Combining parsley and Artemisia creates a dramatic contrast in foliage color. (Photo by Susan Hamilton)

Rule 1: Evaluate herbs for their individual characteristics.

Herbs, just like any other plant, possess specific characteristics that can help you decide how they should be used in different garden situations. They vary in "flower power," foliage color, texture and form (vertical, spherical and horizontal). All herbs possess at least one dominant characteristic, but some herbs may possess more than one, making them useful for more than one reason. One such herb is lavender, which puts on a show of purple blooms in early summer, has beautiful gray foliage and is also very aromatic. 'Opal' basil has bold, purple foliage and a spherical form. Artemisia 'Powis Castle' has silver-gray foliage that is strikingly soft in texture.

Lemon grass and purple Perilla contrast form (vertical and spherical), color and texture. The pink flowers of lemon mint (Monarda citriodora 'Lambada') provide a colorful accent. (Photo by Susan Hamilton)

Rule 2: Create effective combinations.

The secret to a pleasing and dramatic look is to combine plants that possess different dominant characteristics. For example, an ideal plant combination would include one plant with flower power, another with interesting texture and a third valued for its foliage color. Then, of these three plants, each should possess a contrasting growth habit or form (vertical, spherical and horizontal).

As you combine these different plants, pay attention to how their foliage and flower colors go together. Try not to combine more than three distinct colors together. It's okay, though, to combine numerous shades and hues of one color together since they are harmonious.

A gazing ball echoes the flower of society garlic. (Photo by Susan Hamilton)

Rule 3: Use color to bring the landscape together.

Choose a color theme (pinks and purples; blues and purples; reds and yellows; cool colors; warm colors) for your herb garden and then select plants to repeat those colors throughout your garden. Repeating shades and hues of your color ties the design together. Again, try not to use more than three distinct colors throughout your garden. Too many distinct colors can make the garden seem busy.

Think about whether you want to use "cool" colors (blue, green, purple, violet and turquoise) or "warm" colors (red, scarlet, orange, gold and yellow). Cool colors have a serene and calming effect. They typically recede into the landscape and make an area feel larger. Warm colors are dramatic and stir excitement. They jump towards you and bring the landscape closer, making it feel smaller. To create a feeling of length, use warm colors in the front of the landscape and cool colors towards the back.

Keep in mind that harmonious colors (various hues and shades of the same color) are soothing, while contrasting colors (opposites on a color wheel) are exciting. Which colors work well with one another can be a matter of personal preference. A trick of the trade is to visit a greenhouse or nursery and pick flowers and foliage of plants you are considering and mix and match their colors to ensure you select plants and cultivars which will give you the impact you are seeking.

Dill provides vertical interest in this herb garden and provides a sense of enclosure for the seating area. (Photo by Susan Hamilton)

Rule 4: Create tiers.

After selecting your herbs, consider the vantage points of the garden so that you plant in appropriate locations. Identify the highest point of the garden, whether it's the back of a border or the center of an island bed. Tier down to the front of the planting from the tallest plant to the shortest plant. Plant according to height--small plants in the front of the bed, medium-sized plants in the middle and tall plants in the back. This allows your eye to flow smoothly through the garden.

As it grows to maturity, a single cardoon (center) will become the focal point in this herb garden. (Photo by Susan Hamilton)

Rule 5: Arrange plants in drifts.

Herbs planted in drifts or masses produce drama and a more pleasing visual effect than individual plants. How many plants you need to create a visually dramatic drift will vary. Usually groups of three or more plants of one species will do, but some herbs are so large that one plant can create a huge visual mass. Cardoon, for example, can reach a 6-foot spread. Drifts should merge into each other, allowing the garden to have a continuous flow. If you plant in long, narrow drifts, you'll tend to get more show and color than if you plant the same number of plants in a circle.

Create your drifts using Rule 2, where you drift from a plant with a pronounced characteristic to one with a different characteristic, then to another one with a different characteristic, ensuring that each has a contrasting growth habit or form. For visual harmony and to avoid monotony, you want to combine the different plant forms together and not have plants with the same forms or growth habit grouped together.

Rule 6: Consider year-round interest.

To create an herb garden that is interesting all year, combine plants that will peak in their performance at different times. Herbs with colorful foliage such as sage and those that flower during the entire growing season such as calendula can carry your landscape from spring through frost. Winter is the season with the least number of herbs available for providing landscape interest, but rosemary 'Arp', winter savory, germander, parsley, thyme and sage are all great herbs for winter show. Their foliage is evergreen and fragrant, keeping things interesting during this cold, dark season. Fall is another time when it is nice to enliven the landscape. Pineapple sage, Mexican bush sage, Mexican tarragon, goldenrod, Joe-pye weed and tansy are all good fall bloomers.

Rule 7: Add fragrance to the landscape.

Strategic placement of aromatic herbs adds the dimension of fragrance to your garden. Consider placing fragrant herbs near walks, paths, patios, porches and decks where they can easily be brushed or touched to release their scents.

The next time you want a plant with a certain texture or color for your garden design, reach for an herb. Whether using herbs in containers or in grand sweeping beds of drifts and tiers, follow these seven rules and you are guaranteed a dramatic and highly effective herb garden.

Susan L. Hamilton is an associate professor in the Department of Plant Sciences and director of the UT Gardens at the University of Tennessee, Knoxville.