Color Change in Plant Displays
If you planted a garden expecting vibrant flower colors but noticed a dull appearance during this drought year, don't blame yourself or the catalog photos. The issue may lie in the environment's impact on your plants. Let’s explore this phenomenon and uncover what’s happening!
Why are my client’s flowers different from the catalog picture?
How Environmental Stressors Change Plant Display
If you were planting a garden with lots of flower color and suddenly, this drought year, everything looked lackluster, it’s not you or even the catalog picture that’s the issue. It could be the environment affecting your planting. Flower and leaf color are a direct result of environmental conditions. In times of high stress, flower colors can change or exhibit unusual characteristics.
The Problem
As erratic weather patterns become commonplace and we have wide distributions of plants found or bred in one area and growing in another, changes in floral display can be expected as plants face new challenges and stressors. What is stressful to a plant? What do you mean it won’t look like the picture? Let’s dig into this phenomenon and figure out what’s going on.
Some Factors that Affect a Plant’s Appearance
- High heat during the growing season
- Transplant shock
- Age of the flower or the overall plant - color fades as a flower ages
- High humidity all day and continuing through the night (i.e. no rest period for the plant’s respiration)
- Inconsistent soil moisture
- Soil pH changes
- Ozone levels and UV exposure
- Bred or selected in one location and growing in another location
At first glance, this color variation can be chalked up to variability in the species. But the message boards of flower farmers show that they’ve been taking notes of this abnormality for quite some time. (And why wouldn’t they be, picture-perfect flowers are their livelihood.)
In hot and dry areas, stressed plants don’t flower like plants with more moderate temperatures, consistent soil moisture, and cooler nighttime temperatures with lower humidity. Annual cut flower zinnias are notorious for this in the cut flower farm world. While the seed catalog may show the newest double-flower cultivar to be one vivacious color when grown in lush, cool Oregon, in Texas, it’s washed out and faded, without the interesting double-petal count. As you might expect, environmental stress affects how a plant behaves. Goodness, it affects how we behave, and we can go inside. And it’s not just ornamental flowers that feel the strain. In the native perennial world, two common native plants that people notice change in flower color are Allium cernuum (nodding onion) and Echinacea purpurea (purple coneflower). Allium cernuum is known for blooming a darker pink in cooler parts of its native range and is found to be a light pink-white in hot and humid climates. Echinacea purpurea color saturation is different through the growing season, soft pink in the heat and humidity of summer but turning magenta when sporadic rebloom happens in the cooling fall. Why does this happen?
Flower color is the visible result of a complex process involving the metabolic protein pathways to produce pigments- carotenoids for yellows to orange hues and anthocyanins for blue reds to pinks to purples. As we may remember from our school days, temperatures affect protein synthesis and enzyme stability. Enzymes are a type of protein. Their presence or absence triggers different reactions resulting in a range of hues. However, in periods of environmental stress, the signals for certain enzymes and proteins to be produced and at what amounts change. Cooler temperatures usually trigger more anthocyanin enzymes while warmer temperatures favor carotenoids resulting in more reds and purples in cool temperatures and more yellows and oranges in warm ones. However, lighter coloring is more than just faded pigment. In flowers with exposed pollen anthers or stigma, the lighter flower color reflects the strong UV light and reduces heat around the sensitive reproductive organs to mitigate heat and provide protection. On the other hand, when temperatures are very hot, especially at night when plants respire, color production slows or stops altogether because the plants can’t synthesize its color pigments which results in faded colors or white shades. In high exposure to light or temperatures, cell walls break down, leaching color and leading to phenomenon of sunscald where plants have white or yellowed foliage or flowers as plant material is damaged from environmental stress.
