The best time of year to transplant an avocado tree is in the spring, typically from February to May. This is when the tree is actively growing, but before the hottest summer days arrive. Summer planting can cause heat stress in newly-transplanted trees that do not yet have feeder roots established, but fall planting can be successful. Sprouted avocado seeds indoors can be transplanted any time of year (although spring is best), especially if they are no longer thriving in water alone.