Black Dahlias Aren’t Black: ‘Karma Choc’ Carries Up to 22x the Pigment of a Red Dahlia, and 8 Near-Black Varieties Ranked by the Evidence
Lab tests found 8-33 µmol of pigment per gram in ‘black’ dahlias vs 1-2 in red ones. See why black dahlias fade and which 8 near-black varieties to plant.
No dahlia is truly black. When a 2012 study measured the petals of 14 cultivars sold as “black,” it found 8 to 33 micromoles of red-purple anthocyanin pigment per gram of fresh petal. Two red dahlias tested alongside them carried 1 and 2. ‘Karma Choc’ came in at 22. A black dahlia is a red one with so much pigment packed in that the petal absorbs most of the light that lands on it.
That changes how you pick and place them. The same study found that black dahlias lose depth as each petal ages, so older petals turn dark red, and red dahlias don’t do that. Whether full sun makes the loss worse is less settled: I couldn’t find a single dahlia study that separates sunlight from heat. Below is what the lab data does and doesn’t say, a fading diagnostic table, and eight near-black varieties ranked by the evidence rather than by catalog adjectives.
What makes a dahlia petal look black?
A black dahlia petal is packed with cyanidin-type anthocyanins and has almost no flavones to compete with them. Dahlias make both pigment families from the same starting material. Anthocyanins are the red and purple ones. Flavones are nearly colorless. The Thill team’s paper, whose title is “A decline in flavone formation correlates with the rare color of black dahlia flowers,” found that black cultivars switch flavone production down, so more of the shared raw material ends up as red-purple pigment.
The type of anthocyanin matters too. Dahlias carry two families: pelargonidin (orange-red) and cyanidin (deeper, bluer red). A 2016 Japanese study by Deguchi and colleagues purified the four main dahlia anthocyanins and measured the color of each in solution. Cyanidin-based pigment lowered lightness and color intensity more than the pelargonidin version, and the authors concluded that high cyanidin accumulation is critical for black coloring in dahlias.
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The two papers don’t fully agree, and that’s worth knowing. Thill’s team concluded that “black hues depend on the anthocyanin concentration rather than on the anthocyanin pattern,” and one of their black cultivars, ‘Black Barbara’, was only 9% cyanidin. Deguchi’s cultivars pointed the other way. The practical reading is that the darkest dahlias have both: a lot of pigment and a high cyanidin share.
How much pigment does a “black” dahlia carry? The lab numbers
The table below is pulled from Table 1 of the Thill study. It lists the red comparison cultivars, five of the black cultivars gardeners can actually buy, and the two extremes, ‘Black Barbara’ and ‘Tisa’. In short: every black cultivar carried several times the pigment of the two reds, but the amount alone doesn’t predict how dark a flower looks.
| Cultivar | Sold as | Anthocyanin (µmol/g) | Cyanidin share | Flavone (µmol/g) |
|---|---|---|---|---|
| ‘Cheerio’ | Red | 1 | 30% | 8 |
| ‘Feuerschein’ | Bright red | 2 | 15% | 68 |
| ‘Chat Noir’ | Black | 8 | 72% | 3 |
| ‘Black Jack’ | Black | 13 | 78% | 8 |
| ‘Aurora’s Kiss’ | Black | 15 | 65% | 9 |
| ‘Arabian Night’ | Black | 19 | 59% | 5 |
| ‘Black Barbara’ | Black | 21 | 9% | 122 |
| ‘Karma Choc’ | Black | 22 | 75% | 2 |
| ‘Tisa’ | Black | 33 | 58% | 1 |
Here’s what I take from those rows. This is my reading of the table, not a formula the authors tested.
Quantity separates black from red. ‘Karma Choc’ carries 11 times the pigment of ‘Feuerschein’ and 22 times that of ‘Cheerio’. That “up to 22x” is real but rests on just two red cultivars, so treat it as an illustration of scale, not a universal ratio.
Quantity isn’t the whole recipe. ‘Chat Noir’ has only 8 µmol/g, the lowest of any cultivar here, yet it counts as black because 72% of its pigment is cyanidin and it carries just 3 µmol/g of flavone. ‘Black Barbara’ has 21 µmol/g, but it’s only 9% cyanidin and carries 122 µmol/g of flavone, the most in the study, so it’s the odd one out.
‘Karma Choc’ and ‘Black Jack’ get there by different routes. ‘Karma Choc’ is the quantity play: 22 µmol/g with almost no flavone. ‘Black Jack’ is the quality play: a modest 13 µmol/g, but a 78% cyanidin share, one of the highest in the study.
