By Nik Crawley, founder of GardenTrack · Updated July 22, 2026
✓ In your garden
Dark Opal is the original deep-purple sweet basil — bred at the University of Connecticut in the 1950s and a 1962 All-America Selections winner, one of the very few herbs ever to earn that award. Its violet leaves are milder and earthier than green basil, with a spicy clove-anise note; the signature use is tinting and flavoring herb vinegars. Grow it for the color and drama as much as the taste.
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a full Dark Opal basil plant in a garden bed — deep violet-purple leaves on square stems with pink-lavender flower spikes · Photo: Krzysztof Ziarnek, Kenraiz
(CC BY-SA 4.0, via Wikimedia Commons)
· source
Purple basilHeirloomAnnual
“The 1962 award-winner that made purple basil a garden staple — deep violet leaves, milder and earthier than green basil.”
First snip70–85 daysbaby leaf much sooner
Plant14–20 in bushy~10–12 in wide
Leafdeep violet-purplesometimes green-splashed
Flavormild, earthy, aniseless sweet than green basil
LooksA showpiece 5/5
Deep violet-purple leaves and pink-lavender flower spikes — a dramatic contrast in the bed, on the plate, and steeped into a bottle of vinegar.
FlavorMild & earthy 3/5
Milder and earthier than green sweet basil, less sweet, with a spicy clove-anise note. Pleasant, not a flavor powerhouse — it earns its place on color.
Color stabilityNot perfect 3/5
Being open-pollinated it isn't fully color-stable and can throw green or green-splashed plants; the improved Red Rubin and Purple Ruffles were bred from it for more uniform color.
Flavor strengthTurns sharp if it blooms 3/5
Mild while young; the flavor turns strong and sharp once the plant is allowed to flower, so keep it pinched.
You grow it for the color and the flair — the flavor is the bonus, not the headline.
MildEarthyClove-aniseLess sweet
✓ Color for the bed, plate & vinegar~ Can throw green plants✗ Not the strongest-flavored basil
Numbers from university growing guides. Ratings are our take, judged against all basils. Tap a meter to see why.
Growing basics — shared by every basil
Dark Opal grows like any other basil. The full picture — how deep to plant, spacing, feeding, pests, harvest — lives on the Basil page so it's maintained in one place.
Greenhouse or cover on: your start slides ~4 weeks earlier and your harvest stretches ~3 weeks later (shown striped).
Planting seeds straight in the ground only works where the season's long and warm — most gardeners start seeds indoors or buy young plants, or you'd pick your first tomato right as frost hits.
Comfortable — first ripe fruit lands around late Jun, well before your typical frost (~late Oct).
Start seeds indoors
mid Feb – mid Mar
Toughen up outside
late Apr – early May
Move plants outside
early May – early May
Plant seeds outside
mid Apr – early May
Growing
early May – late Jun
Picking
late Jun until frost (~late Oct)
Typical dates for zone 6b — set your zone or ZIP above for yours.
What to plant near Dark Opal — and what to keep away
✓ Good neighbors
TomatoTrialed
Basil can cut thrips numbers on tomatoes, and a modest yield gain shows up when it is planted at good density. They also want the same heat and water, so the bed suits both.
PepperTraditional
Same bed conditions, same kitchen destiny.
✗ Keep apart
The badge is the honesty.Trialed = a published field trial · Practical = a real mechanism · Traditional = companion-chart lore. These pairings hold for every basil.
Pairings compiled from University of Minnesota Extension, West Virginia University Extension.
Growing Dark Opal — the things that trip people up
Grow it for the color first: deep violet leaves that dress up a bed, a salad, and — its signature move — a bottle of herb vinegar, which it tints and flavors at once.
Pinch regularly and remove flower spikes as they form. It stays mild and bushy while pinched; let it bloom and the flavor turns sharp and strong.
Because it's open-pollinated it isn't perfectly color-stable and can throw the odd green or green-splashed plant — that's normal for Dark Opal, not a seed problem. Rogue out the greenest ones if you want a uniform purple bed.
From university growing guides (see Sources).
Where Dark Opal comes from
Dark Opal was bred at the University of Connecticut in the 1950s by John Scarchuk and Joseph Lent, who selected it from purple-leaved basil to fix a uniform, deep-purple color. Ferry-Morse released it commercially, and in 1962 it became an All-America Selections winner — one of the very few culinary herbs ever to win that award.
