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Growing Green: Fascinating fragrances

From Victorian pocket melons to Thomas Jefferson's prized scented geraniums, fragrances have been a part of human culture for a very long time.

Flowers have been shown to have positive effects on human emotions, and recent research has shown that fragrant flowers are a positive emotion inducer. This should come as no surprise to most gardeners.

Breeding improvements in flowers have rarely included fragrance characteristics, which were considered to have a negative effect on vase life. Recent studies on fragrance suggest that this might not be the case, and researchers at David Austin Roses are making progress in improving the vase life of fragrant roses.

Fragrance provides a vital service for the plant. A plant's distinct aroma attracts pollinators, thereby facilitating cross-pollination and the continuation of the species.

For example, plants pollinated by moths produce optimum fragrance in the evening, as moths are nocturnal. Thus Nicotiana alata (flowering tobacco) is more fragrant at night, when moth pollinators are out and about.

Plants pollinated by bees produce optimum fragrance during the day, as bees are diurnal. Thus Antirrhinum majus (snapdragon) is more fragrant during the day, when bee pollinators are likely to be active.

Different but specific fragrances also help to ensure that insects visit flowers of a similar species, increasing the potential for successful cross-pollination. From a long distance, flower fragrances are more effective than visual signals in attracting a pollinator, especially to small or hidden flowers.

Flower fragrances tend to be at their highs when they have sufficient nutrition. In addition, moderate to warm temperatures and high light tend to increase fragrances.

Time of day can also affect the strength of a flower's scent. Therefore, gathering flowers at the appropriate time and season will maximize the flower's vase fragrance.

For instance, roses should be picked at night when they are at their most fragrant, whereas jasmine flowers are harvested when their fragrance is at its peak just before dawn.

To extend your garden's fragrance window, why not grow the nectar plants that pollinators on the night shift prefer. Good candidates for moths include:

Night Gladiolus (Gladiolus tristus) has creamy yellow blossoms that have an intense spicy fragrance at night.

Pinks (Dianthus plumarius): The pale pink flowers have a rich clove scent.

Evening primrose (Oenothera): With sweetly scented blossoms of soft white, pink and bright yellow that open in the evening.

Moonflowers (Ipomoea alba): This night-blooming relative of the morning glory perfumes the garden as its large five- to six-inch white flowers open at dusk. A quick-growing climber with large heart-shaped leaves.

Evening stock (Matthiola incana): Small pink or purplish flowers are not showy but emit an intoxicating fragrance at night. Grows to one foot with lance-shaped leaves.

Four O'Clocks (Mirabilis jalapa): Sweetly fragrant and colorful trumpet-shaped flowers, open in late afternoon releasing a jasmine-like perfume. Found in the gardens of Thomas Jefferson at Monticello, the bushy plants grow 24 inches tall and are an annual in our climate.

Daylilies: There are many daylilies that bloom at night, including moon frolic and Toltec sundial.

For more information about night-blooming plants, visit www.coopext. or www.weekendgardener.