Those who read this column regularly are probably aware of the rivalry between my colleague, Brent Green and myself. I have always been involved in the agricultural/horticultural production industries. If I was to landscape my garden, it would probably resemble row crops with an orchard. Brent, however, is a landscaper and enjoys design. His garden is much too elaborate for my taste. In fact, if you were to ask me, I would say that his garden stinks. I mean that quite literally; as there is an overabundance of fragrant flowers and foliage which can be overwhelming on warm and humid days.

Perennial plant species with fragrant or “aromatic” foliage, such as sage, rosemary and thyme (and according to Simon and Garfunkel, parsley) are often used specifically for their fragrance and many are culinary herbs. Incense cedar, camphor, cypress, eucalyptus and pine are examples of some of the trees which exhibit aromatic foliage. Juniper, lavender and myrtle may be used as aromatic shrubbery. Brent suggests using such species close to walkways or traffic areas where they can be appreciated. The fragrance of most is more noticeable if the plants are brushed against by visitors to the garden. Brent has even planted sage behind a gate where it is struck when the gate is opened.

Fragrance in flowers is as variable as the plants which produce them. Generally, if a flower is fragrant, it is trying to attract a vector which pollinates it. Although many plant species have several potential vectors, each has a “vector of choice” which it tries to be most appealing to. Flowers which primarily attract bees are usually more profuse and often mildly fragrant. Strongly sweet fragrance from fewer flowers is usually employed to attract bats. This is why such flowers are most noticeable on warm evening. Many plants species are endemic to areas with different vectors which are not present here. However, they continue to produce the fragrance which was so effective back home. (It is kind of sad if you think about it.) There would not be such variability in fragrance if all flowers were designed to attract the same vector.

Incidentally, there a few flowers which are pollinated by flies, (generally in the family Araceae.) They produce fragrances attractive to flies, which are not so appealing to people. Anyone who has grown a voodoo lily is already aware of this. Fortunately, most fly pollinated species are grown for their foliage and the flowers may be removed before they open. The most common plants from this family are philodendrons, which are usually maintained in their juvenile state, consequently unable to bloom.

Because aromatic flowers are designed for their vectors, they also try to bloom when the vectors are most active. Those which use insect vectors usually bloom after there has already been some degree of warm weather. Earlier blooms can not be serviced if the vectors are still dormant or pupating. The same warm temperatures which stimulate activity among insects also stimulate increased fragrance in flowers. (Humidity also enhances fragrance.) Flowers which prefer bats may stop producing fragrance and even close their petals during the day while bats are resting. Many cactus produce flowers which are open all night for bats and moths. Some cactus even engage in rather creative advertising. Their translucent petals reflect ambient moon and star light which guides moths to the source of the fragrance.