Answer: In my experience, in hot summer areas, these plants prefer sun all morning or bright dappled light all day. The shock of hot afternoon sun is difficult for them to withstand, especially when transplanted at the most stressful time of year -- mid summer.
These plants generally do best in an evenly moist yet well drained soil that is acidic and humusy. The moister the soil, the more sun they can handle in relative terms, but the soil should never be saturated.
Sometimes a newly planted plant is over or underwatered, either can be indicated by the wilting. You would want to dig down into the soil an inch or two and make sure it is moist but not sopping wet. Check both the potting mix and the surrounding soil, sometimes they drain at different rates. Water deeply, wait a few hours, then check to see how effective your watering was. Sometimes it can be surprising.
Your goal is to water to supplement rain to keep the soil evenly moist, but you do not want to drown the plant either. If it is wilting in the heat of the day but recovers in the evening, it is probably moist enough adn simply suffering heat stress. If it is still wilted in the morning, usually that is a sign it needs water (or has been flooded).
Also, use several inches of organic mulch over the root zone but not touching the stems. This will help keep the soil more evenly moist as well as bit cooler.
I hope this helps you troubleshoot. Good luck with your viburnum, it is a lovely plant!
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