There is a certain order to planting. Following the proper steps will save time, money and energy. The most common mistake is to arrive home with plants before knowing what is needed. Preparing the site before installing the plants is very important, too. Knowing what your objectives are before ever going to the nursery will result in a much better design.
Draw a Site Plan
Do any demolition first. Remove unwanted trees and structures from existing landscapes. If it is new construction, clean up any building materials laying around. When trees and larger plants are removed they alter light conditions. Finish any new hard-scaping. Now draw a sketch of the area to be planted. It is easier to visualize with the unwanted items removed and the area cleaned up. Record the light conditions from each angle in the morning and the afternoon. This will help you decide which plants are better suited for your garden. Dig soil from several areas of the site to determine the quality. If you need to bring in good soil, do this first. Pay attention to moisture levels so you can address any drainage issues.
Make a Plant List
Now that you know the conditions of your garden you can make a plant list. Look up the cultural requirements for each plant. If they are not suited for your site don't buy them. It is good to have back-up choices in case some plants are impossible to find. Know the mature size of each plant so you can allow enough space. Take your list with you to the garden center.
Experiment Before Planting
Before deciding where to put your plants, move them around. It helps to see the actual plant in the spot you have chosen. There is still time to change your mind. You might discover that you need to buy more plant material. This will help you avoid transplanting because you are unhappy later.
Fall is the best time to plant. Early spring is almost as good but you will need to water more the first summer. Start by planting trees and large shrubs. Then install the rest of the woody plant material. Think of these plants as the permanent structure or skeleton of the garden. Herbaceous plants that die back are easier to change later. Most plants should be installed at the same depth they were at in the container. If they look as though they are too big for their container, dig a larger hole. Choose a cool day to install plants. Early morning is the best time of day because the sun is low. The afternoon sun pulls too much moisture from plant foliage. Plants are more subject to wilt while the roots are not yet established. Fill the planting hole with water and allow it to soak in before placing the plant in the hole. After installing the plant and filling in the hole, water again thoroughly.
The First Year
It makes little sense to do everything right and have unhealthy plants because of neglect. Plan to nurture your new plants the first year. Be very attentive to water needs. If necessary set up a temporary drip system to deliver regular water to the roots. Fertilize modestly for awhile, the roots need to grow more than the foliage.