The Many-Splendored Scents of Herbs
I am often asked how is it possible that herbs come in so many disorienting scents and flavours such as basils in unlikely lime, lemon and camphor versions, geraniums in orange, rose and coconut, and mints overstepping boundaries in lemon, ginger and banana varieties. Did somebody take genes from a banana and combine them with a mint plant? With these and many other scented oddities it is easy to see why people might think that something is amiss in the herb patch, whispers even of herbal GMOs foisted on the gardening public!
Let me reassure you that none of these herbs are GMOs, or genetically modified organisms. They truly are Mother Nature’s gifts and we humans only need to find them and grow them. It’s like a treasure hunt, and plantspeople, like everybody else, love to find a treasure.
Part of the puzzle is rooted in how we think about scents such as "lemon", "lime" and "rose". We all automatically associate these scents with the classic sources: the lemon from the lemon tree, the lime from the lime tree, and the rose flower from the rose bush. The surprise is that Mother Nature did not give these plants a monopoly on their signature scents and flavours. In fact, the way that Mother Nature designed things, these scents were destined to reappear elsewhere in the plant world.
It helps to understand a little about the olfactory phenomenon at work that gives rise to the sensation of scents. Scented plants are rich in essential oils. When the leaves of these plants are rubbed or when a flower opens these oils are released to the air. A chemist would call these oils "volatile", not because of any pugilistic tendencies, but because the oils are so lightweight they vapourise readily at room temperatures. Once in the air, the essential oil molecules migrate to our noses, attach themselves to receptors lining our nasal passages, triggering a series of neural pulses that our brains are conditioned to process as the "lemon" scent or the "rose" scent.
A similar process is at work when you taste these herbs: the same essential oils migrate up the nasal passages from the mouth and together with signals from the tastebuds, the nasal sensors contribute to a package of pulses that our brains have learned process as taste. It turns out that the nose plays a big part in the sensation of taste. That’s why people who have no sense of smell also have an impaired ability to taste foods.
Now, the key to understanding why no plant has a monopoly on any scent is to know that essential oils are not made up of a single substance of uniform molecular composition. With few exceptions most essential oils responsible for scent and flavour are a mixture of component chemicals that together generate the specific neural pulses that are we call "lemon", "orange" or "banana" by convention. It is these component chemicals that reappear over and over again throughout the plant world.
Let’s take the essential oil of lemon as an example. It is composed of many individual component chemicals. The major ones are a-pinene, camphene, b-pinene, sabinene, myrcene, a-terpinene, linalool, b-bisabolene, limonene, trans-a-bergamotene, nerol and neral. How much of each of these chemicals is manufactured by the lemon tree is controlled by the plant’s genes. Orange oil has most of the same component chemicals, but in different proportions, controlled of course by its unique collection of genes. Lime oil too has many of the same components but again in different proportions.
Now let’s look at one of the imposter lemon herbs, lemon verbena. Anyone who has had the pleasure of taking in the intoxicating scent of fresh lemon verbena leaves knows that it has the unmistakable character of lemon, but it is definitely not the same as lemon. I regard the scent and flavour of lemon verbena as a major refinement on the best that the lemon tree can produce. It’s a sort of olfactory one-upmanship that makes the herbal world so endearing to many of us. To my nose, there is a regal exuberance in lemon verbena that is missing in lemon oil, as if Mother Nature decided to fill in the gaps after its first try at creating the lemon scent.
Lemon verbena oil’s major components are borneol, geraniol, linalool, nerol, citral, dipentene, limonene and myrcene, some of which are major components of lemon oil or chemically close to the components of lemon oil. Geraniol, which is also found scented geraniums, basils and others, is similar to geranyl acetate found in lime oil. Lime oil also has borneol and citral found in lemon verbena but not in lemon oil. The picture that emerges is that the different scents are like hands dealt from a deck of cards, and sometimes you get god-awful combinations such as the herb cat thyme (Teucrium marum) which is unblessed with (or blessed with if you are a cat) a horrible scent to humans.
Through sexual reproduction genes are shuffled every time a seed is produced, a fact that plant breeders have taken advantage of for millennia. Plants grown from seeds collected from a mother plant may have differences that are too slight to notice. But often the genetic differences are very noticeable, and breeders will select out the plants that catch their fancy and develop them as new varieties. This is exactly the process I used when I developed Richters’ Orange Spiceš thyme in 1995. Out of about a hundred seedlings in a test seed box, I discovered two that had the incredible scent and flavour of fresh orange peels, quite unlike other orange-scented herbs such as ‘Orange Balsam’ thyme and ‘Prince of Orange’ geranium. The two seedlings even differed from the classic orange oil scent, which actually does not have much of the "peel" note you get when you grate fresh orange peel. From those two seedlings millions of identical plants have been produced by cuttings and division, and now Orange Spice thyme is one of Richters’ all time (thyme?) best selling herbs. Besides its unique scent, it is a terrific ground cover herb, forming dense mats no more than 2-3 inches high, and is perfectly hardy in Southern Ontario.
This process of selecting out new plants with desirable characteristics is something any observant herb gardener can do - no special equipment or training is necessary. Over the years, Richters has introduced a number of spectacular new herbs originally obtained from amateur herb gardeners. Finding a new scented herb requires only a functioning nose. I encourage anyone who thinks they have found something new in their gardens to contact me. Who knows, it may be worth a few cents too.