By Nik Crawley, founder of GardenTrack · Updated July 22, 2026
✓ In your garden
Parris Island Cos is the reference romaine — the tall, upright, self-blanching head that most other romaines are measured against. Bred by Clemson's Charleston station and released in 1951, it earned its place as the standard through sheer uniformity: even, dependable heads with thick crunchy ribs and a sweet blanched heart. The honest truth is that it's a 70-year-old open-pollinated line — rock-solid, but with a disease package that's dated next to modern F1 romaines, and a 'heat tolerance' that vendor copy oversells.
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a classic cos / romaine head on white — tall, upright, elongated with crinkled medium-green outer leaves, pale thick ribs and a blanched heart, the form Parris Island set the standard for · Photo: Fructibus
(CC0, via Wikimedia Commons)
· source
Romaine (Cos)The reference standardCrisp & sweet
“The 1951 benchmark romaine — tall, uniform, self-blanching heads that set the commercial and home standard, with a disease package that's quietly dated next to modern hybrids.”
Days to maturity65–75 days~28–30 for baby-leaf cutting
TypeRomaine / Costall upright self-blanching head
Head8–12 in tallthick crunchy white ribs, pale heart
Best seasonspring & fallcool-season; bolts in heat
ReliabilityThe standard 5/5
Notably uniform head-to-head — its commercial-grade evenness is a big part of why a 1951 open-pollinated line is still one of the most widely grown romaines 70-plus years later.
Crunch & flavorClassic Caesar 5/5
Mild, sweet, and crisp when grown cool, with thick crunchy white ribs and a tender blanched heart — the taste and texture most people picture as romaine.
Disease packageDated 2/5
As a 1951 open-pollinated line it's effectively resistant only to lettuce mosaic virus (and even that's intermediate). It lacks the corky-root, dieback, and multi-race downy-mildew resistances that modern F1 romaines carry.
Heat & bed timeSlow & seasonal 2/5
'Heat-tolerant' is oversold — it still bolts and turns bitter above ~75–80°F. And 65–75 days for a single full head is a long bed occupancy; many growers cut it young as baby leaf instead.
A rock-solid, uniform romaine — just don't expect modern hybrid disease resistance from a 1951 heirloom.
SweetCrispMildNutty ribs
✓ Uniform, crunchy, the romaine benchmark~ Its resistance is dated — space for airflow✗ Not a summer or fast-turnaround lettuce
Numbers from university growing guides. Ratings are our take, judged against all lettuces. Tap a meter to see why.
Growing basics — shared by every head lettuce
Parris Island Cos Lettuce grows like any other head lettuce. The full picture — how deep to plant, spacing, feeding, pests, harvest — lives on the Head Lettuce page so it's maintained in one place.
When to plant Parris Island Cos Lettuce in your zone
Zone 6b
Start seeds indoors
Toughen up outside
Move plants outside
Plant seeds outside
Growing
Picking
Right now · zone 6b · —
—
—
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
early Mar – mid Mar
Toughen up outside
early Apr – mid Apr
Move plants outside
mid Apr – mid Apr
Plant seeds outside
mid Mar – early Apr
Growing
mid Apr – 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 Parris Island Cos Lettuce — and what to keep away
✓ Good neighbors
CarrotsPractical
Quick lettuce fills the row while slow carrots take their time.
TomatoPractical
A tall tomato throws exactly the shade lettuce wants once summer heat makes it flower and turn bitter (bolt).
Onions & garlicTraditional
On the classic charts — lettuce's own row lists onions.
✗ 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 head lettuce.
Pairings compiled from West Virginia University Extension.
Growing Parris Island Cos Lettuce — the things that trip people up
Grow it in the cool of spring and fall. Surface-sow or barely cover the seed (lettuce needs light to germinate), keep the moisture steady, and thin to 10–12 inches for full heads. Consistent water is the single biggest lever for a sweet, crisp heart — and against tipburn.
Don't lean on the 'heat-tolerant' label. It was bred for South Carolina spring and fall, not deep summer — it still bolts and turns bitter above ~75–80°F. Give it afternoon shade in warm zones and harvest before a heat wave.
Its disease resistance is dated (mosaic only), so give plants room for airflow and water at the base. Set your zone on the [lettuce page](/plants/lettuce-head/) to pin your sow and harvest dates. Being open-pollinated, it's easy to save seed from, too.
From university growing guides (see Sources).
Where Parris Island comes from
Parris Island Cos was bred by the Clemson College Truck Experiment Station in Charleston, South Carolina — a USDA-associated program — and released in 1951, introduced commercially by the Ferry-Morse Seed Co. It's a stabilized open-pollinated cross selected for the hot, humid coastal South and for resistance to lettuce mosaic virus. It takes its name from Parris Island, SC.
NC State's cultivar database records it plainly: parentage 'PI 120965 × Dark Green,' characteristics 'tall, dark green,' resistance 'mosaic,' 1951. More than seventy years later it's still one of the most widely grown open-pollinated romaines — the reference point the newer hybrids were built to beat.
