The answer to 'best time for landscape design' is that the best time to plan and design your landscape is during the fall or winter months. This allows you to have your design ready to implement in the spring when the optimal planting season begins.
Planning your landscape during the off-season gives you time to thoroughly research plants, materials, and design ideas that will work best for your property and climate. It also allows you to get on a landscape designer's schedule before their busy spring season starts. This ensures you can get your project completed in a timely manner when the weather is ideal for installation.