Growing romaine lettuce: A guide from seed to harvest

While there are many different types of lettuce to grow in the garden or in a patio pot, romaine is among my favorites. Yes, I love a good buttercrunch lettuce, but nothing beats the thick, crisp leaves of a head of romaine. Their texture holds a creamy salad dressing like no other leafy green out there. Have you ever tried to put Caesar dressing on bibb lettuce? The results are limp and soggy. Thankfully, growing romaine lettuce is easy, and I recommend every gardener grow a few heads each season.

What is romaine lettuce?

Also known as cos lettuce, botanically speaking, romaine is Lactuca sativa var. longifolia. Instead of growing a round, bulbous head or a loose, leafy one, romaine lettuces grow upright heads with sturdy, elongated leaves that have thick midribs and are densely packed. Romaine is among the most popular lettuces for both home cooks and restaurants, but it’s also been the subject of a handful of E. coli breakouts over the last decade. There’s no better way to ensure the safety of your food than to grow your own, but of course that’s not the only reason to plant this wonderful salad green.

Why you should be growing romaine lettuce

The reasons for growing romaine lettuce go far beyond food safety and its ability to hold a good blue cheese dressing. In my experience, romaine is more resistant to slug and snail damage. They much prefer softer-leaved lettuces in my garden. And, since the heads of romaine lettuce are narrow and upright, you can fit more plants in a given area than you can of the round-headed varieties that spread out wide.

Another benefit of growing romaine lettuce is its ability to stay cleaner. Low-growing, rounded lettuce types are closer to the soil. When it rains, dirt and grit splash up and into the leaves, making them a chore to clean. But, since romaine heads are upright and the crown of the plant is a good 8 to 10 inches above the soil, not as much dirt and grit enter the folds of the lettuce head, making them a snap to rinse off prior to eating.

One final reason to plant romaine lettuce is its heat and cold tolerance. Romaine lettuce is slower to bolt (go to flower) and turn bitter in the heat than many other types of lettuce. And, while all lettuces prefer the cooler temperatures of spring and fall, there are several varieties of romaine lettuce that tolerate surprisingly cold temperatures, affording you the opportunity to extend your harvest into the late fall and even winter if you have a cold frame, cloche, or floating row cover protecting them.

Romaine lettuce varieties

While almost all of the romaine you find in the grocery store consists of the same few green-leaved varieties, there are dozens of types of romaine lettuce you can plant in your garden. Yes, many have green leaves, but there are also romaine lettuces that have wine-colored leaves and others that are bi-color or have deep red speckles on green leaves. Growing romaine lettuce at home enables you to grow some pretty fun varieties that you won’t find in the produce section. Here are some of my favorites.

Red-leaved romaine lettuces
• Pomegranate Crunch
• Intred
• Outredgeous

Bi-colored and speckled romaine lettuces
• Rouge d’hiver
• Truchas
• Flashy Trout’s Back

Green-leaved romaine lettuces
• Rainier
• Paris Island
• Little Gem

For late fall and winter harvests, I recommend ‘Winter Density’. And the one I grow every season, even in the summer, because it’s extremely heat tolerant is ‘Valmaine’.

3 ways of planting romaine lettuce

When it comes to growing romaine lettuce, you have three options for planting.

Option 1: Planting from transplants

The first option is to purchase transplants at your local nursery. This is a great choice for beginner gardeners or those who are not interested in growing from seed. You’ll be able to skip the “nervous parent” stage, but the downside is that you’ll be limited to growing only the romaine varieties the nursery has in stock. Still, if you’re just growing a handful of plants in a pot or the corner of a raised bed, purchasing a starter pack 4 or 6 plants from the nursery is a great way to start.

Option 2: Starting seeds indoors

Another possible way of growing romaine lettuce is to plant seeds indoors under grow lights. Sow the seeds indoors about 10-12 weeks before your last expected spring frost. In my Pennsylvania garden, our last frost occurs around May 15th. If I count backwards 10 to 12 weeks from there, that means I can plant my romaine seeds sometime in late February or early March. Because lettuce is a cool-weather crop that tolerates spring frosts, the plants go out into the garden 4 to 6 weeks after the seeds are sown. That means the seedlings that grow from my late February planting, go out into the garden in early to mid-April. I’ll be harvesting them in May or early June, before the weather warms.

