Who doesn’t love lettuce? Seriously, salad is a staple on our kitchen table pretty much every night. Mixed in with some delicious onions, peppers, tomatoes, maybe some mushrooms, topped with a yummy homemade salad dressing.
Mmmmmm….my mouth is watering just thinking about it!
Lettuce is a high-yield, high-rewarding crop that is fairly simple to grow.
Sounds great, right? Well, it is!
There are five different types of lettuces, suited for various tastes and situations.
The bolt resistance generally goes from leaf types (first to bolt) through romaines and butterheads, to icebergs, with Batavians as the best, apart from Jericho and Kalura romaines.
Leaf lettuce includes the more familiar Oak Leaf types and very frilly ones that add interesting texture and appearance to mixes as well as important “loft”, which prevents mixtures from falling into unpleasant flat heaps.
Leaf lettuces are usually the quickest to produce harvestable-sized leaves and in general, have more heat tolerance, but not bolt resistance, than romains.
Despite the name, leaf lettuce can be harvested as a whole plant, not only leaf by leaf for mixes.
Romaines (cos) Lettuces
Romaine lettuces are upright, usually green, often very crisp and flavourful.
They have double the vitamin A and C of other kinds of lettuce.
Butterhead (Bibb, Boston) Types
These lettuces are usually grown as full heads. They are high in vitamin A, folacin, and fibre.
The Bibbs, which have soft sweet tender leaves, can be used at the baby stage in mixes.
Iceberg lettuce is usually grown as full heads and is less useful for leaf lettuce mixes.
They have high water content and are less nutritionally dense.
Also called summer crisp or French crisp, Batavian lettuces are tasty, thick-leaved varieties that have excellent heat and cold tolerance.
Batavian varieties also have particularly good hot weather germination.
Lettuce Varieties for Spring and Summer
Some standards like the Salad Bowls are available year after year. Others can be in fashion for a few years and then disappear.
In the spring, on Pam’s farm, they grow:
- Green Forest
For summer, they grow:
- Jericho and Kalura romaine lettuce
- Batavians such as:
- Anuenue is the only iceberg they grow in summer
Curtis Stone grows the following varieties:
- Red and Green salad bowl
- Oak leaf
- Rouge D’hiver
- Red sails
JM Fortier and team grow:
- Salada Bowl (red and green)
- Grand Rapids
Lettuce seed remains dormant unless triggered by adequate light and warmth.
It needs light to germinate, so don’t sow too deep:0.25”- 0.4” is enough.
The optimum temperature range for germination is 68-80°F (20-27°C).
Germination takes seven days at 50°F (10°C), four at 59°F (15°C), three at 68°F (20°C), only two days at 77°F (25°C), back up to three at 86°F (30°C) and will not occur reliably at hotter temperatures.
Even a few hours at temps higher than the optimum can induce dormancy, so store seed in a dark, cool, place. In summer, refrigerate between sowings.
Lettuce prefers a well-draining soil high in organic matter, with a pH of 6 to 7, not lower.
Fertile soil with good tilth is essential, to allow a good root system to develop.
The roots also need air exchange, so do not let the soil get crusted.
Lettuces need to keep growing fast to taste good.
Optimum growing temperatures are 60-65°F (15-18°C), with a minimum of 40°F (4.5°C) for growth to occur.
If nights are cool 80-85°F (27-29°C) days can be tolerated.
If temps are too hot, lettuce will bolt, although some varieties are a lot more heat-tolerant than others.
Lettuce is more cold tolerant than many people realize.
Outdoors, a combination of cold nights, chilly days, and wind damage will eventually kill them.
Lettuce requires a large amount of water throughout its growth.
Insufficient water is the main cause of bolting and/or bitterness. Bolting is also more likely with long days, mature plants, poor soil, crowding, and hot weather.
Lettuce for mature heads can be direct-seeded whenever the weather is suitable, or it can be transplanted.
Some growers like to use pelleted seeds for direct sowing as it is easier to space the seeds as needed.
For raw seed, sprinkle thinly in a shallow drill.
The minimum soil temperature for germination is 35°F (1.6°C).
Emergence takes fifteen days at 41°F (5°C), seven days at 50°F (10°C), and three days at 68°F (20°C).
