The summer heat has died down. Planting trees and shrubs in the middle of the summer is typically not the best time because you run the risk of your plant material experiencing heat stress. Cooler temperatures also means that you don't have to plant in hot temperatures! Win, win!
The moisture we have been getting combined with the warm temperatures means the ground is soft for planting which lessens your planting labor!
Transpiration is essentially how trees sweat through their leaves. Trees release vapor through their leaves to cool down when it's hot. Always keep an eye on the weather and your plants' specific needs; with that said, you typically have to water less when you plant in the fall.
Root Growth is encouraged
Root growth is encouraged when air temperatures are cooler than the soil temperature. Trees and shrubs won't establish much new top growth in the fall and can have time to establish healthy, deep roots. This sets them up to be stronger plants in the spring. It's a good idea to plant trees and shrubs from now until before Halloween because roots need to grow for about 30 days before the soil temperature drops below 40 degrees. Now is the time!