Lettuces are versatile plants, and the widespread cultivation of lettuce means we have plenty of varieties to choose from. Some lettuce varieties will happily grow in part shade, and others in full sun, and many varieties are well suited to small-space gardening. In fact, choosing a lettuce variety, a good pot, and the right soil and the three first steps to growing healthy, abundant lettuce in containers.
This guide covers how to grow lettuce from seed, whether you're transplanting it into containers or direct sowing. Read on for all the information you'll need, from choosing a pot, soil, and variety to plant care and harvesting tips.
Skip Ahead: Pots • Lettuce varieties for containers • Soil • When to plant • Starting seeds indoors • Transplanting lettuce • Direct sowing • Spacing • Growing • Harvesting
Selecting pots for lettuce
There are a few factors to consider when choosing a container: width, depth, material, and drainage holes.
Loose-leaf lettuce plants want containers that are at least 6 inches deep, and ideally 8-10 inches deep. Head lettuce, like romaine varieties, do best in pots that are anywhere from 8-12 inches deep. No matter the container's size, it should have drainage holes.
Depth and Width
Planting lettuce into shallow containers can stunt growth in a few ways. To start, the soil will dry out more quickly, causing the plant to send its energy into the roots instead of the leaves. This results in plants with excessive root systems and relatively little foliage. The plants may also suffer from a lack of nutrition and may need to be top-dressed with compost or fertilized more frequently.
If you're planting lettuce into shallow pots, you can help the plants by choosing containers that are wider. This will give extra space for the roots to grow and for more compost. Windowsill containers are a great example of this.
Material
Lettuces like moist soil, and soil in containers tends to dry out quickly, so it's best to choose a pot that won't absorb any water. Plastic or glazed ceramic are ideal.
Terracotta or clay pots are porous, making them great for Mediterranean herbs but poorly suited to lettuce and other thirsty plants. Metal containers can work well, but they'll also heat up the soil when placed in full sun. Wooden containers are often treated to be water-resistant, but those chemicals will leach into the soil. Untreated cedar planter boxes are the best option for long-lasting wood containers, but be mindful that they will absorb some of the soil's water.
Drainage holes
Whichever material, size, or shape you go with, your container must have drainage holes. Pots without drainage holes accumulate water and inevitably cause the roots to rot. If your container doesn't have holes-- say, if you're using a repurposed bucket or galvanized tub-- drill some into it.
If your pots are going to sit on the ground, you can also purchase terracotta 'feet' to prop them up. This will aid the pot in allowing all excess water to drain out.
Lettuce varieties for containers
Some types of lettuce have been bred specifically to be container-friendly, and others are naturally more compact or have a smaller growth habit. Luckily, lettuce has been in wide cultivation for so long that there are now container-friendly varieties of every type:
- Loose leaf: Salad Bowl lettuce is a popular heirloom loose leaf variety, thanks to its heat and frost tolerance. It grows rich, red and green leaves that reach up to 8 inches tall. New Red Fire lettuce is a great disease-resistant variety that produces tall green leaves with red tips. It's frost tolerant and it's also relatively slow to bolt in the heat. Brentwood is a compact variety with burgundy leaves that grow to just 4 inches tall. It's also resistant to downy mildew and fusarium wilt.
- Romaine (cos): Truchas Mini-Romaine is a deep red romaine variety with upright leaves that grow to 6-8 inches tall. It's a frost-tolerant and bred for its compact size and disease resistance.
- Butterhead: Buttercrunch is a frost-tolerant variety that grows to 3-5 inches tall and needs just 6 inches of spacing. It grows a loose head of creamy, light green leaves and can tolerate part shade.
- Iceberg: Great Lakes 118 is a classic, light green crisphead variety that grows well in containers, reaching 6 inches in diameter. It's a great summer lettuce variety, thanks to its heat resistance. Ice Queen is a popular crisphead variety with less compact outer leaves that can be harvested as soon as 20 days after sowing, while you wait for the plant to mature. It will tolerate full sun or partial shade, and is both heat and frost tolerant.
Read More: 8 Easy-to-Grow Summer Lettuce Varieties
Choosing soil
Lettuce prefers sandy soil with plenty of nutrition. You can create the perfect lettuce soil mix at home by combining a good potting mix with compost and adding vermiculite or sand for drainage.
