A private garden need only please its owner; after all, taste is very individual. But while beauty may be in the eye of the beholder, there are some basic garden design principles to keep in mind.
An important consideration that drives the rest of the design is function. How will the garden be seen? Is this bed to be enjoyed primarily by those looking out the window from inside the house? Is it to be viewed by people in cars or pedestrians passing by? Or is the bed part of an outdoor room? Do you want to view the bed while sitting out on the patio, or is it meant to entice one to walk through?
The size of the flowerbed will be determined by factors such as function, and, of course, budget. If you're new to gardening, it's probably best to start small at first -- you can always expand later.
Most garden books advise three basic design rules. Tall plants to the back, complementary color schemes and massing of flowers for effect. In general, you won't want taller plants to block the view of shorter flowers. However, if the bed can be viewed from all directions rather than just one side, perhaps the tallest plants should be placed in the middle, with smaller plants toward the perimeter. For those with a taste for the extraordinary, dare to defy the rules and create a surprise garden by tucking some smaller flowers behind the taller-stemmed plants. This technique can be effective for gardens that invite intimate visits.
Once you've determined a function, decide on a focal point or a center of attention. The focal point can be a plant or group of plants, a pond, a statue or any other object you want to catch the eye. The other elements of your design should serve to enhance the focal point, not compete with it. Because of the seasonal nature of gardens, the focal point can change throughout the year.
Certain color combinations tend to be more pleasing than others, but what is harmonious to one person may be less so to another observer. A useful tool for color design is known as the color wheel. Colors that are directly across from each other on the wheel are known as complementary. Purple and yellow, blue and orange, and red and green are considered to be complimentary color combinations. Analogous harmony uses colors directly next to each other on the wheel. For example, blue and green or blue and violet are also considered to be pleasing combinations. A color scheme using various shades of a single color is known as monochromatic. A multicolored design will tend to have a more informal look.
Grouping many plants of the same texture and color is known as massing. This technique will give greater emphasis to that color and texture and will tend to be more dramatic.
Don't think of your flower garden as a permanent exhibit. Annual flowers will need to be planted new each year. Perennial flowers will come back but they can be moved when necessary. Think of your garden plants much like the furniture in a room. If you've grown tired of the arrangement, change it!