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Mayfirst, that looks like petal blight. Caused by a fungus, the disease develops during periods of moist weather at flowering time. You'll want to practice good sanitation and remove any spent flowers, litter under your plants. Spraying buds with fungicide (Bayleton recommended) just as they begin to show color but before they open is a good means of control...since you've had petal blight in your garden this season, you might want to consider treating your rhododendrons early next year.

There may not be anything wrong at all. How long were you away? Rhododendron blossoms last on average probably only about 2-3 weeks - quite a bit less if the weather is hot. If only the blossoms looked wilted and not the leaves when you returned home, what you saw is very likely the natural end of the blooming cycle. If, on the other hand, leaves and stems also looked wilted, a dry rootball is a distinct possibility. Shouldn't be happening with professionally installed plants, but the erroneous advice to water every day (a good soaking once a week is much to be preferred) does not inspire confidence. Avoid the Miracle-Gro. Too fast acting, too high in N. I do believe in light early spring fertilization with a slow acting organic type fertilizer such as Hollytone, but that's it.

While some rhododendrons are naturally leggy, others will branch as part of their normal growth pattern and grow into bushy form. There are ways you can tweak this and guide your plants development... If your plant is young, to encourage branches to form, pinch. As the new growth buds begin to elongate in Spring (right around bloom time), snap off/pinch out those terminal growth buds - careful not to mistake the round, fat, blunt-tipped flower buds. A plant hormone is produced by leaf buds which inhibits development of dormant buds along the stems (the hormone is not contained in the flower buds) - removing the terminal growth (leaf) buds will force new shoots to develop from dormant eyes along the stems and the result is a fuller rhododendron with more branching. You'll need to continue this pinching procedure each growth cycle in Spring for two or three years. Growth buds in rhododendrons form in the leaf axils - where leaf joins stem. If your plant is older, cut (sharp pruners)immediately above a rosette of leaves and new growth will emerge form dormant eyes there. In Spring, soon after bloom. If your plant is older than old, you can still do a renovative pruning that will result in new growth, let us know if that's what you are dealing with....