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Lettuce Growing Guide

Rouge d'Hivers Lettuce
Rouge d'Hivers Lettuce - Glorious colors and impeccable resistance to cold

 

All the plants we call lettuce have the same scientific name: Lactuca Sativa. They are members of the Asteraceae family, also known as the Compositae family, which is the same as other well known plants such as Asters, Daisies and Sunflowers. 

Despite the fabulous array of colors, flavors, shapes and textures, all the lettuces have the same general growing requirement. This is fantastic news for the gardener, who can master the growing of lettuce and fill his garden with a never ending rainbow of colors and flavors for every season. 

All you need to know to grow great lettuce is contained in this easy to read and master growing guide. So keep reading on and "lettuce grow"!

 

 

How to Sow and Plant

Lettuce may be grown from seed sown indoors and transplanted outside as soon as 3 weeks before the last frost sown directly in the garden as soon as the soil can be worked at about the same time. Lettuce plants can also be kept as potted specimens, either indoors or outdoors.

 

Growing Guide at a Glance - Lettuce

Sowing Seeds Indoors

Lettuce plants are one of the easiest to grow from seeds and even the beginner gardener can sow his own transplants indoors. The plants are easy to transplant when young and easily establish.

Sow lettuce seeds indoors 6-8 weeks before the average last frost date in spring using a seed starting kit.

Sow seeds ¼ inch deep in seed starting formula. Do not plant too deep and do not compact the growing medium. 

Keep the soil moist at 70 degrees F

Seedlings will emerge in 7-10 days

As soon as lettuce seedlings emerge, provide plenty of natural light on a sunny windowsill or grow under fluorescent light on a 12 hours cycle.

Transplant lettuce seedling in the garden after a period of “hardening”, increasing the seedling’s exposure to sunlight gradually over a one-week period. Seedlings are ready for transplants when they have 3 to 4 true leaves. 

Lettuce seedlings ready for transplant
Lettuce seedlings ready for transplant - Lunix Lettuce and Rouge D'Hivers Lettuce pictured here 

 

Do not allow lettuce plants or seedlings to dry out completely until well established.

Sowing Seeds Outdoors

Direct sow in average soil in full sun as soon as 3 weeks before your last frost date. Slower germination will occur with lower temperature.

Young healthy lettuce plant
Young healthy lettuce plant sown directly outdoors in early Spring

 

Sow seeds evenly and cover with ¼ inches of fine soil. If you want to grow leaf lettuce, sow then in thick bands spaced 8 inches apart. Head lettuces should be sown 6 inches apart. 

Firm the soil lightly and keep evenly moist.

Seedlings will emerge in 7-10 days.

Thin to 6-8 inches apart when seedlings have three pairs of leaves if you want to grow head lettuce. Thin to 2-3 inches apart for a thick mat of leaf lettuce or leave thickly sown and harvest at the baby green stage.

 

How to Grow

Select a location in full sun to partial shade and well-draining soil.

Do not allow the plants to suffer drought. Plant or sow directly in average, well-draining garden soil and keep free or weed competition.

Lettuce does not need overly fertile soil, but a nitrogen deficiency will result in a poor harvest of leaves.

Lollo Rosso Lettuce
Lollo Rosso Lettuce - Cold hardy and fast to grow, a real crowd pleaser!

Lettuce grows quickly and is easy to grow in containers. If your space comes at a premium, then lettuce is a great choice. 

Tips for Greatest Yield

There are many ways to obtain a great lettuce yield. Of course, you can harvest entire plants by cutting them off at the base, just as you would see in a grocery store. Few home gardeners opt for this method as it is the least efficient in terms of space and yield. It is however the preferred method for large to medium scale growers and consumers have gone accustomed to see entire heads of lettuces in their grocery carts. 

The second methods and the most often used by home gardeners can easily be described as a "cut and come again" leaf mat. In this method, lettuce seeds are broadcasted either in rows or over a rectangular area and left to grow in a thick, weed suppressing mat. Then, the gardener harvests sections of the lettuce  row or mat at the baby leaf stage, being careful not to cut the main stem of the plants. Alternatively, the gardener can come and harvest individual leaves in this thickly growing lettuce carpet. This method works well but tends to send the plants to seed earlier, as soon as  the plants are stressed by heat or drought. 

 The last method and our favorite is to grow head lettuces, spaced at 6-8 inches on center and harvest the bottom leaves as the plant  grows. This leaves a strong, healthy plant and that is capable of pumping more leaves as it grows. Since the plants are hardier and stronger when given more space, they are also more resistant to bolting and will endure longer in the heat or partial drought before going to seed. 

In the end, though, all lettuce plants will go to seed. This is their natural lifecycle and cannot be stopped. As soon as the flower head develops, the flavor of the lettuce will turn bitter and unpleasant. If this happens, do not worry and do not try to solve the problem by adjusting your growing practices. Simply pull out the plant or plants and resow or plant a new transplant in its place. 

