Lettuce: Answers to Frequently Asked Questions About Growing Lettuce, Storing Lettuce, and Preparing Lettuce

Red Looseleaf Lettuce, Image Courtesy of Panpote, FreeDigitalPhotos.net
Red Looseleaf Lettuce, Image Courtesy of Panpote, FreeDigitalPhotos.net

There are four types of lettuce: looseleaf, crisphead, butterhead (Bibb), and romaine (Cos).

Looseleaf types, which do not form heads, are the easiest to grow, the most tolerant of high or low temperatures, fast-maturing, very nutritious, and available in a wide variety of colours and sizes.

Butter Lettuce, Image Courtesy of Feelart, FreeDigitalPhotos.net
Butterhead Lettuce, Image Courtesy of Feelart, FreeDigitalPhotos.net

Butterhead lettuces (such as Buttercrunch) form rosettes of tender leaves gathered into a loose head. They are also easy to grow, but they take longer to mature than looseleaf varieties.

Iceberg Lettuce, Image Courtesy of SOMMAI, FreeDigitalPhotos.net
Iceberg Lettuce, Image Courtesy of SOMMAI, FreeDigitalPhotos.net

Crisphead types such as Iceberg, which form tight, firm heads, require a longer period of cool weather and are among the most challenging to grow. They are  also among the least nutritious, but continue to be popular for their crisp texture and the fact that they stay fresh for longer after harvesting.

Romaine Lettuce, Image Courtesy of SOMMAI, FreeDigitalPhotos.net
Romaine Lettuce, Image Courtesy of SOMMAI, FreeDigitalPhotos.net

Romaine lettuces, which are the most nutritious, form elongated heads of crisp leaves. They require more time to reach maturity than looseleaf types.

Other salad greens that will grow in similar conditions to lettuce include arugula (also known as rocket), endive, mache (also known as corn salad or lamb’s lettuce), spinach, kale, Swiss chard, winter purslane (also known as miner’s lettuce), chicories such as radicchio, and mesclun mixes. Mesclun is actually a collection of different types of salad greens, which typically include one or more types of lettuce, along with one or more additional greens, such as arugula, chervil, cress, dandelion, endive, radicchio or other chicories, purslane, mache, mizuna, orach, komatsuna, and others.

Arugula, Image Courtesy of Apolonia, FreeDigitalPhotos.net
Arugula, Image Courtesy of Apolonia, FreeDigitalPhotos.net

Lettuces come in a variety of colours, ranging from shades of green to deep reds and purples, and some varieties are variegated, with attractive patterning. Lettuces are also available in various shapes, ranging from flat-leafed to elaborately frilly.

Lettuce is a great source of dietary fiber, and very low in calories, so it’s a great diet choice. The nutritional content of lettuce varies, based on the type, with different lettuce varieties containing different amounts of minerals, vitamins, and other health-promoting nutrients.

Lettuce grows best in moist, cool conditions. In hot, dry conditions, it will quickly turn bitter and bolt (start producing flowers and seeds). However, if you provide shade during the hottest part of the day and a cold frame or greenhouse in the winter, it’s possible to grow lettuce year-round in many areas.

When can I plant lettuce?

Lettuce will germinate in temperatures ranging from 35-80 Fahrenheit/2-27 Celsius (though in hotter temperatures, many lettuce seeds will not sprout). Ideal growing temperatures range from 60-65 Fahrenheit/15-18 Celsius, but lettuce will grow in a range from 45-75 Fahrenheit/7-24 Celsius (however, it’s quick to grow bitter and produce flowers at temperatures above 65 degrees).

If you’re sowing your lettuce directly outdoors, plant your leaf lettuce 4-6 weeks before the last anticipated frost date and head lettuce 2-4 weeks before the last frost date (you can start a little earlier if you provide cold protection, such as a cold frame or cloches). Then succession sow every 2-3 weeks for a continuous crop, but provide partial shade for summer crops if you’d like to try growing your lettuce throughout the seasons. For a fall lettuce crop, plant 6-8 weeks before the first frost date.

