Wilting is caused when the plants loose moisture through the leaves faster than the roots can absorb. It is common in newly planted hydrangeas. If the soil remains moist to the touch at a depth of 4", no action is usually needed as they recover on their own by next morning at the latest. If the soil feels almost dry or dry, add 1 gallon of water.

If they remain wilted by the next morning, the plant is having difficulty sending water to the leaves. A too small root system could cause this and result in some stems drying out until equilibrium is achieved and enough water is absorbed to support the growth above ground.

Eventually, leaves that do not get enough water will start to brown out at the edges and the browning will continue inwards.

Another possibility is that the plant has developed root rot due too much watering and-or soil that does not drain well. Daily watering can cause this if the soil does not drain the water off the roots quickly and the roots tend to be in wet soil for long periods of time.

You can skip fertilzing on their first year if you want since hydrangeas do not require much. The potting mix in which the plant came probably has those round fertilizer pellets that the nurseries add. Since the plant is stressed, do not feed it; stressed plants should not be fertlized untilt the problem is correct.

For your hydrangeas, you can add 1/2 to 1 cup of compost, composted manure or cottonseed meal in late April or early May and again in late June. That should do them for the whole year. You can also add a general-purpose slow-release chemical fertilizer like Osmocote 10-10-10 on those two times according to the instructions on the product label.