Thus is the lifecycle of Lactuca Sativa! Its entire goal is to produce seeds to ensure that the next generation grows and propagates its genetic material. 

Alternatively, you can see your flowering lettuce as an opportunity to harvest your own seeds and let the plant complete its cycle. Read on for lettuce seed saving tips. 

 

 

Lettuce Seed Saving Instruction

 Lactuca Sativa is an inbreeding plant and thus will be true to itself without the help of a pollinator. 

Lettuce flower heads
Lettuce plants gone to seed - when the flowers are "puffs" are ready for harvest

 

As a general rule, lettuce plants are so strongly inbreeding that there is no need for isolation of any kind when saving seeds from an open-pollinated variety. It is recommended that plants grown for seed saving purposes be isolated by at least 25 feet from other Lactuca Sativa plants to ensure seed purity. 

For home gardener concerns, there is little to worry about, though. You can consider your seeds pure if you take care not to plant them too close to another lettuce and call it a day. 

To save your lettuce seeds, allow the plant to go bloom. Lettuce flowers are wildly attractive to a wide range of pollinators and make for a beautiful and unusual display. 

Wait until the lettuce blooms have turned into "puffs" before harvesting the seeds. Simply cut the tip of the bloom on a dry day and rub it between your fingertips. The tiny seeds are easy to detach but be warned - they are so light that they will readily fly away at the slightest breeze! 

There is no more processing needed. Simply thoroughly dry the seeds and store in a cool, dry place away from sunlight until you want to plant the next succession of lettuce. 

Common Disease and Pests

Downy Mildew

Causes: Fungal infection. Mature leaves are often most affected by this disease.

Symptoms: Lettuce develops a yellow area on the upper side of the leaves and a white or gray fluff on the underside.

Solution: Remove infected plants and plant debris, clean tool before and after working with diseased plants. Ensure good air circulation between plants.

Leaf Spot

Causes: Bacterial infection. Mature leaves are often most affected by this disease. The pathogen, Xanthomonas campestris pv. vitians, is highly dependent on wet, cool conditions for infection and disease development. 

Symptoms: Lettuce develops brown spots on mature and immature leaves.

Solution: Remove infected plants and plant debris, clean tool before and after working with diseased plants. Ensure good air circulation between plants.

Lettuce Mosaic Virus

Causes: Viral infection. Lettuce mosaic virus is transmitted by several species of aphids and by 1 to 8% of the seed produced by infected plants. Plants infected through the seed are the main source of virus for its subsequent transmission by aphids to other plants.

Symptoms: Wrapper leaves affected by lettuce mosaic virus may appear dull, are folded backward, and may have more marginal serration. Romaine lettuce leaves typically show the same symptoms in addition to leaf blistering. Butter head lettuce experiences stunting and severe chlorosis.

Solution: Remove infected plants and plant debris, clean tool before and after working with diseased plants. Ensure good air circulation between plants.

Bottom Rot

Causes: Fungal infection. Bottom rot is caused by the soil-borne fungus Rhizoctonia solani, and is a naturally occurring fungus. Infection occurs when sclerotia (dormant resting structures) germinate and produce mycelium that penetrates healthy or wounded tissue. Affected plants are usually tightly packed  head lettuces grown in hot and humid weather.

Symptoms: Bottom rot generally affects iceberg, Boston, and Bibb varieties of lettuce and can be observed during warm, humid weather. Lettuce suffering from bottom rot usually loses a couple of wrapper leaves.

Solution: Remove infected plants and plant debris, clean tool before and after working with diseased plants. Ensure good air circulation between plants.

Bacterial Diseases

These diseases include bacterial corky root rot, bacterial soft rot, and a number of diseases that can affect roots, leaves, and even the entire plant.

Solution: Remove infected plants and plant debris, clean tool before and after working with diseased plants. Ensure good air circulation between plants. 

Slugs

Symptoms: Leave large holes in the foliage or leaves missing entirely. Slime trail left on leaves and stems. Slugs cause defoliation and can kill young plants with intense feeding. They mostly feed at night. Moist weather increases their presence.

Causes: Pest infestation.

Solution: Hand pick, at night if possible. Use slug traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent of cornmeal, but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.

 

Common Problems

Bitter, unedible leaves:  Caused by the plants going to seed. This is a normal part of lettuce growing. Lettuces are an annual plants that will go to seeds in their first year. The bitter compounds are a protective strategy of the plant as it tries to deter predators from eating it before it can produce mature seeds. When the flavor turns bitter, simply pull out the plants and sow new seeds.

 

Lactuca Sativa varieties carried by Ethos Seed Company. 

 

References:

Lettuce Disease Management, University of Florida

UC-IPM, Lettuce Pest and Disease Management