Answer: A newly planted tree should be watered as needed to keep the soil moist but not soggy or sopping wet. You may not need to water as often if there is a good soaking rain. Overwatering can cause a tree to wilt. Also, if there was standing water in the area where you planted, it may be too wet of a location for this kind of tree.
On the other hand, underwatering will also cause it to wilt. The newly planted tree will need to have its rootball (the potting soil) kept moist as well as the surrounding soil. The roots will not grow into dry soil, so you need to water an area larger than the original soil ball. You may need to dig down and actually see how effective your watering is.
One additional note is that if you drove the tree home without covering the foliage to protect it from wind, then it may have suffered from the trip and this may be causing it to wilt. I would also strongly suggest you consult with the nursery where you purchased the tree if it is still looking stressed.
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