August 15 is the first day of fall. Even though the calendar says it is a month away all of the plants are in full storing mode and you will have already noticed, here and there, the odd yellow leaves in the trees. By mid-September, a number of the perennials will need to be cut back already.
Usually mid-August is when I turn my lighting system back on as it is finally getting dark enough, and early enough for the lights to have an impact.
Also, this is a good time to start up the hot tub, although many people like to start it up during the September long weekend.
You can do one last fertilizing on the lawn but not after this date, as you will encourage week grass going into winter if winter comes early.
On that note, winter is supposed to come nine weeks after the last pink flowering fireweed has flowered in your area.