Direct seeding is used for growing baby lettuce mix, which is cut when small and then allowed to regrow for further cuttings.
Mesclun, salad mix, spring mix, and misticanza are all names for mixtures of baby lettuces, sometimes with other greens.
Cells with diameters from 1 to 21/2” can be used.
The 96 cell (1”x1 ½”) size works well as does the 200 cell size (1”x1”) if you can be sure to get the transplants out before they get root-bound.
If warm germination space is limited in early spring, sow seed in a small flat, then spot the tiny seedlings into bigger flats or 606 cell packs (2”x2 ¼”) to grow in cooler conditions before planting out.
Soil blocks are also possible but take more time.
It is recommended to sow several different varieties each time, not only for the beautiful effect but also to spread your risks in case one kind of lettuce bolts or suffers disease.
Another option, from mid-April to October, is to use an outdoor nursery bed rather than sowing in flats.
You simply sow at 3-foot rows for each final planting of 120 lettuce.
Water, weed, then transplant the bare-root plants directly from the seedbed.
In very hot weather, indoor sowings might give more reliable germination.
Fall crops to be finished in a hoophouse or other protected structure can either be direct sown or transplanted as bare-root seedlings from an outdoor nursery bed or from plug flats.
Because conditions in a hoophouse can be warmer than ideal for lettuce germination until well into fall, it often works better to start plants in a cooler location, then move the plants.
Curtis Stone takes the approach of direct seeding, planting almost weekly during the main season.
He grows between 5 and 6 varieties of loose lettuce that do well in his climate, and all have the same date to maturity (DTM).
This way, he can mix the seeds together and plant them all in the same bed.
The varieties he grows have changed over the years, and change throughout the season.
Just make sure you’re growing varieties that all have the DTMs that are within a few days of each other so the harvest is consistent.
JM and team have developed a planting schedule where they start new seedlings every 15 days, each time choosing two cultivars with different growing periods, for example, 45 and 52 days respectively.
This takes the guesswork out of succession planting and makes certain that they will have staggered lettuce crops.
When doing their starts, especially early in summer, they plant 30% more seedlings than necessary, a safety factor that offsets any unforeseen germination or plant failures at the transplanting stage.
Transplanting lettuce offers several advantages, including:
- The ability to grow lettuce when outdoor temps don’t favour germination.
- Getting a jump on weeds by eliminating the need to weed around seedlings.
- There is time for another crop to mature in the space while transplants are growing, increasing overall yield.
- In early spring, an earlier harvest is more possible from transplants than from a direct-seeded crop, since the transplants grow indoors while it is too cold to direct seed.
- Transplants are tougher than seedlings in withstanding some pests and fungal disease.
Transplant the seedlings at 3-6 weeks of age (4-6 true leaves) depending on the time of year and how fast they are growing.
Early in spring, plants will take a long time to size up.
As the weather warms they will grow more quickly until it gets hotter than ideal for them.
Handle transplants only by their leaves or the rootball, try not to damage the roots or stem.
Transplant seedlings 8-12” apart, firm them in and water.
Use the 12” spacing outdoors for growing full-sized heads, and the closer spacing if you will be harvesting individual leaves.
Watering in with seaweed solution helps plants recover from transplant shock.
Tools to speed transplanting and increase spacing accuracy include:
- measuring sticks or plywood triangles
- transplanting wheels
- row-marker rakes
- pre-set drip irrigation tape run for 15-20 minutes before planting, to make wet spots to plant into (accurate spacing saves a lot of time at cultivation)
Curtis uses landscape fabric with holes burned in at 6” centers, then transplants the lettuce in the holes.
Keep in mind he grows predominantly loose lettuce for salad mixes so he does not require a ton of spacing.
In warm weather, lettuce can be ready to harvest 4 weeks after transplanting, as baby heads or as individual leaves, and six weeks after transplanting as full-size heads.
In summer, heads can be ready in as little as three weeks from transplanting.
Water new transplants daily for the first 3 days, then only once or twice a week after that.
Deeper weekly water is equivalent to an inch of rain is better than frequent superficial irrigation, as roots will grow deeper, giving the plant greater resistance to drying out.
Caring for Lettuce
Hoeing or tractor cultivation will likely be needed to remove weeds, as these compete with the crop and could get mixed in at harvest.
