Why White Dahlias Don’t Always Stay White: A Science-Based Guide for Growers and Breeders

Copyright © 2025 by Steve K Lloyd
All Rights Reserved

Cover Image: Dahlia ‘Yuukyu’ grown in Virginia (USA). Photo courtesy of Kraus Farm. Used by permission. (Author’s image file 143-1)

What makes some dahlias bloom in clean, crisp white—while others blush pink in the sun, yellow with age, or produce flowers that shift unpredictably from year to year? For dahlia lovers and breeders, white blooms can be among the most elusive and confounding.

White is one of the most sought-after and most fragile colors in dahlia breeding—revered for its purity but often prone to surprising changes.

In this article, I’ll explain what causes white coloration, what disrupts it, and how you—as a grower or hybridizer—can better understand and work with the genetic and environmental factors that influence white dahlia blooms.

Dahlia ‘Colwood Hope’ grown in Washington State (USA). Photo courtesy of Good Life Dahlias. Used by permission. (Author’s image file 113-1)

My goal is to make complex flower chemistry accessible without sacrificing scientific accuracy.

Based on nearly a dozen published, peer-reviewed studies and over a century of flower color research, this deep dive into white dahlias combines what scientists have uncovered with real-world insights for dahlia growers, hybridizers, and anyone interested in the science of dahlias.

At first glance, white may seem like the “default” bloom color—a lack of pigment, like a blank canvas waiting for the artist to begin applying glorious color. But in dahlias, achieving a white appearance is surprisingly complex.

Dahlia ‘White Love’ grown in Palmerston North in the Manawatu region on the north island of New Zealand. Photo courtesy of Wainee Soo via Facebook. Used by permission. (Author’s image file B-1)

Some dahlias appear white simply because they lack the red, purple, and blue pigments known as anthocyanins—the same ones found in roses and blueberries. Others take on a pale yellow, ivory, or cream hue due to small amounts of other pigments: soft yellow flavones, bright orange carotenoids like those in carrots and marigolds, or golden anthochlor pigments such as chalcones and aurones..

Still others reflect light in ways that appear white to the human eye, even if microscopic pigments are present.

Dahlia ‘Korb River Bend Jean’ grown in southeast Michigan (USA). Photo courtesy of Lucas Schmersey via Facebook. Used by permission. (Author’s image file 123-1)

A weak or absent yellow base may be part of what allows white coloration to show clearly. Scientists have found that in some dahlia cultivars, pale flavones are produced instead of stronger anthocyanins, resulting in blooms that appear white or faintly yellow.

It’s a little like the difference between freshly fallen snow and densely packed glacial ice—both are made of the same substance (water), but they reflect and absorb light differently, producing very different visual effects.

The interaction of light with petal tissues, pH, and co-pigments such as flavonols can subtly shift how ‘white’ appears to our eyes—creating warmth or coolness without a major pigment shift.

This diagram shows how pigment production can be blocked after genes are transcribed.
In some white dahlias, small interfering RNAs (siRNAs) attach to messenger RNA (mRNA) before it can be used to make pigment enzymes. This prevents color from developing—even when the pigment genes themselves are perfectly normal.

Importantly, a white flower may still produce pigments at the biochemical level—but these may be colorless, masked by other compounds, or deposited in low enough quantities to appear white

Dahlia ‘Blizzard’ photographed in Kansas City (USA) on 27 August. The grower notes “Stays bright white all season for me, both in my tunnel and the field. My favorite white dahlia.” Photo courtesy of Melissa Ginther. Used by permission. (Author’s image file 105-5)

One of the most frustrating traits for growers and breeders is the way white dahlias sometimes fail to stay white. A plant that bloomed pure white last year might blush pink this year—or display yellow tints along the base of the ray florets (the structures commonly called petals).

Sometimes, these changes are transient: a cultivar might bloom white in cool spring weather and shift pink in midsummer heat.