Why it became the standard
Parris Island's real superpower is uniformity. It throws tall, upright, cylindrical heads — roughly 8 to 12 inches — that come in remarkably even from plant to plant, with medium-to-dark green savoyed outer leaves cupping a pale, tightly folded heart and thick, crunchy white midribs.
That evenness is exactly what a market grower wants and what makes it dependable in a home bed. It's also self-blanching: the upright leaves shade the heart, so the center turns pale, sweet, and tender on its own. Grown cool, it's mild, sweet, and crisp — the textbook Caesar romaine.
two romaine heads split lengthwise, showing the pale self-blanched hearts and thick crunchy ribs of the cos type · Photo: USDA Agricultural Research Service
(Public domain, via Wikimedia Commons)
· source
The honest catch: its resistance is dated
This is the thing seed copy won't tell you: as a 1951 open-pollinated line, Parris Island is effectively resistant to just one thing — lettuce mosaic virus — and even that is intermediate, not immunity. Cornell lists mosaic as its sole listed resistance. It's susceptible to downy mildew and lacks the corky-root, lettuce-dieback, and multi-race resistances that modern F1 romaines carry.
Watch for marketing that quietly borrows its descendants' résumé. Newer patented romaines were built on the Parris Island plant type and added corky-root and dieback resistance — but the classic heirloom does not have those. None of this makes it a bad choice; it just means you manage it with spacing and airflow rather than relying on genetics. Its tipburn 'tolerance' is only intermediate too — and you often don't see tipburn until you cut the head open.
Growing Parris Island
It's a cool-season crop that grows best around 55–65°F. Direct-sow or transplant in early spring as soon as the soil can be worked, and again in late summer for a fall crop. Surface-sow or barely cover the seed — lettuce needs light to germinate — and thin to about 10–12 inches for full heads, closer for baby leaf.
Consistent moisture is the single biggest lever, both for a sweet, crisp heart and against tipburn. Full sun in cool weather; part or afternoon shade stretches the season as it warms. Harvest the whole head at 8–12 inches (65–75 days), or take outer leaves cut-and-come-again from around 30 days if you'd rather not tie up the bed for the full run.
What goes wrong — and the fixes
Bolting and bitterness in heat. Fix: sow for spring and fall, give afternoon shade and steady water, and harvest before daytime highs settle above ~80°F.
Downy mildew — yellow angular patches with white fuzz on the leaf underside in cool, wet spells — is its real vulnerability, since it lacks modern resistance. Fix: space plants for airflow, avoid overhead evening watering, and rotate away from where lettuce grew last.
Tipburn — brown, dried inner-leaf margins — hides inside the head until you cut it. Fix: keep the soil evenly moist and don't force fast growth with heavy nitrogen. Aphids also hide in the folded heart: check the leaf axils and knock them down before the head closes over them.
In the kitchen
Parris Island is the crisp romaine you already know how to use. Its thick, crunchy ribs and sturdy leaves make it the classic Caesar lettuce, and they hold their crunch in a chopped or composed salad better than a soft leaf would.
The sturdy ribs also mean it takes heat: halved lengthwise and grilled or charred cut-side down, it wilts just enough to soften while the ribs stay structural. And it's a reliable, crunchy sandwich and wrap leaf. Grown cool, the flavor is mild and sweet — bitterness only shows up when heat or bolting stress it.
Parris Island Cos Lettuce head lettuce at a glance
Parris Island Cos Lettuce Head Lettuce — at a glance
Type
Romaine
Days to ripe
56 days after you plant it outside
Color
Green
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 Parris Island Cos Lettuce
How to Plant, Grow, and Harvest Your Own Romaine Lettuce · GardenaryGrow Parris Island Romaine Lettuce in AeroGarden · Enriching Hobbies
Embedded from their creators on YouTube — full credit and views go to the channel.
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Common questions about Parris Island Cos Lettuce
Is Parris Island Cos actually heat-tolerant?
Only relatively. It was bred for South Carolina spring and fall, not deep summer — sustained days above about 75–80°F still bolt it, and bolting turns the leaves bitter. Vendor copy tends to oversell the heat angle; treat it as a cool-season crop and give it afternoon shade in warm zones.
What disease resistance does Parris Island have?
As a 1951 open-pollinated line, effectively just lettuce mosaic virus — and even that is intermediate, not immunity. It's susceptible to downy mildew and lacks the corky-root, dieback, and multi-race resistances that modern F1 romaines carry, so manage it with spacing and airflow.
How big does Parris Island get and when do I harvest?
It forms tall, upright heads about 8–12 inches in roughly 65–75 days. Harvest the whole head once it's full and firm, or take outer leaves cut-and-come-again from around 30 days if you don't want to tie up the bed for the full run.
Can I save seed from Parris Island Cos?
Yes — it's open-pollinated and self-pollinating, so it's easy to save true-to-type. Isolate it modestly from other lettuces flowering at the same time to keep the strain clean. Note that seed from different houses has drifted over the decades, so heads can vary in size strain to strain.
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