Lettuce

Lactuca sativa (Asteraceae or Compositae family)

Production, Main Crop

---

Soil preparation

• Incorporate compost and plant lettuce in raised beds.
• Total nutrient uptake is 95 lbs. of N, 12 lbs. of P and 170 lbs. of K.
• Apply compost and other amendments based on the results of a soil test.
• Spread lime as needed to increase both the pH and Ca levels. Dolomite lime will also increase Mg levels. Spread gypsum when calcium levels are low but pH is correct.
• A fertilizer company can add OMRI-listed potassium sulfate to compost if it doesn’t have enough K to meet the crop’s needs. If this isn’t possible, spread the correct amount of fertilizer and incorporate it before planting. Alternatively, you can side-dress it during cultivation. Divide the recommended rate of the soil test in half if side-dressing. 

Common recommended fertilizer rates¹

Nitrogen	Phosphorus	Potassium	pH
100	0-160	0-200	6.2-6.5
1Rates are for New York and are from Cornell University’s Nutrient Guidelines for Commercial Vegetable Production (2019). Check the Cornell website for updated guidelines, or consult with local experts for recommended rates outside New York.

Varieties

• New York lettuce variety trial
• 2019 New York romaine variety trial: summary and report
• Popular green romaine varieties are Romulus, Green Forest and Coastal Star. In the red romaine series, Breen and Rouge D’Hiver are standard. Also try Winter Density with its smaller frame and good flavor and texture.
• Popular green leaf lettuce types are Bergam’s Green and Green Star. New Red Fire is the standard large-frame red-leaf lettuce. Lolla Rossa is popular for a small-frame, red-leaf lettuce.
• Popular bibb types are Buttercrunch and Little Gem.
• Popular green Boston types are Nancy and Adriana, and Skyphos is a standard red Boston.
• Choosing the right Salanova type depends on its use and market. Most people grow it as a head to be cut as a salad mix. Some growers plant this on black plastic mulch and harvest 3 cuttings, as opposed to removing the head and removing the stem at the wash and pack station. 

Greenhouse guidelines

• EZ Seeder seeding plate #9

Cell pack tray	Germination temp	Growth temp	Hardening off	Notes
72, 98 or 128	Below 80°	60°–75	Withhold water	Sow 1 seed per cell. Put plug trays on a wire mesh bench to encourage air pruning.

Number of successions

• Start planting lettuce in the greenhouse 4 weeks before you expect to start transplanting in the field. Follow with a second planting 12 days later. Reduce each following succession by 1 day until plantings are weekly. In other words, the intervals between plantings will be 12-11-10-9-8-7-7-7, etc. This succession rate will reduce the incidence of several plantings coming in at the same time. Of course, the weather plays a large role in this as well. 
• Continue seeding lettuce weekly until the growing season is over. In the northern United States we stop seeding lettuce in the greenhouse around the third week in August for the November harvest. Increase the number of plants during August if your markets demand a regular supply.

Seeding tips

• If the weather is too hot, keep flats in a cool location until seeds germinate.

Transplant readiness indicators

• Plants should easily come out of their cells. Plants should generally not be older than 3–4 weeks.
• Remove from the greenhouse 5 days before planting.

Transplanting in 5- or 6- foot raised beds

Rows	In-row spacing	Planting depth (inches)	Notes
3 to 5	6-12 inches	Do not bury plants. Leave the top of the root ball a little aboveground to avoid bottom rot.	Adjust the spacing based on the variety (see below).

• Romaine types: 12 inches in-row with a row distance of 15–18 inches
• Butterhead types 12 inches in-row with a row distance of 12–15 inches
• Greenleaf and red-leaf types: 10 inches in-row with a row distance of 15–18 inches
• Salanova types: 6 inches in-row with a row distance of 10–12 inches

Water wheel transplanter

Rows	In-row spacing	Planting depth (inches)	Notes
2-3	6-12 inches	The top of the root ball should be above the soil line to avoid bottom rot.	Add kelp to water as a 0.5% solution in the water wheel planter.