It can be challenging to start a fall crop of lettuce because the seeds are planted in the summer, when temperatures are still quite warm, which discourages germination. Some gardeners increase germination rates by pre-chilling lettuce seeds, which can be done by placing them in a sealed plastic bag with a bit of moist potting soil and storing them in the fridge for a week.

If you want to start your lettuce indoors to get a head start on the growing season, you can begin your transplants 6-8 weeks before the last frost date and then plant them out 2-4 weeks before the last frost date (both leaf and head lettuce).

Where should I plant lettuce?

Plant lettuce in a sunny spot in the garden when temperatures are cool, and choose a lightly shaded spot if your lettuce is likely to mature during the summer, or if you live in a hotter climate.

How far apart should I plant lettuce seeds?

Start lettuce seeds 1-2 inches/2.5-5 cm apart, and when the plants are 2-4 inches/5-10 cm tall, thin them out to the spacing you require (this will vary based on whether you’re growing the lettuce for baby greens or want to let it reach full size). You can eat the thinnings.

Spacing for full-sized lettuces is approximately 9 inches/23 cm between plants. If you’re growing medium-sized lettuces rather than large lettuce heads, they’ll only need to be 6 inches/15 cm apart, and 3 inches/8 cm is sufficient for cut-and-come-again greens (leafy greens that provide a continuous harvest when you regularly remove the outer leaves while allowing the younger inner leaves to continue maturing).

If you’re growing lettuce in rows, leave at least 6 inches/15 cm between them for leaf lettuce and 10 inches/25 cm for head lettuce. If you have a square foot garden, you can grow approximately 4 full-sized lettuce plants per square foot.

How long will lettuce seeds take to sprout?

The time lettuce seeds require to germinate varies based on temperature. They sprout within days in warmer temperatures and may take weeks in cooler temperatures (though if temperatures are too warm to too cold, they may not germinate at all).

What type of soil does lettuce need?

Lettuce will grow best in a soil that is fertile, well-drained, rich in organic matter (compost), and moisture-retentive. Add compost or aged manure to the soil before planting, as these are good sources of nitrogen, the most important requirement for lettuce because it’s a leafy vegetable, and nitrogen promotes lush leafy growth. Dig these amendments into the first few inches of soil (lettuce is shallow-rooted, so there’s no need to dig deep).

Can I grow lettuce in a container?

Lettuce does well in containers because it has shallow roots. Containers for growing lettuce should be at least 6 inches deep, unless you plan to harvest the leaves very early as microgreens.

The best types of lettuces for container growing are cut-and-come-again looseleaf varieties and small head lettuce varieties such as Tom Thumb, which was developed for smaller urban gardens.

Containers provide the added benefit of mobility, so you can move them to cooler spots in the garden when temperatures grow warmer. However, the soil dries out more quickly in containers, so you’ll need to check them every day and water as needed. Also, soil fertility is even more important when growing in a smaller space.

Can I grow lettuce in the shade?

Lettuce is more shade-tolerant than most food plants, and will usually do fine in partial shade (just a few hours of sun per day), particularly if temperatures are high.

Should I fertilize my lettuce plants?

If you’re starting with nutrient-rich soil that has been enriched with good compost, you may not need to add anything. However, if your soil is nutrient poor, adding some compost tea or liquid kelp approximately one month before harvest can be beneficial, or purchase a nitrogen-rich fertilizer from a garden center.

What ongoing care does lettuce need?

Weed regularly, especially when the plants are young, as they don’t compete well with weeds.

Keep the plants well-watered and the soil consistently moist. If the soil dries out, your lettuce will turn bitter. Mulching can help to conserve moisture, prevent weed growth, and keep temperatures down during the warmer months.

If you see any aphids on your lettuce leaves, spray them off with a blast of water from a hose.

How long does lettuce take to grow?

