|Planting into good soil
If you have free draining soil that is rich and good then you can plant straight into it without adding or doing anything special to it.
If your soil is poor
Simply dig a hole 2 - 3 times larger than you actually need, and fill that hole with good soil, peat or rhodo potting mix.
If you have clay soil
You can plant your rhodo on top of the ground and mound up heavy good soil and mulch around it. One of the largest rhodo gardens we have been to was entirely on a clay pan. The rhodos were all in raised garden beds, none of them were planted into the clay.
Avoid animal manure going into the hole with the rhodo - see more information on Fertilisers
Peastraw helps to keep water in the ground and helps to reduce water evaporation by the sun. It also helps to control weeds. We put our peastraw on thick and usually replace every 2 years.
Rhododendrons must have plenty of water. Without enough water in summer rhodos shut down their flower production for the following spring. Rhodos don't like their feet to be sitting in water, so ensure that the soil is free draining.