When growing romaine lettuce seeds indoors, have your grow lights on for 14-16 hours per day and keep them just a few inches above the tops of the plants. Keep the seedlings regularly watered and fertilize every two weeks with a seedling-specific fertilizer. Give each seedling plenty of room to grow and pot them up into larger containers as they outgrow the previous one.

One important additional step when growing romaine lettuce seeds indoors is to harden off the seedlings before you plant them out into the garden. This process is a gradual acclimatization to outdoor growing conditions, rather than just throwing them to the wolves, so to speak. Take the seedling trays outdoors in the shade for a few hours a day, gradually increasing the amount of time they spend outdoors and the amount of sun they receive each day. Within about 10 to 14 days, the seedlings are outside full time. Once they are, they’re ready to transplant into the garden.

Option 3: Planting seeds outdoors

Personally, I don’t fuss with planting my romaine lettuce seeds indoors. Instead, I sow the seeds directly into the garden about 6 to 8 weeks before our last spring frost (so here in PA, that means I start sowing lettuce seeds outdoors in late March or early April). Though they are tiny, romaine lettuce seeds are tough. They don’t mind cold soil one bit, they seldom rot in wet ground, and they don’t require any fussing. They are almost foolproof.

Sow romaine lettuce seeds about a half-inch apart. Barely cover the seeds after planting and water them in. Be careful not to wash the seeds away! Then, walk away and forget about them. If you live in a warm climate, such as the Southern U.S., I suggest growing lettuce in the cooler temperatures of winter, rather than in the spring or fall.

When the seedlings are an inch tall, thin them to a distance of 5 or 6 inches apart. If you’d like, you can transplant the culled seedlings to a new spot in the garden, being sure to space them properly. If you don’t thin, your romaine won’t form full-sized heads. Give them room, and they’ll reward you with large, succulent heads.

Growing romaine lettuce in the fall

If you garden in a climate with a hot summer and a cold winter, don’t just grow romaine in the spring. Plant a second crop of romaine by sowing seeds in the late summer for an autumn harvest. The ideal time is 6 to 8 weeks before your first expected fall frost. I sow the romaine seeds directly into the garden in mid to late August, but you may be able to find transplants for fall planting at your local garden center as well. Because the weather can still be quite warm in the late summer here, keep the seeds and plants well-watered.

More tips for growing romaine lettuce

Here are a few additional tips for growing a productive crop of romaine.

1. Amend the soil with finished compost before planting. If you don’t have a home compost bin, purchase bagged compost from a local garden center. Never use fresh manures on or near your lettuce crop – or any other vegetables for that matter (hello, E.coli!).
2. Feed your romaine lettuce with an organic liquid fertilizer every two to three weeks. I use fish hydroslate or a general organic liquid fertilizer such as PlantFuel.
3. To keep slugs from eating your crop, use an organic iron phosphate-based slug bait around the plants.
4. Romaine is harvested as either baby greens or full heads. Baby greens are pinched or cut from the plant when the leaves are as young as 30 days. Leave the growing point intact, and you’ll be able to make multiple harvests of baby greens from the same plant. Or wait until the head reaches full size and then use a sharp knife to cut it off at the base to harvest.
5. Though romaine lettuce is more heat tolerant than other types of lettuce, you’ll want to make your final harvests before hot summer weather arrives. Heat makes the leaves turn bitter.
6. To extend your harvest into hot weather, cover the plants with garden shade cloth to keep them cool.
7. To extend your harvest of fall-grown romaine lettuce, cover the plants with a layer of floating row cover or one of these other garden covers recommended by Niki.
8. If aphids are worrisome on your lettuce crop, interplant with sweet alyssum. As noted in my book about science-based companion planting, Plant Partners, sweet alyssum blooms are very attractive to several different predators of aphids, including parasitic wasps, ladybugs, and hover flies.
9. Romaine lettuce is easy to grow in a pot. Use high-quality potting soil or one of our DIY potting soil recipes found here. Make sure the pot holds 2 gallons of potting soil for every head of lettuce you grow in it. That means that if you want to grow three heads of romaine, choose a pot that holds 6 gallons of potting soil.

Growing romaine lettuce is a fun and easy endeavor. The results are crisp, healthy, delicious, and well worth the effort.

For more tips on growing lettuce and other veggies, please visit the following articles:
• Step by step instructions for growing all types of lettuce
• Tomato growing secrets
• Zucchini companion plants
• How to grow cabbage
• Growing Brussels sprouts