Know the limits of this data. Each cultivar was sampled once, from European suppliers. The authors grouped cultivars as “black” without naming a color standard, and they measured pigment in extracts, not color under sunlight. Only a handful of black cultivars exist among more than 20,000 garden dahlias, so this is a small club, but it is a thinly measured one.
Do black dahlias fade in full sun? What the research does and doesn’t say
Black dahlias lose depth in at least three ways, and only the first has been documented in black dahlias themselves.
1. Petal age (documented). Thill’s team reports that “black colouration fades during petal aging and older petals appear dark red rather than black,” and that this isn’t seen in red cultivars. They link it to a sharp drop in the ratio of colorless copigments to anthocyanins in black cultivars and suggest that “might influence the colour stability.” That is a hypothesis, not a proven cause.
2. Heat (strong hint, different species). Longfield Gardens, a bulb retailer, says very hot weather or intense sun can break down the dark pigments, that early blooms may look burgundy after hot nights, and that later flowers darken as nights cool. That’s grower experience, not a trial. The closest controlled evidence is from chrysanthemum: a 2022 Frontiers in Plant Science study held plants at 38°C (about 100°F) by day and 22°C (about 72°F) at night. Anthocyanin in the ray florets of the heat-sensitive ‘Nannong Ziyunying’ fell from 27.89 to 10.19 optical-density units per gram of fresh weight, and the flowers of both cultivars tested faded. Chrysanthemums aren’t dahlias, but they’re in the same daisy family, so the mechanism is plausible. It isn’t proven for dahlias.
3. Cold nights (indirect). A 2024 study in The Horticulture Journal tied color fading in the dark red dahlia ‘Nessho’ to low minimum temperatures. Faded orange flowers held more flavone than dark red ones. ‘Nessho’ isn’t a black cultivar, so this only hints at why late-autumn blooms sometimes turn rusty.
What about sunlight itself? I found no study that tests sunlight apart from heat on a black dahlia. Retailers also point out that dark petals absorb more heat, which would tie sun and heat together, but that’s reasoning, not a measurement. Treat “full sun fades them” as a reasonable grower rule, not an established result.
Fading diagnostic: what you’re seeing and what to do
The most useful single rule: judge a black dahlia in September, not July. Use the table to work out which of the causes above you’re looking at.
| What you see | Likely cause | How solid is the evidence? | What to do |
|---|---|---|---|
| Early blooms look burgundy or red-brown; later ones are darker | Hot nights early in the season | Grower report (Longfield) | Wait for cooler nights; mulch to keep roots cool |
| A single bloom slides from near-black to dark red over its life | Normal petal aging | Documented (Thill 2012) | Cut blooms fresh; deadhead old ones |
| Bleached or scorched petals on the afternoon-sun side | Heat and sun stress | Grower report plus a chrysanthemum study | Give afternoon shade in hot climates; water deeply |
| Rusty or orange tones after the first cold nights | Low-temperature shift toward flavones | Indirect (a dark red cultivar, not a black one) | Cut before frost; this is the season ending |
| Blooms turn purple, foliage is mottled or stunted | Possible virus | Deguchi 2016: tobacco streak virus turned black cultivars purple | Inspect leaves, then check the dahlia diseases guide; remove infected plants |
| Tall, leggy plant, few blooms, flat color | Too little light | Grower report (Longfield) | Move to a spot with 6 to 8 hours of direct sun |
8 near-black dahlias, ranked by the evidence
Five of these eight have measured pigment data, so they come first, ordered by anthocyanin content. The last three have never been measured, so I ranked them by how their growers and the RHS describe the color. Understand what this ranking is: it ranks pigment in reserve, not how dark each variety looks in your border. My working assumption, which is untested, is that more pigment means more depth to lose before a bloom slides toward red. Nobody has published a side-by-side sun test of these varieties.
