One obvious reason to plant in the fall is that you have been through the season, and know what you would like to add and tweak. Do it while it’s fresh in your mind.
Because temperatures have dropped, transplanting is less stressful on the plants — and on you! The lower temperatures make watering easier — plants will still need watering until established. In the fall, perhaps once a week will be enough, as opposed to every other day in the heat of the summer. Feel the soil a few inches below the service and if it is dry, water. It’s always best to water slowly and deeply.
Soil temperatures are warmer in the fall than in the spring, so root growth will be quicker than in the spring. You can’t SEE the root growth, but it will be happening.
Don’t worry about a frost here or there. Frost will stop the growth ABOVE the ground, but the roots will keep growing until the soil freezes solid.
Trees, Shrubs, or Perennials — Does it Matter?
What About Winter?
If you plant this fall, next spring you can enjoy the spring weather, watch your new plants blossom, and weed and tweak. You can shop for new plants at your leisure, filling in spots you weren’t able to get to in the fall.