In the world of horticulture, avid gardeners continuously assess the influence of genetics versus environment, as we examine a plant’s performance in our garden and in those of our far-flung friends. This past week, as I was visiting my friend Dan in Charlottesville, Va., I was reminded that perhaps not all plants are created equal, even when they are the same species.
Of course, we realize this when we grow varieties of plants that have been bred or selected by humankind to have specific traits, a point underscored by the range of tomatoes or other vegetable varieties that we have in our gardens. We have selected these plants over the ages and preserved their traits by isolating them and stabilizing their genes so that each seed will produce a ‘Brandywine’ tomato or in the case of ornamentals, a grape-toned flower like that of ‘Lauren’s Grape’ opium poppy. The genetic code of these plants and their seeds determine the traits that we value – the shape of the tomato, the color of the flower.
Sometimes a plant in the wild has a form that appears to differentiate it from other members of its species. What I wanted to determine when I spied a three-foot tall form of butterfly weed at the edge of Dan’s terrace was whether this difference was genetic or situational. Asclepias tuberosa is as appealing to me as it is to butterflies, which love the nectar from its bright orange flowers. For me, it’s the plant’s flower color and form that I like.
With that color in mind, I once added large numbers of this beloved native to a border that paralleled the driveway at my old house. Even though they had the same distinctive leaves and flowers that I saw in Virginia, my plants, which seeded themselves amongst the baptisias and shrubs that lined my old drive, were short in stature, never gaining a height of more than about eighteen inches. In my garden, they had the height of front-of-border plants. When I saw this taller form, I was so intrigued by the variable nature of this species I thought I knew well that I asked Dan to save me some of the seedpods from his plant once they matured. I wanted to grow them on. However, this left me wondering why did the plant took on such a different scale in his garden than in mine. And the answer is not obvious.
Since that sighting, I have been researching the species, asking friends about their experience with this plant. Some talked about the tall, red-flowered form grown at Chantcleer Garden in Pennsylvania; some talked about plants ranging in height from two to three feet; all talked about plants that were taller than the ones I had grown. While these variations were interesting, they did not provide me with the answer to the age-old question: why did these plants of the same species grow so differently? Was it genetics or environment? In plant terms, the manner in which a plant responds to its environment is known as its phenotype. In the case of this Virginia form of butterfly weed, which Dan said took on such height throughout the area, phenotypic conditions could include a longer southern growing season, competition from other plants that trigger the plant to grow taller to compete for sun, or nutrients in the soil that encourage more growth. Such conditions can greatly influence what a plant looks like, just as what we eat can influence our appearance (and our subsequent health).
At the same time, I couldn’t rule out the possibility that the cause of this plant’s characteristics were genetic, that I was looking at a genotype, not a phenotype. Over the years, I have seen evidence of both forms of influence. Understanding how environment impacts a plant can make one a better gardener. I can influence the flowering of a dogwood or clematis by placing it in a site out of full sun. This often lessens flowering, a quality I prefer. (I like a lighter bloom set, as it can seem more natural and subdued.)
In the case of hydrangeas, soil acidity, an external factor, can change the color of its flowers from pink to blue, depending on the whether the soil leans acid or alkaline. But sometimes it is unclear whether genes or environment are causing the desired (or undesired) quality. On the roads of Virginia, I also saw a stand of a native meadow rue that had a much fuller form than the specimens I first saw in my friend George Schoellkopf’s garden in Connecticut twenty years ago. In his garden the plant was slender and almost transparent, holding its pale green flowers on long stalks well above foliage that had the weightlessness of a maidenhair fern, but the form I saw along the roadside had full, lush foliage with tighter, more closely held clusters of flowers, a quality that could be put to good use in a garden.
Just as with Dan’s butterfly weed, there was only one way for me to determine what was the cause of this form: to collect its seeds and to grow it in varied conditions to see which traits might be inborn and which are a product of the environment. If the qualities persist in varied situations, this genotype might warrant collecting and saving so that I can use its traits to advantage in the garden. And if the qualities do not persist, perhaps I can approximate its growing conditions to see if I can create the desired effect. Whatever the result, I will have more knowledge of the plant, its inherent traits and how I want to grow it. Either way, the information I gather will make me a better gardener – and given that the information will not change my genetic make-up, I guess it will teach me about the conditions required for me to grow in the best possible way as well.
A gardener grows through observation, experimentation, and learning from the failures, triumphs, and hard work of oneself and others. In this sense, all gardeners are self-taught, while at the same time intrinsically connected to a tradition and a community that finds satisfaction through working the soil and sharing their experiences with one another. This column explores those relationships and how we learn about the world around us from plants and our fellow gardeners.