Look to the color wheel to help envision what colors go well together. Analogous colors: choose one color and know that the shades of that same color should go well together. Complementary colors: choose a color and look to the opposite side of the color wheel for a second color. Triadic colors: envision a triangle over the color wheel for three colors touched by the triangle points.
Potential height of flowering plants might follow one of three themes in your flower garden. (1) All about the same height, which works well anywhere in the landscape. (2) A layout good for plantings that back up against a structure, like a fence, building or tree would be tall in back, medium in the middle and short in the front. (3) For plantings where you can walk completely or almost completely around the flower bed, place the tallest plants in the center and surround them with shorter plants.
Repeat flower groups
A single flower in nature, though not impossible, is an oddity. For a more natural appearance, set the flowers in groupings of odd numbers, like three or five of the same plants in one area. To further capture the abundance and beauty of the flower, repeat the grouping in other locations of the landscape.
Flower combination color ideas
Using the color wheel as a guide to choosing garden flowers, pick colors that you like and then visit your local garden center to compare potential height of flowers (as shown on the plant label) against available flowers of your preferred colors. To help you along, here are some ideas for combing flowers in the garden.
Triadic colors: coneflower (dark pink), moonbeam coreopsis (yellow) and May night salvia (deep blue); balloon flower or Russian sage (blue), daylily or yarrow (yellow or gold), Japanese anemone (pink or rose).
Complementary colors: geranium or carnation (red) and lamb's ear (light green); pansies (purple) and snapdragon (yellow).
Analogous colors: zinnia (orange), marigold (orange) orlantana (yellow-orange); begonia, celosia, or verbena (all in shades of red); different varieties of hostas (greens).
White flowers, like petunia or sweet alyssum, can border flowers of any color or be periodically set throughout a grouping.