Heliotrope

Heliotrope (Heliotropium arborescens) produces dense, flat clusters of deep purple, lavender, or white flowers with a vanilla fragrance and deeply crinkled dark green leaves. It's sometimes called cherry pie plant because of the cherry undertones to the vanilla scent. Heliotrope is a tender perennial that can be grown all year outdoors in Zones 9-11 (in Zones 8 and colder, grow it as an annual).

Stock

Stock (Matthiola incana) and evening stock (Matthiola longipetala) may sound like soup bases, but they're clove-scented biennials (plants that take two years to set seed and die) that are often grown as annuals. The dense clusters of white, yellow, red, pink, or blue fragrant flowers are favorites for bouquets. Evening stock is more sprawling, with more narrow flower petals that open in the evening.

Flowering Tobacco

Two types of flowering tobacco, Nicotiana alata and Nicotiana sylvestris, offer fragrance in beds, borders, and containers. Old-fashioned varieties are your best bet; many newer hybrid bedding-plant varieties carry little scent. All are relatives of tomatoes and peppers, with white, pink, red, or pale green blooms that offer scent in late afternoon or evening.

Four O'Clock

Four o'clock (Mirabilis jalapa) earned its common name because its fragrant flowers open in the late afternoon. A tender perennial hardy in Zones 9-11, but grown as an annual through most of North America, four o'clock's trumpet-shaped blooms are red, pink, white, or yellow and sometimes striped.

Sweet Alyssum

It's too bad that sweet alyssum (Lobularia maritima) grows so low to the ground: The mounded masses of tiny white, pink, lavender, or violet blooms smell like honey. You can bring this groundcover closer to nose level by planting it in containers, window boxes, or hanging baskets.

Moonflower

The white morning-glory flowers of moonflower (Ipomoea alba) appear to glow at night when its luscious sweet scent attracts pollinators. The blooms of this annual vine open in the evening and close each morning. Grow in full sun.

Petunia

Grow old-fashioned varieties of petunias (Petunia selections) for a spicy, clove-like scent. The funnel-shaped flowers come in many sizes and color patterns.