One of the best parts about going to plant sales and setting up a booth is that you get to hear everyone’s story about their favorite plants that you may or may not be selling. Seeing people enthusiastic to learn and share plant knowledge refills my inner reservoir of hope. We participated in the Hall County Master Gardener’s Fall Expo last weekend and talked to some wonderful people (many of whom were Hall Co. Master Gardeners, y’all were awesome!) and sold a bunch of plants. One exchange in particular made me incredibly happy because I finally heard someone express the concept I’ve been trying to convey to anyone that will listen for years: Leaves on a perennial plant (especially in fall ) are expendable and don not necessarily reflect the overall health of the plant.
I was talking to a couple as they browsed our plants, and as the wife decided she would like a Giant Hyssop (Agastache scrophularifolia) she picked up two pots and started comparing the plants in them. She asked her husband, “Which one?” He responded that they looked about the same. She expressed concern about the yellowing leaves on one of the plants, but it had more stems, so she kind of wanted it more. He turned to me and asked “It’s perennial, right?” I said that it was with a nod. He said “Well, then you’re buying the roots. Those leaves are going to be gone in a few weeks anyway.” I think I just found my new best friend. I’m pretty sure I saw the wife roll her eyes and then select the plant with 2 stems.
Leaves on a perennial plant go through an annual life cycle that eventually ends with them shutting down and dying. This is known as ‘leaf senescence’ and most people know it more commonly as “when the leaves change color in Autumn.” This cycle was summed up incredibly well in a paper about the molecular causes of leaf senescence that I came across:
“Leaves initiate their life as leaf primodia. During their development and growth, they become photosynthetically competent and accumulate nutrients. Leaves then enter the senescence stage, followed by their death. Leaf senescence partly involves the process of ‘wear and tear’ during aging, but mostly is a tightly regulated process with a crucial biological purpose.” – http://jcs.biologists.org/content/126/21/4823
Leaves are formed, perform their function of collecting solar energy to build roots, stems, more leaves and flowers, and then are systematically dismantled and their components are resorbed and redistributed to other parts of the plant. The remaining framework is then dropped to the soil, most likely to be reabsorbed by the roots after passing through the soil food web.
In this context, looking for the leaves to be green and healthy on a plant in October seems a bit absurd. Plants that bloom in spring usually shut down in the summer heat, and the ones that bloom in fall are sending all their resources to make flowers and then seeds before a frost comes along. Another quote from the aforementioned paper again sums it up well:
“The blooming of spring flowers occurs through the utilization of nutrients that have been relocated from senescing autumn leaves. Thus, senescence and death in leaves are active developmental strategies that crucially contribute to the fitness and survival of a plant.” –ibid
Just look at this beautiful Georgia Aster bloom:
Now take a look at the leaves closer to the base of the stem:
Not nearly as aesthetically appealing as the flower, but part of a totally necessary and natural process on a healthy plant.
Fall is the best time to plant perennials, so now is the time to shop at one of the many plant sales going on in the next few weeks. If you see some less than perfect leaves, don’t worry. They won’t be there much longer. They too shall pass, and in doing so enable the roots to survive the winter.