This kind of reversion has been observed for nearly a century; W.J.C. Lawrence (1935) documented cultivars where pale blooms frequently darkened under summer heat or shifted back to white when cooler conditions returned.

Dahlia ‘Rogue Starburst’ early in the season, and late in the season when it shows distinct blush tones. Grown in Sterling Heights, Michigan (USA). Both photos courtesy of Jinah Kim via Facebook. Used by permission. (Author’s image files 130-4; 130-2)

Modern studies show that heat and UV light don’t just fade pigment—they can actually change which pigment genes are active. For example, heat can suppress genes that make red or purple pigments, while activating genes for pale yellow tones.

Dahlia ‘Fleurel’ grown in Lancashire, northwest England. Photo courtesy of Krisztina Fodor via Facebook. Used by permission. (Author’s image file 118-4)

Dahlia ‘Fleurel’ photographed in northern Alabama (USA) in September. Photo courtesy of Stacey Carmichael via Facebook. Used by permission. (Author’s image file 118-7)

The popular variety ‘Café au Lait’ is a well-known example. Though widely grown as a white dahlia, it more often blooms beige, blush, or faded lilac—and rarely blooms consistently white.

Dahlia ‘Café au Lait’ photographed in the author’s Anacortes, Washington (USA) garden on 18 August. Photo by the author. (Author’s image file C-1)

In other cultivars, pigmentation can vary from bloom to bloom on the same plant, or even across different ray florets (petals) of the same bloom. In some cases, this irregular pigmentation results from floral chimeras—where genetically distinct layers in the flower give rise to differently pigmented tissues.

Environmental factors like temperature, sunlight, and soil chemistry can all play a role. So can underlying genetics, somatic mutations, and even virus infection.

This four-panel graphic illustrates why white dahlias don’t always stay white:
• Environmental Shifts – Heat and sunlight can activate pigment production in blooms that were previously white.
• Genetic Pathways – Pigments like anthocyanins and flavones are made—or suppressed—based on enzyme activity regulated by specific genes.
• Reversions – Some white dahlias revert to colored forms due to unstable mutations or environmental stress.
• Chimerism – A single bloom may show both white and colored areas due to layers of genetically different tissue.

Together, these factors make white one of the most delicate and unpredictable flower colors in dahlia breeding.

Dahlia “Bonesta’ photographed in the author’s garden. This bloom is an example of chimerism. Photo by the author.

Color in dahlia ray florets is controlled by a family of genes that regulate pigment production. The most important pigment groups in dahlia ray florets are:

1. Anthocyanins – pigments that create red, purple, and blue coloration
   
   

2. Flavones – pale yellow to nearly colorless pigments that can dilute stronger colors
   
   

3. Chalcones and aurones – bright yellow pigments responsible for golden hues in many cultivars

At the heart of this system is chalcone synthase (CHS)—an enzyme that catalyzes the first step in the flavonoid pigment pathway.

CHS suppression is a common genetic mechanism in white dahlias, halting anthocyanin production at the very first step. This has been confirmed across multiple cultivars through RNA sequencing and gene silencing studies.

This diagram shows the flavonoid biosynthesis pathway in dahlias.
At the center is CHS (Chalcone Synthase), the enzyme that kickstarts pigment production. When CHS is suppressed, the process stalls. In many white dahlias, another enzyme— FNS II (Flavone Synthase II)—is more active, diverting pigment precursors toward pale yellow flavones instead of colorful anthocyanins or golden chalcones and aurones. This shift in pathway activity helps explain why some white dahlias stay pure, while others develop unexpected color.

If CHS is suppressed or disrupted, pigment production stalls, and the bloom may appear white. In many white cultivars, flavone synthase II (FNS II) is simultaneously upregulated—redirecting precursors away from anthocyanins and into pale yellow flavone pigments.