All cultivation should be shallow, as lettuce roots are near the surface.
Crop rotations including cover crops can do a lot to reduce the weed problem.
Lettuce requires a relatively large amount of water throughout its growth.
In cooler weather, water late morning or early afternoon, giving the leaves time to dry before sunset.
This reduces the chance of fungal diseases.
Spraying with seaweed extract can double the size of lettuce in one to two weeks, enabling harvest up to three weeks earlier.
Pests and Diseases
Organic growing involves using the least invasive methods of pest control.
Grow the crop in ways that are least likely to encourage pest outbreaks.
Maintain balanced soil fertility, irrigation, airflow, daylight, temperature, and growing space.
Farmscape to encourage beneficial insects, including predators of pest bugs.
Use foliar feeding to boost the plant’s growth and health.
Row cover or netting can keep insects from eating your crop.
Monitor crops for pests regularly look closely and record any outbreaks, the level of infestation, and controls used. This will provide useful information for future years.
Small numbers of pests may not be doing enough damage to worry about.
Once the number of pests exceeds the “Action level”, start with the method that will cause the least damage to other life-forms.
Often this is physically killing or removing the pest: hand-picking, vacuuming, or forcing them off with a jet of water.
If the scale of the outbreak is too large for physical controls to work, the next stage can be to introduce beneficial insects, either relocated from elsewhere on your property or purchased.
When an infestation is too large and the rate of increase is too fast for predatory species to manage, it becomes necessary to use some kind of insecticide to save the crop.
Some Botanicals also kill beneficial species, so if you plan to use those, do not introduce the beneficials until after the pesticide has had time to reduce the numbers of infestation, and to degenerate.
Here are some specific management strategies for pests and diseases you may encounter.
Aphids: Farmscape with alyssum, clover, dill, or yarrow.
Use row cover, but check aphids have not got in you may only be keeping the predators out.
Water jets, insecticidal soap, horticultural oil, hot pepper wax, flour, diatomaceous earth, or other desiccants are also useful for managing aphids.
Aphids thrive at lower temperatures than most of their predators, so they are a special problem in early spring before temps reach 45°F (7°C).
- Trap in sunken plastic dishes of beery sugar water
- Use Sluggo bait
Grasshoppers and crickets: Use bait containing the parasitic Nosema locustae.
The praying mantis is a predator to grasshoppers and crickets also.
Cutworms: Dig gently near plant stems, catch and kill.
Alternatively, you can use sulfur, or collars around each plant.
Thrips: Try rowcovers, sugar esters, insecticidal soap.
Introduce predators such as, pirate bugs, lacewings, ladybugs.
Flea beetle: Can ruin a crop if not kept under control.
Breaking up plantings of Asian greens with lettuce is generally enough to interrupt the pest’s life cycle, but you can still cover the beds with row covers or insect nets immediately after seeding as an added protection.
Regular inspections of your lettuce crops are also recommended because you can actually trap the flea beetles inside the netting and have to use an insecticide to get rid of them. Vigilance is key.
Groundhogs, rabbits, deer: Try fencing, deterrents (hair trimmings, carnivore urine, dogs), or trapping.
Damping-off affects young seedlings in cool grey weather.
To avoid, reduce watering in chilly weather, increase airflow, foliar feed with seaweed spray, and compost tea.
To make compost tea:
- combine one part compost with 6 parts water
- leave for one week
- filter and spray.
Use every 5-10 days to prevent damping off, powdery mildew, downy mildew, Anthracnose, botrytis, moths, and late blight.
Sclerotinia fungi attack lower leaves at soil level and produce a cottony growth.
The whole plant then collapses flat and limp, with leaves spread out around the collapsed stem.
This disease can be difficult in hoophouses where lots of lettuce is grown.
Soil solarization every fourth year, preferably including biofumigation with a mustard cover crop, is the cure.
Sow the mustard when you transplant the last lettuce crop for that bed in spring.
Cut the lettuce, let the mustard grow a couple more weeks, then turn it under. Late June is ideal.
Irrigate, cover the soil tightly with old hoophouse plastic and cook for 2 months.
Bottom rot, caused by Rhizoctonia fungus, is another soil-born cool-season problem.
