If you're looking to spruce up your garden or lawn, the best time to start landscaping and planting trees, shrubs, and perennials is in the months of April and May. These spring months will give your plants the opportunity to grow and acclimate during the summer and fall. It's a great time to turn around your flower beds and gardens, and come up with a plan for what you would like to plant. As spring turns to summer and more consistent temperatures arrive, it's a good time to start planting.
September, October, and November are also good months for preparing your lawn for the harsh elements of the coming winter. The cooler temperatures and higher humidity of autumn make it an ideal time for planting larger trees, shrubs, and perennials. Most plants that die within a few months of being planted do so because they weren't planted properly or because they weren't watered properly; it's rare for a tree or shrub to die from insects or diseases during the first year of planting. You should take advantage of the fall months to assess the condition of your irrigation system and determine potential problem areas for winter drainage.
In addition, watering should be prepared for the cold winter months ahead by proper winterization. Soil can dry out and compact during the hot, dry summer months, and once fall rain hits, water buildup can reveal where drainage needs to be improved. Keep in mind that these are general guidelines; transfer any of the tasks a month earlier or later to adapt to the growing conditions of your climate and landscape. With careful planning and preparation, you can create a beautiful garden that will last for years.