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→ View My Garden Calendar| Rank | Variety | Form | Height | Evidence for darkness |
|---|---|---|---|---|
| 1 | ‘Karma Choc’ | Decorative | 2 to 3 ft | 22 µmol/g, flavone 2 |
| 2 | ‘Arabian Night’ | Formal decorative | About 3 ft | 19 µmol/g, flavone 5 |
| 3 | ‘Aurora’s Kiss’ | Miniature ball | About 4 ft | 15 µmol/g, flavone 9 |
| 4 | ‘Black Jack’ | Semi-cactus | 3 to 5 ft | 13 µmol/g, 78% cyanidin |
| 5 | ‘Chat Noir’ | Semi-cactus | About 5.5 ft | 8 µmol/g, 72% cyanidin |
| 6 | ‘Verrone’s Obsidian’ | Orchid | Medium | Not measured; “deepest black” per Floret |
| 7 | ‘Nuit d’Été’ | Semi-cactus | About 4 ft | Not measured; centers “almost black” per RHS |
| 8 | ‘Rip City’ | Informal decorative | Low-growing | Not measured; “chocolaty-red” per Floret |
Heights come from the RHS and the growers cited in Sources, converted to feet. The RHS gives ‘Karma Choc’ as 1.6 to 3.3 ft and ‘Black Jack’ as 3.3 to 5 ft, so treat every height as a range.
1. ‘Karma Choc’
The pigment leader among varieties you can easily buy. The RHS describes “a decorative dahlia with velvety very dark red flowers,” and it holds the Award of Garden Merit. Its flavone reading of 2 µmol/g is among the lowest in the study, which fits the black-dahlia recipe. It’s a good first pick if you want one dahlia to test the idea on.
2. ‘Arabian Night’
The RHS calls the flowers “dark red flowers verging on black,” about 4 inches across, and Longfield says the center “looks almost like ink.” Its cyanidin share (59%) is the lowest of the top five, so it leans on sheer quantity. Note the RHS says “verging on,” not “black.” Even the catalog authorities hedge.
3. ‘Aurora’s Kiss’
A miniature ball with small, dark red flowers on a plant about 4 ft tall but only about 16 inches wide, according to Gardeners’ World. That narrow footprint suits tight borders. It’s tender, so lift the tubers after the first frosts, and deadhead regularly.
4. ‘Black Jack’
The RHS describes large semi-cactus flowers that are “very dark red, almost black, with long, pointed petals, rolled under at the edges, giving a spiky effect,” from midsummer until the first frost. Its 13 µmol/g is modest, but the 78% cyanidin share suggests its darkness depends on pigment quality, not volume. Expect a plant up to about 4.5 ft.
5. ‘Chat Noir’
This is the honest surprise on the list. It has the lowest pigment content in the lab data (8 µmol/g), and the RHS calls the flowers “rich, red-purple… tinged with grey towards the centre,” not black. Longfield says it leans toward black in the center. It earns its slot with a tall, award-winning plant (AGM, about 5.5 ft) and 6-inch flowers, but buy it for the dark crimson, not for jet black.
6. ‘Verrone’s Obsidian’
Floret calls its star-shaped blooms “the deepest black” and lists an orchid form with 4 to 5 inch flowers. The single ring of near-black petals around a bright yellow center is a very different look from the double dahlias above. One catch: sellers disagree on the form class (orchid, collarette, even single), so check what a given supplier ships.
7. ‘Nuit d’Été’
The RHS describes 8-inch semi-cactus heads “of deep crimson florets, the central florets almost black.” Here the black is a center effect, not an overall one, which matters for how it reads from a distance. It grows to about 4 ft.
8. ‘Rip City’
Floret lists “rich chocolaty-red, slightly nodding blooms” of 4 to 6 inches on a low-growing plant, and Longfield describes a very dark center with deeper garnet outer petals. It’s the least black on the list, and I include it for gardeners who’d rather have chocolate than ink.
Three cultivars with strong pigment readings didn’t make the list: ‘Tisa’ (33 µmol/g, the highest in the study), ‘Black Barbara’ (21) and ‘Magic Night’ (18). I couldn’t confirm their form or find them reliably sold. If a supplier near you stocks ‘Tisa’, it’s worth a trial. Compare the full range of shapes in our dahlia form classes guide, because pigment and flower form are independent choices.
How to keep near-black dahlias dark: site and season
Give them 6 to 8 hours of direct sun, but match the afternoon exposure to your summers. Longfield recommends full sun for strong stems and steady flowering, with morning sun and dappled afternoon shade in hot regions, plus mulch in the South. That fits the heat evidence above.
| Your climate | Sun plan | Extra step |
|---|---|---|
| Hot summers (US South, Southwest, inland California) | Morning sun, dappled shade through the hottest part of the afternoon | Mulch; judge color in September and October |
| Mild or cool summers (UK, Pacific Northwest, northern states) | Full sun all day | Cooler weather slows pigment breakdown, so full sun should cost you less color (my inference from the retailer’s reasoning) |
Three habits help in any climate. First, cut flowers while they’re fresh, since each petal loses depth with age (the cutting guide covers harvest stage). Second, pinch and feed as you would any dahlia; the RHS advises full sun, fertile well-drained soil, pinching the growing tips and generous watering in dry spells. Third, lift and store the tubers after frost has blackened the foliage, as the RHS advises. Our dahlia growing guide has the planting dates and the storage routine.
