Oakleafs in my hot location suffer from wilting when the roots are unable to provide moisture as fast as the leaves loose the moisture. Thus, you can blame high temperatures, windy conditions and too much sun as possible causal agents. If the problem persists long enough, the leaves will brown out.

Because things are not as the used to be, meaning your plant is now older, it must be needing more water than you ave been supplying so far. With the passage of time and with a bigger shrub (above the soil and below), the plant that used to be fine with a certain amount of water now needs more water and/or more often.

To help alleviate this problem, you can maintain lots of mulch (up to 4" or 10.2cm) as mulch will keep the soil moist longer and you will not need to water often. Water only the soil early in the mornings from the base or crown outwards up to the drip line.

If all the leaves have dried out, it still could recover but it will require that you maintain the soil as evenly moist as possible. In other words, try to keep the soil moist -not wet- and prevent the soil from drying out. Periods of dry soil followed by periods of moist soil, followed again by periods of dry soil are not good. You can insert a finger into the soil to a depth of 4" (10.2 cm) and water when it feels dry or almost dry. The plant may leaf out again this growing season or it choose to wait until Spring 2014. If the stems do not leaf out by mid-to-late May, I would then assume that the plant died. Hint... also water it during dry winters if the soil does not freeze. One watering per week or every 2 weeks should be sufficient during the winter months.

Caution: oakleafs can develop root rot quite easily if they remain in wet soil for long enough periods of time. So maintain the soil moist, not wet, and water when the soil feels like it is drying out or when it has dried out.

If your location is windy, consider adding some type of wind break. A garden structure, another plant, etc can help.

Luis

Oakleaf hydrangeas are rather prone to Armillaria root rot, aka honey fungus, which produces a wilted appearance (often very rapid) and will eventually kill the plant. This disease is more likely to develop in a drought stressed plant rather than one that is overwatered. However, root rots like this (and Phytophthora) can develop from all manner of stressors - not enough water, too much water, root damage, mechanical damage (breaking, pruning), etc.

I'd suggest researching these diseases to determine if this is the cause and what you can do, if anything. Armillaria is pretty distinctive in its appearance but you need to see the plant roots to determine for sure.

Unfortunately, root rot diseases tend to affect the vascular system of the plant, disrupting its ability to transport water and nutrients, so when they become obvious additional watering is pointless - the plant is no longer able to absorb it.

This post was edited by gardengal48 on Sun, Aug 11, 13 at 13:37

Sounds like root rot-rarely can you save the plant but part of it may come back. Good luck. I have had it happen here when drought stressed and when too much rain.