Cultivation procedures (without plasticulture)

• Prepare the seedbed 1–2 weeks in advance, and shallowly stale seedbed before planting to eradicate weeds if possible. Don’t disturb the soil too deeply as new weed seeds will be brought up.
• Use a basket weeder or wheel hoe when weeds are in the white thread stage, without burying the young crop. Weed control is more effective when you eliminate weeds before they emerge. 
• Hand hoe or hand weed between plants.

Cultivation procedures (with plasticulture)

• Cover plants with a floating row cover and support it with 10-gauge wire to support the row cover, since abrasion against the cover will damage the plants.
• Cultivate with a rolling cultivator or Spyder to control weeds in between the plastic.
• If weeds between the rows are an issue, cover the areas with weed fabric as opposed to mulch, to avoid slug damage.

Deer, frost, disease and insect protection

• To prevent deer damage, build a temporary fence using 4-foot fiberglass posts and attach 1 clearly visible wire like IntelliTape at about knee height. Build a second fence inside the first fence, but attach 2 wires or twine whereby the top line is about 7-feet tall. Deer don’t have very good depth perception and won’t attempt to jump this fence without checking out the first fence, so electrifying the second fence is often not needed. Bait the outside deer fence with peanut butter and electrify it. Make sure you build the fences, bait and electrify on the same day. The surprise effect is what matters most with this particular deer control.
• To prevent bottom rot (Rhizoctonia) and grey mold (Botrytis), provide drainage, avoid excessive overhead irrigation, control weeds and plant transplants ¼ inch above the soil surface.
• To prevent downy mildew (Bremia lactucae), use resistant varieties.
• To prevent viruses, use certified-disease-free seed, and reduce cross contamination by controlling whiteflies and aphids.
• You can prevent cutworms by spraying the soil with the beneficial nematode Steinernema carpocapsae. Once the pest is in the crop, control the population by spraying the crop with Bacillus thuringiensis kurstaki, or spread a baited product containing spinosyn, like Seduce, around the plants.
• Watch for aphids and whiteflies; place yellow sticky cards at plant height and check them at least twice a week. Control them with Beauveria bassiana, as in the product Mycotrol ESO. Repeat every 5–7 days. You’ll see results a week after applying. Act when pest pressure is still low. Alternatively, you can use insecticidal soap (just against aphids), but when an infestation is heavy, use a pyrethrum-based product, such as PyGanic EC 5.0 II. This product requires a neutral pH to dissolve. Pyrethrum breaks down quickly when exposed to UV light (it has a half-life of 12 hours) and is considered among the shortest-acting insecticides. It’s also toxic to bees and other pollinators. For both reasons, apply a pyrethrum-based product in the evening. 

Other cultural practices

• Irrigate frequently for optimum yield and plant health. Frequency depends on soil type, evaporation, precipitation and the particular needs of the crop. 

Cover cropping and/or double cropping

• Lettuce is suitable for double cropping. As lettuce creates little crop residue, plant direct-seeded crops like arugula and spinach after it.
• Work under any harvest remains to avoid insect or pathogen buildup, and plant a cover crop. In the northern United States and Canada, you can follow summer- and early-fall-harvested lettuce with a cover crop of oats and peas in September, or rye and vetch planted at later dates. Adjust accordingly in other regions.

Additional resources

• Organic Production and IPM Guide for Lettuce

Production, Direct-Seeded Salad Mix

---

Soil preparation

• Jang, Sutton Jr. or Planet Jr. planters in combination with small seeds like lettuce don’t perform well with plant matter on the soil surface, so avoid planting them after tall green manures.
• Create a fine and firm seedbed when direct seeding lettuce. Prepare the seedbed a few weeks before planting to encourage weeds to germinate. This provides the opportunity for some initial weed control via shallow cultivation or flaming.
• Alternatively, place a silage tarp over the prepared and irrigated seedbed 3–5 weeks in advance of the seeding date, depending on the time of year. This will flush many annual weed seeds and reduce weed pressure. Remove the tarp when the weeds have died. 

Varieties

• When downy mildew is an issue, only select resistant varieties. Favorites among growers are Salanova, Red Salad Bowl, Outredgeous, Green Salad Bowl and Defender. While Salanova is popular as a salad green, it’s cost prohibitive for direct seeding. For growing this type, see the Lettuce, Main Crop section.

