How to Plant, Grow, and Care for Romaine Lettuce

When it comes to popular types of lettuce, romaine makes its way to the top. These elongated heads produce boat-like leaves made up of a crunchy midrib and tender green. Romaine is a key ingredient in Caesar salad, but it also works well for lettuce wraps and holds up to the high heat of a grill.

Growing romaine at home isn’t difficult, but it requires the right environment and the proper care. I’ll share how to start romaine from seed, transplant it into your garden, and care for it until it’s ready to harvest.

Characteristics

Romaine has an upright growth form and features thick and crunchy midribs that taper toward the tops of the leaves. These greens are tougher than other lettuce varieties, but they’re still tender enough to enjoy in salads.

The plants grow as vegetative annuals that thrive in the cool temperatures of spring and fall. Most varieties are deep green, but you can also find red cultivars.

Native Area

Romaine is native to parts of the Mediterranean and western Asia. While historians believe humans bred modern lettuce varieties from prickly wild plants, this is one of the oldest cultivated lettuces. People have been growing it for thousands of years! 

Planting

These greens will grow well in well-draining soil in the ground, raised beds, and containers. The plants prefer cool weather, so spring and fall growing is ideal. However, with the right type of protection, you can extend the season into the summer and winter.

Determining When to Plant Romaine

Since lettuce grows well in cool temperatures, spring and early fall are the best times to plant romaine. Wait until the danger of frost has passed in the spring before planting, and aim to transplant or direct sow at least ten weeks before the first frost in the fall.

Depending on where you live, you may be able to grow it throughout the summer and into the winter. Space your planting dates two weeks apart if you want to enjoy multiple harvests.

Transplanting

Unless you’re growing baby greens, I recommend transplanting over direct sowing. Planting seedlings in the garden ensures the plants are at the proper spacing and ensures the seeds germinate well, even when the soil is hot or cold.

After confirming your growing space is suitable, mark out the correct spacing. Full-size romaine prefers spacing between 10-12 inches, and mini varieties like ‘Little Gem’ grow well closer to six inches apart.

Growing from Seed

If you want to grow romaine from seed, you can start transplants indoors or direct sow the seeds in your garden. Starting indoors gives you a head start on the growing season, while direct sowing removes the hassle and equipment required to grow seedlings.

How to Start Romaine Seeds Indoors

Starting seeds indoors allows for excellent germination and ensures you’ll end up with healthy seedlings. It also allows you to harvest mature heads a few weeks earlier in the spring than if you direct sow the seeds.

Aim to start seeds four to six weeks before transplanting—this will give you seedlings that are a few inches tall when planting time arrives. Although mature plants can tolerate light frosts, tender seedlings are susceptible to cold damage. Therefore, you should sow spring seeds about four weeks before your last spring frost.

Start by making soil blocks or filling cell trays with a well-draining seedling mix. Place one to two seeds per cell and cover with a quarter of an inch of potting soil. Water well and set the seeds in a cool location between 60-70°F (16-21°C).

You should see seedlings emerge within a week. Once the sprouts break through the soil, place them in a location that receives at least eight hours of bright light. A grow light can provide direct light if you don’t have access to a greenhouse or sunny windowsill.

Continue to water the soil so it stays moderately moist. The seedlings should be a few inches tall and ready to transplant within four to six weeks. Before you plant them outdoors, make sure to slowly acclimate them to their new home to decrease transplant shock.

How to Direct Sow

Direct sowing works well if you want to grow baby greens or hope to skip the steps involved in growing transplants. Since lettuce seeds won’t germinate well when the soil is over 80°F (27°C), direct sowing works best in the spring and fall.

If you want to grow baby romaine, space the seeds a few inches apart. Allowing a foot of space between seeds will provide the plants with the room they need to grow into mature heads.

Regardless of your spacing, sow the seeds a quarter of an inch under the ground. Keep the soil moist for a week or until the seeds germinate. If you planted multiple seeds in the same hole, thin the seedlings to a single plant when they’re one to two inches tall.

How to Grow

If you grow romaine in the spring and fall, it’s easy to care for. However, it’s more challenging to maintain healthy plants in the summer and winter.

Light

Although this variety doesn’t grow well at high temperatures, it thrives with lots of sun. The plants need at least six hours of light each day to receive the energy they need to remain healthy and grow into robust heads. They can tolerate partial shade, especially during hot afternoons.

Water

Romaine lettuce prefers well-draining soil that remains slightly moist. Young seedlings have small root systems, so they don’t tolerate dry spells as well as larger plants with deeper and wider roots.

Since wet leaves can encourage the development of diseases, drip irrigation is better than overhead irrigation. You can either set up a drip irrigation system or water the base of your plants with a hose or watering can.

Soil

This green grows best in well-draining soil that allows excess water to escape. Although the plants require moderate amounts of water to remain healthy and develop crisp foliage, standing water can lead to harmful diseases. If your soil is compacted, aerate it before planting.