In other words, it's the plant that made ornamental purple basil a home-garden staple. The later, more uniform Red Rubin and the frilly Purple Ruffles were both bred as improved selections descended from it.
Dark Opal basil leaves up close — the deep purple-maroon color, with some leaves splashed green (normal for this open-pollinated variety) · Photo: Quinn Dombrowski
(CC BY-SA 2.0, via Wikimedia Commons)
· source
What it tastes like — and what it's for
The honest read: milder and earthier than green sweet basil and noticeably less sweet, with a spicy clove-anise note and crisp-textured leaves. It's pleasant, not a flavor bomb — you grow it mainly for the color.
And the color does real work. Its signature use is steeping herb vinegar, which it tints a jewel pink-purple and flavors at the same time; it also makes a dramatic garnish, a striking addition to a green salad or a tomato plate, and a purple-hued pesto. It carries unusually high anthocyanins, which is why it's even been studied as a natural food dye.
Growing Dark Opal
Grow it like any basil: a tender warm-season annual that dies at frost, wanting full sun, warm soil, and steady water. It makes a compact, bushy plant about 14–20 inches tall — tidy enough to earn a spot in an ornamental border, not just the veg patch.
Full sun deepens the purple; in too much shade the color washes out toward green. Pinch to keep it bushy. Set your zone on the basil page and the calendar pins your sow and plant-out dates.
Why some plants come out green
Here's the quirk to expect: Dark Opal is open-pollinated, so it isn't perfectly color-stable. A sowing can throw the occasional green or green-splashed plant among the deep-purple ones. That's the variety being itself, not bad seed.
If you want a uniformly purple bed, just pull (or eat first) the greenest seedlings and let the darkest ones carry on. Or grow one of its more color-stable descendants — Red Rubin — if uniform purple matters more to you than the heirloom pedigree.
Harvesting so it keeps producing
Pinch and harvest regularly, taking no more than about half the plant at a time so it keeps growing. Follow each flower spike down and cut just above the first leaf pair as buds form.
Timing matters for flavor here: harvesting before or at flowering keeps the leaf mild and the plant bushy, while letting it bloom turns the flavor sharp and strong. Cut in the morning, and harvest heavily before the first frost since one cold night ends it.
What goes wrong — and the fixes
Washed-out color. In too much shade the purple fades toward green; give it full sun to keep the leaves deep violet. And expect the odd green plant regardless — that's the open-pollinated variety, not a mistake.
Bolting and mildew. Heat sends it to flower, which sharpens the leaf, so pinch the buds and keep cutting. Basil downy mildew can hit purple basils too, so keep airflow up, water in the morning, and keep the foliage dry. Being frost-tender, it ends with the first cold night — harvest heavily before then.
Dark Opal basil at a glance
Dark Opal Basil — at a glance
Type
Purple
Days to ripe
70 days after you plant it outside
Color
Purple
Extra fields from seed-catalog listings and university growing guides. Days to ripe and disease resistance shift with your climate and seed source — double-check with your local extension office before you buy.
Watch: growing Dark Opal
How to Grow Basil (complete guide to harvest) · Gardener ScottHow to pick basil for endless harvests · 2 Minute Garden Tips
Embedded from their creators on YouTube — full credit and views go to the channel.
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Common questions about Dark Opal
Is Dark Opal basil edible or just ornamental?
Both — it's a culinary herb as well as an ornamental. The flavor is milder and earthier than green sweet basil with a clove-anise note; its signature culinary use is tinting and flavoring herb vinegars, plus garnishes, salads, and a purple pesto. You grow it as much for the color as the taste.
Why is some of my Dark Opal basil green instead of purple?
That's normal. Dark Opal is open-pollinated and not perfectly color-stable, so a sowing can throw occasional green or green-splashed plants. Full sun deepens the purple; shade washes it toward green. For a uniformly purple bed, remove the greenest plants or grow the more stable Red Rubin.
What does Dark Opal basil taste like?
Milder and earthier than green sweet basil and less sweet, with a spicy clove-anise (licorice) note and crisp leaves. It's pleasant rather than powerful — grown mainly for its dramatic color. The flavor turns sharp if the plant is allowed to flower, so keep it pinched.
How do you use purple basil vinegar?
Pack a jar with Dark Opal leaves, cover with warm white wine or cider vinegar, and steep — the leaves tint the vinegar a jewel pink-purple and flavor it at the same time. Strain and use it in dressings and marinades. It's the variety's signature use.
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