododendron grow at the said location? I read that one has to create perfect soil conditions for the plant. How do I do that? If I need to send a soil sample for testing, where do I send it to? If a Loderi is not recommended, may I know what type of rhodo and azalea would be suitable? When is the best time to plant it? I had 3 cypress trees in the said location which I cut down and want to plant the rhodo and azalea in the same hole this coming year, 2020. I am aware that you cannot recommend a nursery to buy the plants from, so could you give me a list of nurseries in the Bathurst/Steeles area where I could get the plants from? thank you.
Rhododendron ‘Loderi King George’ is stunningly beautiful in flower and a RHS AGM winner; no wonder you are keen to have one. It is winter hardy to -18C so it is borderline hardy in your area (zone 6B, -17.8C). You will need to site it in a sheltered area away from wind and harsh sun, and provide good winter protection.
As for cultural requirements, rhododendrons and azaleas originate from the forest understorey, so they want cool, moist, acidic, organically rich soils, and shelter from elemental extremes. The soil pH must be 4.5-6.0. Their shallow, fine root system demands consistent moisture but also good drainage, and prefers to form a symbiotic relationship with specialized soil mycorrhizae in order to thrive. The soil should also be well aerated and not too heavy.
Generally, clay soil is not a good fit for rhododendrons and azaleas, as clay soil is usually heavy, has poor drainage, and its pH level is notoriously difficult to change. The results of your soil test will tell you what you need to do and how to do it (e.g. what kind of amendments you should use and the amount you will need, etc.). Check this Ontario Ministry of Agriculture and Rural Affairs (OMAFRA) webpage for a list of accredited soil testing laboratories. You can also build a raised bed to improve drainage. Rhododedrons and azaleas are best planted in early spring, or early fall.
For rhododendrons that are more winter hardy, there is, for example, the P.J.M. series, and those bred by Helsinki University in Finland. There are also deciduous azaleas that are native to Ontario. The Landscape Ontario website is a good source to start your search for a garden centre near you. Here is the search result for garden centres near Thornhill.
We wish you the best of luck.