When to sow lettuce seeds
Lettuces are cool weather vegetables, preferring to grow in the spring, fall, and even winter in mild climates. Most lettuce varieties will quickly go to seed once temperatures start to climb in the summer, although there are a few summer lettuce varieties that do very well given the right conditions.
As a general guideline, here's when to sow lettuce seeds, depending on when you want to harvest them:
- Spring harvest: Sow seeds indoors 4-6 weeks before your last frost date
- Summer harvest: Sow seeds indoors 4-6 weeks before your last frost date, or sow directly once soil temperature has warmed (about 2-4 weeks before the last frost)
- Fall harvest: Sow seeds indoors 4-6 weeks before your first frost date
- Winter harvest: Sow seeds directly once temperatures have dropped in late summer. In mild climates, seeds can be sown directly well into the winter months.
After your first lettuce sowing in the spring, you can also succession sow seeds every 2-4 weeks to provide a continuous harvest throughout the season.
Starting lettuce seeds indoors
Sowing seeds inside gives the gardener a jump on the season in the very early spring and fall, but it's also useful in the summer months. When soil temperatures are too warm (above 80ºF), lettuce seeds will struggle to germinate. In the late summer, sowing lettuce indoors allows us to get a headstart on growing fall lettuces.
For gardeners who struggle with protecting tender seedlings from rodents, slugs, armyworms, cutworms, and other garden 'pests,' starting lettuce indoors also allows the lettuces to become sturdy, resilient plants before going outside.
Skip ahead if you want to direct sow lettuce seedlings.
To start, you'll need seedling trays, a seed starting mix, and your lettuce seeds.
- Fill seedling plugs with a well-draining seed starting mix. Water the mix thoroughly before adding the seeds. Sow two or three lettuce seeds into each plug, placing them onto the surface of the soil and gently pressing them down. A light covering with soil or vermiculite will help keep the seeds in place.
- Water in the seeds generously. Bottom watering helps ensure the seeds aren't dislodged, but isn't crucial.
- Place the trays or pots in a sunny place. This way, when seedlings emerge, they'll have immediate access to sunlight.
- Water the seeds lightly when the soil dries out. This ensures that when seeds do start to sprout, they'll have access to water. Take care not to waterlog the soil.
- Lettuce seedlings should emerge within 5-14 days as long as they're kept somewhere with daytime temperatures around 60-70ºF.
- Thin to one seedling per plug once they've developed their cotyledons (first sets of leaves, or 'seed' leaves).
- Transplant the seedlings into larger pots or cells once they have developed their first sets of true leaves. At this point, plant them into a potting mix that will provide nutrients to help the plants grow further.
- Harden off the seedlings gradually once they are a few inches tall. Over the course of one to two weeks, take the seedlings outside for increasing durations until they can stay outside overnight. A good way to start is by placing them in a shady spot for a few hours.
Transplanting lettuce into pots
Once your lettuce seedlings are hardened off and have developed healthy root systems in their starter pots, it's time to plant them into their final containers. Here's how to do that, step by step:
- Prepare your soil by combining a potting mix with compost and a generous amount of drainage-- either vermiculite or sand. Fill your container to 3-4 inches below the rim.
- Prepare holes using a dibber, spade, or your hands.
- Lift lettuce seedlings out of their containers, being careful not to damage the roots. Some lettuce varieties have more fragile root systems than others, so it's best to be gentle at this stage.
- Place the seedlings in their holes and firm them in by gently pressing the soil in around them.
- Water the seedlings generously. It's important to completely wet the soil at this stage, and it helps to avoid transplant shock.
- Place in a part-shade position and check back daily to make sure that the soil isn't drying out or waterlogged.
Direct sowing lettuce seeds
Direct sowing lettuce works best when you can sow the seeds in rows, such as in a cold frame, raised bed, or window box.
Here's a step-by-step:
- Prepare your soil and container. Choose a container that's ideally 8-10 inches deep and at least 8 inches wide. Lettuce likes more drainage than most plants, so it's a good idea to combine a potting mix with vermiculite or sand, and to add in some extra compost. Fill the container up to 3-4 inches below the top.
- Trace a drill (row) in your soil. Lettuce seeds are sown to ⅛ inch deep, so this is more to visually mark the row than it is to create a deep trench for seedlings.
- Place seeds in a row, either spacing each seed about an inch apart or sowing groups of three seeds every 8 inches.
- Lightly press the seeds into place and water them. This ensures good contact with the soil.
- Mark your rows so that you don't forget which variety you planted there.