Temperature and Humidity

Romaine, like most lettuce, grows best in cool temperatures between 50-75°F (10-24°C). That’s why spring and fall are the best times to enjoy a sweet, crisp head in salads and on burgers. 

A few hot days won’t damage the plants, but prolonged temperatures above 80°F (27°C) can cause the plants to bolt. While flowering lettuce is okay to eat, it has a bitter flavor that makes it unpalatable.

Although farmers sometimes implement practices like misting and shade cloth to allow for summer lettuce harvests, this may be overkill for a small garden. If you really want to grow lettuce in the summer, opt for heat-tolerant Batavian varieties over romaine.

Fertilizing

This crop is a light feeder, so you don’t have to apply large doses of fertilizer to keep the plants happy. However, small amounts of nitrogen and other nutrients will result in larger yields and resistance to bolting. 

Conducting a soil test and applying the necessary nutrients is always the best practice. However, you can also add a small amount of nutrient-rich compost or balanced vegetable fertilizer at planting time.

Maintenance

Romaine lettuce doesn’t require much maintenance outside of regular care. Keep the soil moderately moist, remove weeds around the plants, and regularly check the growing plants for pests.

Harvesting and Storage

You can harvest this crop at any time, but most growers wait until the plants form crunchy midribs and dense heads. Large varieties like ‘Vivian’ and ‘Coastal Star’ are ready to harvest in around 50-60 days after transplanting. Miniature varieties will be mature in closer to 40 days.

Harvesting in the morning or evening is best. Use a sharp knife to cut the head near the soil surface, then remove any dirty or discolored leaves. You can enjoy the leaves immediately after harvest or store them in your refrigerator for up to a week.

Common Problems

Romaine is susceptible to numerous diseases, pests, and environmental issues. Knowing the common problems can help you keep your plants happy.

Pests

Although romaine isn’t as susceptible to pests as some other common vegetable crops, it can still experience a fair amount of pest pressure. Most of the insects that attack romaine are generalists that also feed on other crops. That means keeping your entire garden free from critters like aphids, armyworms, and thrips will help keep your lettuce crop healthy.

Aphids

These tiny sap-sucking pests may not appear like a huge threat, but growers who have dealt with aphids know they can quickly ruin an entire garden. Aphids use their piercing mouthparts to drink sap out of lettuce leaves. Although a few of these insects won’t cause severe damage, large infestations can quickly weaken plants and spread diseases.

Since aphids multiply rapidly, treating them as soon as you spot them is key to limiting their spread. Natural predators like ladybugs, green lacewings, and hoverflies can control aphid outbreaks when they’re still small, but intervention is often necessary when you spot dozens or hundreds of problematic insects. Spraying aphids with neem oil or insecticidal soap will provide effective treatment.

Thrips

If you notice your normally green or red romaine leaves have developed an unusual silvery sheen coupled with small brown dots, thrips are likely to blame. These elongated insects remain less than an inch long and appear in colors including white, yellow, and brown. Natural predators like green lacewings and predatory mites often keep thrips in check, but the pests can sometimes get out of control.

If you notice damage on your leaves, carefully check them for thrips. Since the damage only becomes noticeable after the plant grows, thrips are often gone by the time you’ve spotted the damage. Therefore, treating the pests is rarely necessary.

Prevention is often a better way to handle thrips in the garden. Planting a diverse array of crops will support predators that help keep thrips in check, and covering lettuce seedlings with insect netting at planting will physically exclude the pests.

Diseases

Romaine, like most types of lettuce, is susceptible to numerous diseases. Many of these diseases are difficult to treat once they appear, so prevention is often the best strategy.

Botrytis

Also known as gray mold, this common fungal disease is caused by Botrytis cinerea. The symptoms start as wilted and yellowing lower leaves, and eventually, whole heads wilt and turn brown.

Since botrytis is difficult to treat, prevention is the best strategy. Always plant romaine in well-draining soil and irrigate only when necessary. If you spot diseased plants, remove them from your garden as soon as possible.

Anthracnose

While anthracnose often refers to fungal diseases caused by pathogens in the Colletothrichum genus, lettuce anthracnose is caused by a different species. Microdochium panattonianum is host-specific, meaning it only infects lettuce crops.

The main symptoms of anthracnose on romaine are small, dark spots on the leaves. The centers of the spots eventually disappear, giving the disease the nickname shot-hole. Rotating crops, keeping the soil on the drier side, and avoiding splashing water are all ways to prevent the disease.

Leaf Drop

These fungal diseases are caused by pathogens in the Sclerotinia genus. If you pay close attention, you may notice lower leaves and stems turning brown. However, many gardeners only recognize these fungi are present when entire heads of lettuce appear to wilt overnight.

Sclerotinia fungi are more likely to thrive in cool and wet environments, so always plant romaine in well-draining soil and only water when dry. Remove any infected plants as soon as you spot them.