The ideal way to buy hybrid rhododendrons is to get only plants that have been propagated by layering. These are the costliest of all, because it is the slowest process, but such plants are, as a rule, the hardiest and longest-lived, and there is no possibility of their being choked to death by the miserable stock on which all cheap rhododendrons are grafted.
The "cheap" nurserymen have everything their own way because they have two flashy arguments. First, they magnify the fact that some varieties are worthless on their own roots. The answer is that those varieties are no longer offered for sale on their own roots.
Second, they say that grafted plants grow faster than layered plants. True enough for the first few years, but after that the death-rate is much higher. Any kind of grafted plant has a structural weakness, for the heart wood never unites — only the cambium layer. Consequently it is more liable to be blown over. The worst feature is the suckering and killing.
But it is hard to get rhododendrons on their own roots and if you cannot afford them the next best plan is to buy plants that are grafted low — not high. The higher a plant is grafted, the sooner it reaches a salable height and therefore the greater the profit. But if you will pay a little more, get low-grafted plants and set them a little deeper than they were in the nursery, you give the variety a chance to make roots of its own and eventually free itself from the danger of being killed by suckers.