It affects fairly full-grown plants, appearing initially as rusty, slightly sunken lesions, perhaps with amber ooze.
The whole plant may rot into a slimy black mess. Use solarization.
Tip burn is a physiological disorder rather than a disease.
It occurs when a sudden change to warmer breezy weather causes rapid transpiration. This can be caused by mismanaged irrigation or greenhouse ventilation by the grower.
If the transpiration rate is much higher than water uptake rate, the plant cannot get water to the outer edges of the inner leaves, which then brown and die.
It is related to soil calcium deficiency, is worse in very fertile soils, and is a particular problem on those lovely sunny early spring days.
Reduce transpiration by shading and or shielding from the wind.
Consider misting or spraying if this doesn’t seem likely to increase the chance of fungal disease.
If tip burn seems to be a big problem in your location look for varieties with resistance.
In cool weather, leaf types are ready for harvest 50 to 60 days from seeding, 30 to 45 days from transplanting.
Head lettuce needs up to 80 days from seeding or 60 to 70 days from transplanting in spring.
In July head lettuce can take as little as 50 days from seed to harvest.
Baby lettuce can be cut 21 days from spring or summer seeding.
In warm and hot weather, be sure to harvest head lettuce every one to three days to get them before they turn bitter.
Excessive milkiness from the cut stem is a sign of bitterness. You can also test by nibbling a piece of leaf.
Harvest methods depend on the size of the crop and the quantity cut each time.
Whole head to maybe cut with a knife; individual full size or half size leaves may be cut with knife, scissors, or thumbnails.
To harvest baby lettuce, use scissors, shears, or a serrated knife, cutting an inch or so above the soil to preserve the growing point of the plants for regrowth.
JM and team use a handheld electric salad mix harvester powered by a hand drill that cuts the greens at their base.
This allows them to get the job done neatly and quickly, cutting the work by more than 80% (a weekly harvest used to take three people working for 3 hours; now it takes one person less than 2 hours).
They also keep their salad mix of high-quality by not picking greens that have become too thick, too spicy, too coarse, or simply too ugly.
By keeping this high standard, their quality is hard to beat at the farmer’s market.
Lettuce should be cooled as soon as possible, as it rapidly wilts. Refrigerate or immerse in ice-cold water immediately.
Forced air cooling and a cold room with high humidity is a good method for large quantities.
Nylon mesh bags are useful for washing loose leaf crops. Thorough washing before sale or serving is most important.
If aphids are a problem, cover with water and wait a few minutes until they sink.
A salad spinner is an ideal way to dry wash lettuce. An old washing machine, with the agitator removed works for large quantities.
If you wash lettuce in a mesh bag, you can swing it around your head; or set up a plastic laundry basket hanging by ropes from a beam or branch,’ wind up’ the basket with the bag of lettuce inside, then let the unwinding spin out the water.
Sort the crop and return it to refrigeration.
Head lettuce to be sold wholesale is packed in the field unwashed, 22-24 heads in a waxed carton.
There are usually two layers: the bottom layer is packed stems downward and the top layer stems up, which keeps the heads in best condition.
Head lettuce can be held for two weeks at 95% humidity and 30 to 32°F (0°C) if necessary.
While I do not consider lettuce to be ‘low maintenance, I still think it is an awesome crop that you need to be growing if you’re not already.
Yes, it has quite a few pests and diseases attached to it, but with daily vigilance, you can prevent/treat them quickly and not lose a whole crop.
As well, by planting 20-30% more plants than you need, you can have a little bit of breathing room if something goes wrong with one of your crops.
There are so many varieties of lettuce that you can even create your own salad mix by growing different types of baby lettuces.
You can get creative here and create your own brand of salad mix. The sky is the limit!
We are concentrating on different varieties of lettuce for our main crops this year, despite not having any washing facilities set up.
We decided to give lettuce a try after visiting a few farmer’s markets over the summer and noticed that there was not a good source of salad mixes. Radishes, yes, but not lettuce.
I will definitely be updating you on our progress going forward throughout the season and all of our trials and tribulations, as well as successes!
What is your favourite lettuce to grow and why? Lettuce know in the comments below!
Kathy & Jon
your friendly neighbourhood growers