Plant breeding adds another layer of complexity to the equation. At the turn of the 20th century, North American native plants weren’t as popular as garden plants in the US and Canada, but the plants were fascinating to gardeners and plant breeders in Europe. In Germany, the Netherlands, and England, plant breeders worked diligently on selecting forms and colors of North American plant species to improve their performance in the European garden. These selections, such as Rudbeckia ‘Goldsturm’ or Helenium ‘Moerheim Beauty’ are wonderful, compact, and colorful perennials, well-loved in both American and European gardens. However, most of northern mainland Europe and southern England have a much milder climate than the locations where these plants originated in North America. Here in the Mid-Atlantic, we frequently have high humidity and temperatures in the 90s through July and August and winters below 0, both extremes very uncommon in more mild European locations. As a result, the complex coloring of the flowers and the health and vigor of European-selected North American cultivars perform best when given conditions closer to the climatic conditions they were selected in, something to keep in mind for North American gardens. It’s not that these plants won’t grow in the average American garden, it’s just that it may not look exactly as pictured.
The Fix
While we can’t change the weather, knowing what we can alter goes a long way to setting customer expectations. No matter our intentions, variability in the floral display is inevitable and we can’t control what the weather is doing.
With that in mind, decide your objective and work back from that. If the client is going for a more self-sufficient landscape ideal, it's important to communicate with clients that color changes are a natural response to environmental conditions. Having your information at hand helps you better educate clients on what to expect from their planting and the changes it will pass through from season to season and year to year. The first season after a plant installation will be singular in its display. Transplant shock and the stress of adapting to a new environment will trigger one-off behaviors in the plants as they struggle to put down roots. Flowers may bloom too early, not be the color you expected, or the habit isn’t as described - keep the faith. The first growing season is one of the strangest and isn’t necessarily representative of how the plant will look in future seasons. Eventually, planting material will settle in, and the floral display will find its rhythm for the environment and location. Flower colors may be lighter or darker, bloom for a longer or shorter window - variabilities that depend on the site.
If the client’s aim is a brilliant bloom display akin to the catalog photo, it is best to shoot for peak overall plant health. Getting great flowers is the result of consistent soil moisture, appropriate soil nutrition, and gentle light exposure. Avoid extremes like extreme heat, drought, UV exposure, and nutrient deficiency, and shoot for optimal plant performance. While the genetics of a plant is the largest determining factor in how its flower color will display, giving a plant its ideal conditions will result in the best flower color or flower forms. Beloved features of cultivated selections such as the sought-after quilled petals in Rudbeckia ‘Henry Eilers’, double-flower forms in Echinacea cultivars, the deep foliage and flower coloring of Heliopsis cultivars, or a pink hue in Oenothera speciosa happen when all a plant's needs are met. In plants with large native ranges, having an approximate idea of where your client’s garden is in the plant’s native range and adjusting light exposure and soil moisture based on where they are will yield the greatest floral display. If your client is located in Georgia and the plant’s southernmost range ends in Georgia, you’re at the plant’s top limit of heat and humidity tolerance. Give that plant some light afternoon shade and more soil moisture. However, if the client is in Maine, the same plant will display best in full sun and tolerate drier soils. When a plant is at its extreme, it reverts to less resource-intensive forms like single flowers, shorter habits, less leaf variegation, and desaturation of flower colors.
Plants are tough and durable, but the best flowers come from when a plant is thriving, not just surviving. Not everyone is looking for picture perfect flowers and some folks want to match the energy of the site. To these folks, we say lean into what’s happening and educate clients why the plant may behave unexpectedly this season or the next. For those who have stricter aesthetic requirements, providing additional resources to the plants and situating them carefully for optimal health may be necessary to deliver a photo finish. While there’s not much one can do about the weather, choosing the right plant for the conditions will go a long way to getting the most from a display.
Learn More:
Gardening Simplified. Why Flower Color Fades in Summer. 7 September 2022.
Sullivan CN, Koski MH. The effects of climate change on floral anthocyanin polymorphisms. Proc Biol Sci. 2021 Mar 10;288(1946):20202693. doi: 10.1098/rspb.2020.2693. Epub 2021 Mar 3. PMID: 33653138; PMCID: PMC7935138.
University of Utah. The Genetics of Flower Color.
In Defense of Plants. Floral Pigments in a Changing World. 7 October 2020
Aridi, R. Flowers Are Changing Color in Response to Climate Change. Smithsonian Magazine. 2 October 2020.
The Kokoro Garden. Why Your Cupcake Zinnias Aren't Cupcake-Shaped. 26 August 2019.
