I don't know anything about wilting being unique characteristic of LD, but could venture a guess that your problem lays either in TOO sharp drainage (been there, done that in a 12' raised bed) or in unintentionaly left air pocket (if you have a rocky clay this is very possible) where all your water is going, not to the roots.
My suggestion-lift it up and replant properly. You still whole summer ahead of you and should correct problem ASAP to let your plant go into winter being healthy, not stressed.

The most common problem is planting a root bound plant that came from a big box store in a pot. When you get these plants you have to open up the roots so they go out and not round and round. This problem is not always visible. Sometimes they have been repotted and the inner area is what is root bound. Being root-bound causes two problems:

1) The roots are very ineffective, and
2) they are also strangling themsleves.

If you can dig up the plant very gently, insuring that the roots never dry out, you can replant them. I usually just make cuts down the sides of the root ball with a box cutter. Some people aggressively dig out the roots and straighten them out.

This root strangulation is the biggest killer of rhododendrons. It also makes the root balls that are very tight and difficult to keep wet.

Can't remember who posted this on this very forum a few years ago. It explains a lot of things :

"During the last 15 to 20 years, the nursery industry has changed the way they grow and ship Rhododendron's. Instead of in-ground growing, they have switched to growing the plants in containers with an artificial mix as growing medium. This technique allows them to produce a salable plant quickly, effieciently and economically. There is one problem: the typical casual gardeners who purchase the plant in the spring have a terrible time keeping it alive after they have planted it in their garden. It is my guess in reading numerous threads on Garden Web that fully 75 percent of all "containerized" rhododendrons purchased in the spring by casual gardeners "do not live three (3) years" .

Why.

Because the mix in which the roots are growing in the container is so different from natural soil that water will not move into the root zone of the plant after it has been planted. When a gardener plants a containerized plant, he/she creates three(3) different soils; the mix in which the plant is growing; the back fill which should be made up of a mixture of top soil and organic matter, and the great mass of existing soil in the garden. The combination of the back fill and the potting mix will not allow capillary action to carry water from the mass of garden soil to the root ball of the newly planted rhododendron/azalea. Water that falls outside of the root ball has no way to move to the roots. Rain and sprinkles do not do the job because of the umbrella effects of the leaf canopy of the plant.

Spring/Summer planted containerized plants must be hand watered weekly for six months! There are no casual gardeners willing to do that, even if they knew that this was the only way to insure success with the plant. they have never been told that because they probably would not have purchased the plant in the first place if they had been so informed. Of course, if you plant it in August or September, your watering schedule is greatly shortened. The winter is the great equalizer. It brings all three soils back to one colloid and thus allows lateral transport of water to the plant.

Let's take a quick look at what typically happens to our casual home gardener who has just spent a lot of money to purchase a magnificent Rhododendron/Azalea in April or May. Let's say that the gardener plants it perfectly as direction's on the tag. It is Spring and he/she is really turned on to gardening and diligently waters the plant weekly for the next few weeks. The plant blooms and the gardener is ecstatic at the display! It is now the end of May and the plant puts out enormous leaf growth, virtually doubling the amount of laef area. Unknown to the gardener but very apparent to the plant, the soil is still cool and the roots haven't even thought about growing out of the magnificent potting mix in which it has been growing. Why should it?? The mix is moist and loaded with fertilizer from the nursery. The back fill area doesn't compare, and also the cool soil temperature is not conductive to root growth.

It starts to turn hot. The gardener now starts to lose interest in gardening. There are many other joys calling him/her away from the garden and the gardener begins to forget the plant. (It has been watered consistently for six to eight weeks already, that surely should be enough, the gardener thinks). The plant with its double canopy of leaves loses water rapidly in the hot, sunny weather, and since water is not being supplied to the root area because the capillary action has been blocked, the plant " wilts".

Our friendly gardener notices the wilted plant and is surprised because other plants right next to this one are perfectly okay. The gardener waters the plant and to his/her joy, within a few hours it again looks perfectly healthy. The gardener has just learned a lesson. One can skip watering until plant wilts and then water and the plant will respond immediately. That is a "deadly" lesson--to the plant. Even though the plant looks as if it has bounced back, it hasn't. Great damage has been done to the root system by the dessication shock, and repeating it increases the damage. Leaves bounce back, but the rootball never gets fully wet. Many roots are still deadly dry and will abort. By the middle of August when it is really hot, the plant begins to look quite bad. Many leaves have dropped and the "Recovery Watering" does not have the remarkable effect it did in June. Going into winter, the plant is sparsely leafed, with no flower buds,and is a good candidate to die over the winter from "Winter Kill". If the gardener had a one-year guarantee on the plant--Franks Nursery and Crafts, Dome Depot, etc--and has saved the receipt, he/she will be able to replace it next spring for free, but sadly, that is usually not the case.

The chances are good that the gardener "will not" try growing Rhododendron's or Azalea's again. Just talk to any casual gardeners and ask them what they think of Rhodies/Azalea's, or do a search on Garden Web - they are truly magnificent, but "I can't grow them"."

Very informative, thank you. I suppose the only way to try to alleviate the apparent problems created by the nurseries' growing method is to slice open the rootball as rhodyman advises. I have sliced rootballs open on other potted plants, but for some reason (probably b/c of my perception that they are just so finicky), have been afraid to do so with rhodos.

What I don't understand is this: when we dig up/transplant, we must be careful not to harm the roots, i.e., we're always told to dig up the entire rootball (well, that's what I've always been told). How is then that slicing them does not harm them? I know the method works, but I never did understand how cutting into roots when digging has an effect that slicing the rootball does not.

Oliver,

That quote is from the Newsletter of the Willamette Chapter of the American Rhododendron Society and was written by Herb Spady, a past president of the ARS.

Regarding opening root balls, what is important is not breaking off the fine hair like roots. They are the ones that actually are functional in providing nutrients and water. The larger ones are structural. When transplanting, the soil is often packed and brittle and tends to break off the small hair roots. In potted plants, the media is very loose and not brittle and the hair roots can be opened up.

Here is a link that might be useful: Herb Spady's original article.

Thought I would post an update. I did dig it up, opened up the rootball and soaked it in water for about 45 minutes. For several days after replanting, I saw no wilting, after which point, the wilting returned.

If I missed one day of watering, the new growth would wilt and eventually, some of the older leaves began to wilt slightly. The wilting occurred not only in the heat of the day, but in the morning also. The heat of the day for this rhodo may be the morning, however, as it faces the east and gets fairly intensive sunlight until about noon. As before, when I watered, it perked back up.

As a side note, we have only had about 2 inches of rain in all of May and June combined so I suppose that such frequent watering may have been necessary even absent any potential root-bounding problems.

A couple of days ago, I mounded the mulch at the drip line to slope toward, rather than away from the plant. I also sprayed the leaves with Wilt Pruf. Now, to say that the leaves are not wilting would be an understatement--the new growth is pointed directly toward the sky--literally perpendicular to the ground. It is somewhat bizzare looking but at least it appears that the leaves are not losing much, if any moisture.

Whether using Wilt Pruf will do more harm than good in the long run, of course, remains to be seen; I have never seen it recommended on this forum. I understand that it may be commonly used to prevent against certain injuries/conditions occassioned by winter weather, but it is indicated on the lable for use under these circumstances as well.

Wilt-Pruf is normally used when transplanting to reduce transplanting shock and in the winter to protect from the combination of winter wind and sun, especially when the ground is frozen. Wilt proof doesn't do much unless you coat the back of the leaf where the stomata are located. One application on the label is for drought.