There is little as frustrating as a garden that has been ruined by pests, even if those pests are as unthreatening as deer. While there are no flowers that are guaranteed to keep deer away, there are a handful of species that deer find unappetizing or repellent which will make the deer think twice before bending over for a nibble.
A member of the mint family, obedient plant (Physostegia virginiana), also called false dragonhead, is highly unattractive to deer. However, the plant is lovely in a naturalized garden, as it boasts tall spires of bright pink flowers accented by lush green foliage. A native of the eastern United States, obedient plant is best grown in partial or full sun in USDA zones 3 to 9. The plant prefers a slightly acidic, well drained loam, but most soils will work fine so long as they are kept consistently moist. Obedient plant is water hungry enough that it will thrive even in the water logged soils near a pond.
English lavender (Lavandula angustifolia), also called true lavender, is a herbaceous shrub that deer find repellent, thanks to the plant's highly aromatic foliage. English lavender boasts dense silvery green foliage topped with small purple or lilac blooms. The plant is best suited to cultivation in USDA zones 5B to 8A, ideally in full sunlight. English lavender should be grown in an extremely well drained, even rocky soil. Water the plant as needed, but take care not to over water. The plant works well as a border, and its flowers can easily be snapped off and taken indoors, where their fragrance can be enjoyed further.
A member of the mint family, beebalm (Monarda didyma) is an herbaceous perennial native to the eastern United States. The plant is repellent to deer, which dislike the strong taste and aroma of the plant. Beebalm will attract other kinds of wildlife, however--namely bees, butterflies and some species of birds. Beebalm sports colorful, round flowers and broad green foliage. The plant thrives in soil supplemented with organic matter, and plenty of water. Beebalm should be grown in full sun or partial shade. Deadheading spent flowers will help keep your beebalm plant blooming throughout the growing season.