While trees, especially young ones, need water to survive, over watering can quickly drown a tree, seriously harming and even killing it. Some signs of over watering, such as wilting, are the same as those of under watering, so it's important to monitor your trees for multiple signs that you're providing too much water. While you should follow nursery recommendations for watering for new trees, certain factors such as wet soil or damp weather call for adjusting your approach.
Inspect the circumference around the tree, at both the base and several feet out from the trunk. Any sign of mold, algae or mushrooms indicates the tree is over watered, as does standing water observed over several days.
Feel several leaves in your hand. If they are green, but brittle, the tree is over watered.
Look at the leaves overall. If they are wilted, this could be a sign of over watering. It is also a sign of under watering, so wilting alone cannot give you a definitive answer. Rely instead on the cumulative signs.
Find young leaves on the tree and assess their color. If they are light green or turning yellow, the tree is over watered. Look also for young shoot growth. If the shoots are wilted, you're over watering.
Feel the soil around the tree for several consecutive days. Stick your finger several inches into the ground, and sink a dowel or wooden handle of a tool down further. If the soil is constantly wet close to the surface over several days with no watering or rain, the tree is over watered. If the deep or shallow holes you create fill up with water, this is a sure sign of too much water.