In one influential Japanese study, the cultivar ‘Yuino’ was shown to produce white ray florets in part because of this shift in enzyme activity. In some dahlias, this suppression is controlled by small interfering RNAs (siRNAs)—molecules that interfere with gene activity after DNA has already been transcribed into RNA.

Dahlia ‘Yuukyu’ grown in Sterling Heights, Michigan (USA). Photo courtesy of Jinah Kim via Facebook. Used by permission. (Author’s image file 143-3)

This suppression often works through a process called post-transcriptional gene silencing—where small RNA molecules intercept pigment instructions before they can be used by the plant.

Genetics alone don’t determine whether a dahlia will bloom white. The plant’s environment can heavily influence gene expression and pigment production, causing blooms from the same cultivar to flower differently depending on where and how they are grown.

Cooler temperatures tend to favor anthocyanin production, while heat can suppress these pigments. This is one reason why white dahlias may remain pure in cool climates but blush pink or lavender in warmer conditions.

Dahlia ‘Beaucon White’ grown in Washington State (USA). Photo courtesy of Denise Lakin via Facebook. Used by permission. (Author’s image file 104-2)

Dahlia ‘Beaucon White’ grown in southeast Michigan (USA). Photo courtesy of Jessica O’Hara via Facebook. Used by permission. (Author’s image file 104-1)

Soil nutrient imbalances—particularly of nitrogen, phosphorus, or potassium—can also influence how and when pigment precursors are formed. These changes are subtle, but they help explain why some white dahlias seem to “blush” in certain locations or seasons and not in others.

While current research doesn’t specify which nutrient ratios most affect white cultivars, many growers suspect that higher nitrogen or phosphorus levels may tip the balance. It’s an area still under investigation—and a good reason to observe how your own plants respond to different soil and fertilizer regimens.

Light exposure also matters. Studies show that plants grown in full sun tend to produce more pigment than those receiving only partial sunlight. Thus, two plants with identical genetics may bloom differently depending on how much sunlight they receive in different parts of the garden.

White coloration in dahlias is sometimes caused by somatic mutations—spontaneous changes in individual cells that can affect an entire bloom, a single ray floret (petal) or one growing shoot.

In the cultivar ‘Yuino’, white and pink ray floret areas were found to result from cell-specific differences in CHS gene expression. The same plant can produce pink, white, or striped ray florets depending on where the mutation occurs.

A first-year, open-pollinated seedling in the author’s garden late in the 2023 growing season. It was unfortunately lost before I could grow it a second year. (Author’s photo)

Because somatic mutations aren’t passed through seed, the only way to propagate them is vegetatively—through tuber division or cuttings, both of which preserve the plant’s exact genetic makeup. But this comes with risk: such mutations are often unstable. A bloom that is white one year may revert to color the next.

This helps explain why some “white sports” of colored dahlias—accidental branches that produce white blooms—don’t stay white for long, or only do so under very specific growing conditions.

Even when a dahlia carries the genetic machinery for white blooms, that trait can be surprisingly easy to disrupt. Virus infections, genetic instability, and environmental changes all contribute to color variability.

Some prized white cultivars—‘White Nettie’ and ‘White Perfection’, for example—have shown susceptibility to petal discoloration. In some cases, virus infection may be a factor, interfering with the plant’s ability to regulate pigment genes after they’ve been transcribed from DNA into RNA. In others, transposons or unstable mutations may be at work. 

While viruses are not the most common cause of pigment shifts in white dahlias, they’re one of several biological disruptions that can make color less predictable. (They’ve played a more central role in the story of black dahlias—a topic I explore in this related article.)

Dahlia ‘White Nettie’ grown in Washington State (USA). The grower notes “Some years it seems like this one throws more yellow, some years it looks more white. This last season it had more yellow hints.” Photo courtesy of Denise Lakin via Facebok. Used by permission. (Author’s image file 140-5)

Dahlia ‘White Perfection’ grown in Leicester, England. The grower notes that the blooms stayed white all season. Photo courtesy of Alexa Fears via Facebook. Used by permission. (Author’s image file 141-1)

Environmental triggers such as UV exposure, high temperatures, and nutrient imbalances can all increase the odds of pigment production in plants genetically predisposed to white coloration—but not genetically locked into it.