One idea I haven’t seen tested: because blooms look darkest in late summer and autumn, a slightly later planting date that pushes your main flush past the hottest weeks may pay off. Treat that as an experiment, not advice backed by data.
Plant near-black dahlias with something pale
Never plant black dahlias alone. A solid mass of near-black petals reads as a hole in the border, especially from a distance or in shade, and the depth you paid for disappears. That’s a design judgment, not research, but it’s the one I’d stake the most on.
Pair them with silver and white. Silver-leaved artemisia gives a pale, fine-textured backdrop, and white cosmos blooms through the same season in full sun, so the contrast shows when the dahlias are at their best. Our dahlia color combinations guide covers 20 more pairings, including ‘Karma Choc’ and ‘Arabian Night’ with yellow and chartreuse partners, and the dahlia companion plants guide covers pest-side pairings.
Frequently asked questions
Is there a truly black dahlia?
No. Longfield Gardens notes that no dahlia species grows wild with black flowers, and the 2012 lab study found “black” cultivars carrying 8 to 33 µmol/g of red-purple anthocyanin, against 1 to 2 for red ones. The black is concentrated red and purple pigment.
Which black dahlia is the darkest?
Among cultivars gardeners can easily buy, ‘Karma Choc’ had the highest measured pigment (22 µmol/g) in the lab study, with ‘Arabian Night’ next (19). ‘Tisa’ was higher (33) but is hard to find. “Darkest” depends on cyanidin share and flavone too, so a pigment number alone won’t settle it.
Why is my black dahlia red or burgundy?
Most often it’s petal age, heat or hot nights. Older petals turn dark red (documented), and growers report burgundy blooms after hot nights that darken as nights cool. If the color turns purple and the leaves look mottled, check for virus.
Do black dahlias fade in full sun?
Growers report that intense afternoon sun and heat fade them; a chrysanthemum study shows heat cutting petal anthocyanin sharply. No study separates sun from heat on a black dahlia, so afternoon shade is a sensible precaution in hot climates.
Are black dahlias harder to grow than other dahlias?
No. The RHS gives the same cultivation advice for the genus: full sun, fertile well-drained soil, pinching, generous watering in dry spells, and lifting tubers after frost. The extra work is managing color, not the plant.
Sources
- Thill J, Miosic S, Ahmed R, et al. ‘Le Rouge et le Noir’: A decline in flavone formation correlates with the rare color of black dahlia (Dahlia variabilis hort.) flowers. BMC Plant Biology 12:225 (2012)
- Deguchi A, Tatsuzawa F, Hosokawa M, Doi M, Ohno S. Quantitative Evaluation of the Contribution of Four Major Anthocyanins to Black Flower Coloring of Dahlia Petals. The Horticulture Journal 85(4):340-350 (2016)
- Muthamia EK, et al. Elucidation of Low-temperature Regulated Flavone Synthesis in Dahlia Variabilis and its Effects on Flower Color. The Horticulture Journal 93(4):335-343 (2024)
- Shi Z, Han X, Wang G, et al. Transcriptome analysis reveals chrysanthemum flower discoloration under high-temperature stress. Frontiers in Plant Science 13:1003635 (2022)
- Royal Horticultural Society. Dahlia ‘Karma Choc’ PBR (D). RHS Plants
- Royal Horticultural Society. Dahlia ‘Black Jack’ (S-c). RHS Plants
- Royal Horticultural Society. Dahlia ‘Chat Noir’ (S-c). RHS Plants
- Royal Horticultural Society. Dahlia ‘Arabian Night’ (D). RHS Plants
- Royal Horticultural Society. Dahlia ‘Nuit d’Été’ (C). RHS Plants
- BBC Gardeners’ World. Dahlia ‘Aurora’s Kiss’. Gardeners’ World Plant Finder
- Floret Flower Farm. Dahlia ‘Verrone’s Obsidian’. Floret Library
- Floret Flower Farm. Dahlia ‘Rip City’. Floret Library
- Longfield Gardens. Is Black Dahlia a Real Plant? The Truth About Dark Blooms. Longfield Gardens
- Longfield Gardens. Where Do Black Dahlias Grow for the Best Blooms? Longfield Gardens