The time to maturity varies significantly from one type of lettuce to the next, ranging from a little over a month to several months. Looseleaf lettuces reach maturity in 45-60 days, butterhead lettuces require 55-70 days, Romaine lettuces require around 70 days, and crisphead lettuces need 75 days or more.

When do I harvest lettuce?

Leaf lettuce can be harvested at any stage before it bolts (produces a flower stalk) and turns bitter. You can harvest very early for microgreens, a bit later for baby greens, or let the plants reach maturity.

Head lettuce is typically left to mature until the heads are fully formed, though you don’t need to wait until they reach full maturity. With lettuce, it’s always best to harvest earlier rather than leave it too late, as it will quickly grow bitter if left in the ground too long.

Ideally, you should harvest lettuce on the day you plan to eat it. You can take the whole plant or harvest some of the leaves, as needed.

Why didn’t my lettuce seeds sprout?

There are a number of reasons why lettuce seeds won’t germinate, including temperatures that are too hot or cold, allowing the soil to dry out, and using seed that is more than a year old. Lettuce seeds may also be eaten by birds.

Why does my lettuce taste bitter?

Hot temperatures and dry soil are the most common causes of bitter lettuce. Lettuce will also become bitter once it bolts (produces a flower stalk).

Why did my lettuce seedlings die?

Fungal diseases such as damping off can kill lettuce seedlings. The cause is usually overcrowding or a spell of cold, damp weather.

Why are my lettuce leaves full of holes?

Slugs and snails can quickly chomp their way through a lettuce crop, leaving it full of holes or even causing it to disappear altogether overnight. See Natural Garden Slug Control for non-toxic solutions to slug and snail problems.

Cutworms are another common pest in the lettuce patch. Some gardeners protect their plants with cutworm collars, which can be purchased or made from scrap cardboard, plastic, or tinfoil.

Deer, groundhogs, and rabbits may also eat your lettuce. In this case, fencing is required to protect the crops.

Why are the tips of my lettuce leaves turning brown?

Tip burn is a common problem in lettuce. It’s usually caused by fluctuations in moisture, especially when temperatures are high. You can prevent this problem by keeping the soil evenly moist.

Lettuce Producing Seeds
Lettuce Producing Seeds

Why did my lettuce produce flowers early?

Lettuce will often bolt early due to hot temperatures or overcrowding. Once the plant has bolted, it won’t taste good anymore.

To reduce the risk of early bolting, grow bolt-resistant varieties and provide shade during the hottest part of the day when temperatures are high.

How do I store lettuce, and how long will it keep?

Leaf lettuce will keep for up to a week in a plastic bag in the refrigerator, and head lettuce will keep for several weeks when stored the same way. However, both types will have the best flavour if you eat them as soon as possible after harvest. Don’t wash the leaves until you plan on consuming them.

Lettuce can be frozen, but this destroys the texture, so it will be no good in salads. Frozen lettuce can be used in soups and quiches, but not any dish in which it is uncooked.

How do I save seeds for lettuce?

Left to bolt, lettuce will produce pretty flowers, followed by fluffy seed heads that look similar to small dandelion seeds. To collect the seeds, hold a paper bag over them and shake. You may have to do this every few days, as lettuce seeds don’t ripen all at the same time.

Another collection option is to cut off the entire stalk when half the seed has ripened and finish drying it in a paper bag. Once this is done, remove the fuzz and store the seeds in a cool, dry place.

Different lettuce varieties can cross-pollinate, so separate them by at least 25 feet.

It’s best to use lettuce seed within a year of collecting it, as germination rates drop significantly once the seed is more than a year old.

How do I prepare lettuce?

Lettuce is most commonly chopped (or added whole as baby greens) to salads, sandwiches, wraps, and burgers, but if you’d like to do something more creative with your lettuce, there are some great lettuce recipes available online. See The Kitchn’s Help! Ways to Use Lettuce Besides Salads and Sandwiches? You can also find a mix of gourmet salad and non-salad lettuce recipes on The Guardian’s 10 Best Lettuce Recipes page.

For more vegetable and herb gardening articles, see the main Gardening page.

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