Learn About Lettuce
Why did my lettuce seed not germinate? Lettuce seed needs some exposure to light in order to germinate. This means they should be sown and covered very lightly so sunlight will penetrate the soil but there is enough soil to protect the seed.
Why won’t my iceberg lettuce form a head? Iceberg lettuce requires an unusually long cool season (for a lettuce) to form a tight head. Any warm weather or moisture stress during development will cause a misshapen head, incomplete head or no head. Another possibility is that the plants are growing too closely to one another. Crowding causes plant stress.
Why did my lettuce produce a tall stem and flower? The lettuce was exposed to warm weather or moisture stress prematurely OR lettuce plants were not thinned enough.
My lettuce is very bitter (inedible). Why? Always harvest in the earliest part of the morning just before the sun rises if possible. This is when all the lettuces taste their best. Once a stem starts to grow taller, the lettuce plant becomes bitter, tough and undesirable as an edible green.
Can I grow lettuce inside or hydroponically? Yes, leaf types of lettuce may easily be grown inside under lights. It’s a great plant for hydroponics.
Common Disease Problems
Bacterial Leaf Spot: This causes brown water soaked spots on the foliage which eventually makes the foliage turn yellow. It thrives in cooler temperatures. Burpee Recommends: Remove infected plants. Rotate crops with plants in a different family. Avoid overhead watering. Do not work around plants when they are wet.
Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy; then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater; avoid over-fertilizing your seedlings; thin out seedlings to avoid overcrowding; make sure the plants are getting good air circulation; if you plant in containers, thoroughly wash them in soapy water & rinse in a ten per cent bleach solution after use.
Downy Mildew: This fungus causes whitish gray patches on the undersides and eventually both sides of the leaves. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet.
Fusarium Wilt: This fungal disease causes yellowing and stunting of older plants and yellowing, stunting and death to seedlings. The plant will exhibit signs of wilting frequently and the lower leaves turn yellow and dry up. Burpee Recommends: Practice crop rotation. Try to plant resistant varieties.
Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.
Common Pest and Cultural Problems
Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps which feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Cabbage Looper: These worms are green with a white stripe on either side, about 1-1.5 inches long. They tunnel through the heads. Burpee Recommends: Hand pick. Floating row covers can help prevent their laying eggs on the plants.
Flea Beetles: These small hopping beetles feed on plant foliage. Burpee Recommends: Rotate crops with plants in a different plant family. Use floating row covers to prevent damage to young foliage.
Leafminers: These insects bore just under the leaf surface causing irregular serpentine lines. The larvae are yellow cylindrical maggots and the adults are small black and yellow flies. They do not usually kill plants, but disfigure the foliage. Burpee Recommends: Remove affected foliage.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to 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 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.
Harvest and Preserving Tips
- For the best quality, pick lettuce early rather than late as lettuce allowed to grow too long may be bitter and tough.
- Try to harvest in the morning when the leaves are crisp, sweet, and full of moisture.
- Harvest looseleaf types anytime the leaves are large enough to use.
- Harvest butterhead types when they have formed heads and the leaves are a good size.
- Cut the heads below the crown.
- On leaf types, you can just pick a few leaves at a time, if you like.
- Store for 5-7 days in a plastic bag in the refrigerator. Many gardeners wrap leaves in moist paper towels.
- Lettuce is a classic ingredient in salads. It adds crispness to sandwiches and can be used as a garnish, braised, or added to soups. Many of the looseleaf cultivars are also decorative in the garden.
How to Grow
- Thin to stand 8 inches apart when seedlings are 1-2 inches tall.
- Keep lettuce plants well watered during dry periods to promote rapid, uninterrupted growth.
- Lettuce is shallow-rooted, so avoid disturbing the soil around the plants when weeding.
- Unless there is regular rainfall, lettuce plants must be watered deeply at least once a week and more frequently during periods of drought.
- Mulch with a layer of compost or clean straw to help the soil retain moisture.
How to Sow
- Sow lettuce seeds in average soil in full sun in early spring for first crop. Sow in late summer for fall crop.
- Sow every two weeks to extend harvests.
- In late summer, sow in a protected are that stays below 75 degrees F.
- Sow thinly in rows 12 inches apart and cover with ¼ inch of fine soil.
- Follow the spacing recommended on the seed packet for specific varieties.
- Firm lightly and keep evenly moist.
- Seedlings emerge in 7-10 days.