In essence, white dahlia blooms exist on a razor’s edge—requiring the right balance of gene activity, stable cell development, and environmental harmony to remain white.

If you're growing popular white cultivars such as the ones illustrated in this article—or any of the hundreds of other popular white dahlias—consider documenting their bloom colors throughout the season. Track changes over time, note weather patterns, and share images with growers in other regions.

A coordinated project involving growers from varied climates—Washington, Southern California, the Midwest, New England, and the Deep South—could yield insights far beyond what any single lab study can provide. 

Comparison between matching cultivars grown in the Northern and Southern hemispheres, and at markedly varying altitude, could be even more revealing.

Dahlia ‘L’Ancresse’ photographed in New South Wales, Australia. Photo courtesy of Southern Highlands Flower Farm. Used by permission. (Author’s image file 124-2)

Dahlia L’Ancresse’ photographed in Washington State (USA). Photo courtesy of Idlewild Blooms. Used by permission. (Author’s image file 124-1)

Whether you’re aiming to stabilize color traits in a formal breeding program or simply hoping to raise clean, consistent white blooms from open-pollinated seed, understanding the science behind white dahlias can help you make more informed—and more successful—choices.

Select parent plants that bloom white across multiple seasons and conditions. If a plant shows frequent blush or revert-to-color tendencies, it may not carry genetically stable white coloration.

While you won’t have a lab to test enzyme levels, white seedlings that stay white under sun and heat are promising candidates. Discard those that show early pigment intrusion.

Grow white seedlings in various seasons or environments. Blooms that remain white in both cool and warm climates are more likely to have durable genetic traits.

Rather than harvesting seed immediately, propagate promising seedlings by dividing tubers or taking cuttings. This preserves the exact traits you observed and allows long-term evaluation.

Document what you grow. Over time, photos and notes will reveal which plants truly maintain white coloration—and under what conditions.

Dahlia ‘Bowen’ photographed in Washington State (USA). Photo courtesy of Idlewild Blooms. Used by permission. (Author’s image file 108-1)

Dahlia ‘Bowen’ photographed in New South Wales, Australia. Photo courtesy of Southern Highlands Flower Farm. Used by permission. (Author’s image file 108-2)

Even when a dahlia carries the genetic machinery for white blooms, that trait can be surprisingly easy to disrupt. Virus infections, genetic instability, and environmental changes all contribute to color variability.

Yet white isn’t merely an absence—it’s a highly regulated outcome. In dahlias, complex gene networks must actively suppress pigment synthesis, reroute precursors, or silence key enzymes.

Dahlia ‘Salish Snow Day’ grown in northern Illinois (USA) and photographed in late September. Photo courtesy of Darcy Dawson via Facebook. Used by permission. (Author’s image file 132-1)

Unlike in wild species where white petals may signal particular pollinators or adaptive traits, cultivated dahlias reflect breeder preference rather than evolutionary pressure—making instability more likely and more revealing.

Modern dahlias are complex hybrids descended from several wild species. This tangled ancestry means that hidden pigment traits can reappear generations later—even if they’ve been ‘silent’ for years.

If you’ve made it this far, you’re already ahead of the curve. Understanding the genetics behind white blooms isn’t just a curiosity—it’s a tool. It lets you notice patterns others might miss, test ideas in your own garden, and grow varieties that are not only beautiful but more stable year after year.

Breeding white dahlias may never be simple, but it becomes less mysterious with each season you observe, question, and experiment.