- Seedlings should emerge in 5-14 days.
- Thin to one seedling every 8 inches once they've grown to a couple of inches tall and have all developed their true leaves.
- Mulch around the seedlings to keep the soil cool and improve water retention. This is especially important in very sunny locations.
- Water thoroughly when the top inch of the soil has dried out. Lettuces don't like dry soil or waterlogged soil, so it's important to give them a deep watering only when you've noticed that the topsoil has started to dry.
Lettuce spacing in containers
Giving lettuce enough space ensures a healthy, flavorful harvest. Planting lettuces too closely together will make the plants compete for nutrients and water, resulting in tougher, more bitter leaves. The lack of airflow in packed containers can also encourage downy mildew and other fungal diseases.
There's some variation in spacing requirements depending on the type of lettuce you're growing:
- Loose leaf lettuce: Space 4-6 inches apart
- Romaine (cos) lettuce: Space 8 inches apart
- Butterhead lettuce: Space 8 inches apart
- Iceberg lettuce: Space 10-12 inches apart
Regardless of the variety, space lettuce rows 10-12 inches apart.
Be sure to double-check your seed packet for more specific spacing instructions for your variety.
Growing lettuce plants
Lettuce generally likes full sun, cool weather, and very well-draining soil, but there's some flexibility in their growing requirements:
- Sun: Depending on the variety, lettuce plants can grow in full sun to partial shade conditions. That's as few as 4 hours of direct sunlight to as much as 8 hours of sunlight per day. In warmer zones, placing your containers in a location with afternoon shade can help prevent lettuce from bolting prematurely.
- Soil: Lettuce grows best in very well-draining, rich soil. A sandy or loamy soil amended with compost is ideal. Adding compost or composted manure to the soil before planting can improve soil texture and nutrient content, and adding drainage like sand or vermiculite can ensure the plant can be watered frequently without developing root rot.
- Watering: Lettuce plants require consistent moisture. Dry spells will cause the leaves to wilt, and can contribute to a bitter flavor. Water lettuces thoroughly when the top inch of soil feels dry. In containers, this will likely be more often than it would be for in-ground or raised bed plants.
- Fertilization: Lettuce grown in rich soil in sizable containers shouldn't need additional fertilization. But if you do notice signs of nutrient deficiency, consider supplementing the soil with an organic fertilizer like garden compost, compost tea, comfrey tea, or a gentle liquid seaweed fertilizer. If you're using pelleted fertilizer or granules, aim to use one with a balanced NPK ratio.
- Mulching: A couple of inches of mulching with straw, compost, dried grass clippings, or shredded dried leaves helps the soil to stay cool and retain moisture.
Harvesting lettuce
Lettuces can be ready for harvest anywhere from 25-80 days from sowing, depending on the variety and whether you want to harvest the entire plant or just the outer leaves. Here's a breakdown of how and when to harvest lettuce by type:
- Loose leaf lettuce: This includes individual loose leaf varieties as well as mesclun and salad mixes. Most loose leaf varieties reach maturity at 6-8 inches tall, but the outer leaves can be harvested at any time once the plant is established. Some mesclun lettuces reach only 4-6 inches tall, but they're harvested in the same way. For multiple harvests of loose leaf lettuces, pick or cut off the outer leaves, breaking them from the stem 1-2 inches above the soil level. Alternatively, you can harvest the whole plant at once by cutting the entire stem down to 1-2 inches above the soil.
- Romaine (cos) lettuce: Cos lettuces have an upright growth habit and can be harvested anywhere from 6-10 inches tall, or after approximately 25-60 days. As with loose leaf varieties, you can harvest off of one plant multiple times by removing the outer leaves, or you can wait for the plant to mature and cut it all the back.
- Iceberg (crisphead) lettuce: Crisphead lettuces that are very compact take longer to mature-- as much as 60-80 days from sowing. At that point, check to make sure that the plant has formed a dense, compact center by squeezing it slightly. Iceberg lettuces are best harvested all at once by using a sharp knife to cut the stem down to the soil.
- Butterhead lettuce: Like loose leaf lettuce, butterhead varieties can be harvested after at least 20 days from sowing and should reach maturity within approximately 60 days of sowing. There's a wide range in their growth habits-- some varieties can reach 8 inches tall, while others may only grow to 3-4 inches tall. You can harvest them multiple times in a season by cutting the outer leaves from the stem 1-2 inches above the soil.
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