The petite blue, white or lavender-tinged blooms of catmint---sometimes called catnip---makes an ethereal foil for its silvery-grey foliage. The flowering herb's delicate beauty and pungent scent make it a favorite not just of cats, but of gardeners seeking an old-fashioned presence in their gardens. Indeed, catmint is so versatile--even coming in both a regular and compact form---that it's equally at home mixed with other herbs, in the back of an informal cottage garden, repelling flea beetles near the vegetable patch or bordering a formal walkway.
Choose the catmint variety that best fits into your garden. The two main types are Nepeta cataria or Nepeta mussinii. The former grows about three feet tall, with white-to-lavender blooms, while the smaller reaches no more than 18 inches in height and has darker-hued flowers in the lavender-to-dark blue range. (This type is actually N. mussinii, which traditionally goes by "catmint," but the two varieties have become so hopelessly entangled that most people use "catmint" and "catnip" interchangeably.)
Consider the traditional decorative uses of the plant. Gardeners of old paired N. mussinii with roses and lavender. This shorter variety makes a beautiful, soft-edged border in front of those or other ornamentals. The early 1900s volume A Modern Herbal (now available online) advises, "[N. cataria] forms a pretty border plant, especially in conjunction with Hyssop, the soft blues blending pleasingly, and it is also a suitable plant for the rock garden."
Sketch your proposed garden on graph paper, using colored pencils. Place traditional catnip about 12 inches apart from other plants or from each other, if planting in groups. The smaller variety can be placed slightly closer.
Position traditional catmint in the back or middle of the garden. Beds wider than five feet often have three rows of plants, with the taller, three- to five-foot plants in the back, the two- to three-foot plants in the center row, and the low-growing ones in front. A narrower garden will have only two rows, while a border garden might have only single lines of plants along both sides of a garden path.
Consider the foliage and flower colors, shapes and sizes of catnip and its neighboring plants. Catnip doesn't have a reputation for clashing with other plants visually; there are no chartreuse leaves or orange flowers to worry about. Still, contrasting--rather than clashing--textures can be pleasing. In an herb garden, the heart-shaped silver-grey leaves of catnip look beautiful next to the needle-like leaves of rosemary or lavender. For more contrast, choose larger-petaled flowers in pastels or bright colors, such as a yellow rose or peach daylily. These plants "pop" when set against the small-petaled, somewhat spiky blue flowers of most nepatas.
Double-check the specifics on all nursery and catalogue varieties, including catnip. If you're looking for a flower garden featuring all blues and purples, don't order a variety of catnip with white flowers.
When planting season arrives, place catmint and all other new plants, still in their pots, in their proposed places before placing them in the ground. This method gives you a chance to see how the plants look together. Bear in mind that all of the herbs and flowers will become significantly taller and wider than they currently are, and most won't be flowering yet. Still, you can get a sense of how well their textures and foliage colors intermingle.
If fitting catnip into an existing garden, place the potted seedlings in the garden's blank spots and get a sense of how well the catnip flowers co-mingle with the established blooms.