Dahlia ‘White Nettie’ and others grown in Missoula, Montana (USA) and photographed on 29 September. The grower notes “My dahlia garden is on a hillside that faces west. ‘White Nettie’ stays white all the way until frost.” Photo courtesy of Ryan MacPherson via Facebook. Used by permission. (Author’s image file 140-2)

As an example of the “strength in numbers” approach to expanding our shared knowledge of dahlias, I put out a call on social media asking growers to contribute photos of 42 white dahlia varieties. 

My goal was to show how blooms from the same cultivar can appear when grown in widely separated regions. To my delight, I was inundated with beautiful white dahlia photos within 24 hours of my ask.

Most of the images used in this article were generously contributed by dahlia growers across the United States, as well as the United Kingdom, Australia, and New Zealand.

Although I was able to include only a fraction of the submitted photos, I want to extend my appreciation to everyone who volunteered images to share with the worldwide dahlia community.

Special thanks to:

Emily Fontes of Idlewild Blooms in Stanwood, Washington, USA

Lindsay Kraus of Kraus Farm in Nokesville, Virginia, USA

Jen Foster of Southern Highlands Flower Farm in New South Wales, Australia

Anthocyanins – Red, purple, or blue plant pigments that contribute to flower color.

Anthochlor pigments – A group of yellow pigments including chalcones and aurones , distinct from carotenoids.

Biosynthetic pathway – A step-by-step chemical process by which plants create pigments.

CHS (Chalcone Synthase) – The first committed enzyme in the anthocyanin and flavonoid biosynthesis pathway.

Chimera / Chimerism – A plant composed of two or more genetically distinct cell lines. In dahlias, chimerism can result in blooms that are partly white and partly colored, depending on the genetic makeup of different tissue layers. The most stable form, known as a periclinal chimera, involves genetically distinct outer and inner layers, which may influence flower color or form.

DFR (Dihydroflavonol 4-reductase) – A key enzyme in the anthocyanin biosynthesis pathway.

FNS II (Flavone Synthase II) – An enzyme that converts precursors into pale yellow flavones.

Flavonoids – A large group of plant compounds including pigments and co-pigments involved in coloration and UV protection.

Flavones – Pale yellow to nearly colorless pigments that can dilute or mask stronger coloration.

Gene suppression – Turning a gene off or reducing its activity, preventing the production of proteins such as pigment enzymes.

Mutation – A change in DNA that can affect flower color or stability.

Octoploid – Having eight sets of chromosomes; modern dahlias are typically octoploid, which contributes to their genetic complexity.

Periclinal chimera – A plant composed of genetically distinct tissue layers, often resulting in sectoring or variegation. See Chimera.

Pigment precursors – Molecules that are chemically transformed into pigments through enzymatic reactions.

Post-transcriptional gene silencing – A regulatory process where messenger RNA (mRNA) is degraded before it can be used to produce pigment-related proteins.

RNA sequencing (RNA-seq) – A laboratory technique used to determine which genes are active in a given tissue sample.

Seedling – A genetically unique plant grown from seed, often used in breeding to explore new traits.

Somatic mutation – A spontaneous DNA change in an individual plant cell, which may affect flower color in part or whole.

Transposon – A “jumping gene” that can move within the genome, sometimes activating or silencing pigment pathways.

Tuber – A thickened underground root that stores nutrients and allows a dahlia to regrow each season.

Dahlia ‘Tsuki Yori No Shisha’ grown in Washington State (USA). Photo courtesy of Denise Lakin via Facebook. Used by permission. (Author’s image file A-2)

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This article was created through a collaborative process between the author—a dahlia grower and educator—and an AI language model trained on scientific and botanical texts. The author guided the structure, tone, and emphasis of the article, and provided the scientific sources that form its foundation.

The AI was used as a research and writing assistant, helping to summarize technical material, suggest phrasing, and—as part of a guided review process—link every substantive scientific statement, conclusion, and principle to one or more published, peer-reviewed source articles. All content was shaped, reviewed, and refined by the author to ensure clarity and usefulness for readers interested in the science of dahlias.