Direct seeding information

Seeder	Rows	Seeds per foot	Seed plate no.	Depth (inches)	Sprocket setting	Notes
Planet Jr.	5	60	7	2
Sutton Jr.	10-20	25-50	7-8	1/4-1/2		Go at 1 mph. Reduce the seeding rate (by driving faster) when planting 17 rows to maintain a population of 20–40 seeds per square foot.
Jang	5	24	X24 or XY24		Front 14/rear 9 or 10

Number of successions

• Start seeding salad mix as soon as you’ve prepared the ground in the spring. Follow with a second planting 12 days later. Reduce each following succession by 1 day until plantings are weekly. In other words, the intervals between plantings will be 12-11-10-9-8-7-7-7, etc. This succession rate will reduce the likelihood of several plantings coming in at the same time. Of course, the weather plays a large role in this as well. 
• Continue seeding salad mix on a weekly basis until you run out of growing season. In the northern United States, we stop seeding salad mix around the first week of September for the November harvest. Increase the number of beds during the month of August if your markets demand a regular supply. Continue to seed salad mix in a high tunnel for season extension.

Cultivation procedures

• Use a basket weeder or wheel hoe when weeds are in the white thread stage, without burying the young crop. Weed control is more effective when you eliminate weeds before they emerge. Mechanical weed control becomes very challenging when planting 17 rows. 
• Hand weed in between plants but make sure you don’t pull up any soil. A 17-row salad mix has the advantage that the leaves are prevented from falling horizontally and so tends to be cleaner than planting it in 9 rows. 

Cover cropping and/or double cropping

• You can plant another short-season vegetable crop like spinach, radish or arugula after an early-harvested salad mix. Mow plants as low as possible with a flail mower. Incorporate crop residue.
• For later dates, work under any harvest remains to avoid insect or pathogen buildup, and plant a cover crop. In the northern United States and Canada, you can follow summer- and early-fall-harvested salad mix with a cover crop of oats and peas in September, or rye and vetch planted at later dates. Adjust accordingly in other regions.

Harvest, Full Size

---

Yield	An average of 1 marketable head per row foot when planted at 10 inches. Numbers are higher for compact varieties that are planted at higher populations (like Salanova). Yields drop down under heavy pressure from thrips or white flies that cause viral infections during August unless you implement a good spraying program.
Standards	Harvesting1 Approximately 100–150 heads of lettuce per person, per hour for cutting, with a second person packing the lettuce in boxes at a rate of 300 heads per hour, when packing 16–24 heads into 1 ¾-bushel boxes
	Washing 150–240 heads per person, per hour
Tools and supplies needed	Knives and 1 ¾-bushel plastic boxes
1Harvest rates don't include the time required to transport crops from the field to a wash and pack shed or storage facility.

Ready-to-harvest and quality indicators 

• Heads are firm, weighing anywhere from 0.8 lb. (Boston lettuce) to 1 lb. (green leaf or romaine).
• Lettuce doesn’t have the beginning of a seed head (it hasn’t started to bolt). The growing point of the lettuce has not elevated from the basal plate.

Harvest procedures

• Harvest in the morning to avoid field heat accumulation.
• Use different boxes in the field from the ones you use for distribution.
• Wash hands and sanitize knives before harvesting.
• Determining the correct cutting height is important and can save time. Cut high enough to remove dead and damaged outer leaves while keeping most of the head intact.
  • Cleaning after cutting is unnecessary when heads are cut with skill. 
  • One suggestion is to stay close to the place where you’ll make the cut by working on your knees. This way you can easily bend over to see where the knife is entering the plant.
• Lettuce should not touch the ground after you cut it. To avoid this, do your cutting and packing in the same motion.
• Pack lettuce so the bottom of the plant doesn’t touch any leafy parts. Lettuce releases a milky juice where it has been cut, and this can leave a brown stain on the leaves.
• For Boston lettuce, pack one layer face up and the other face down. For green, red and romaine lettuces, pack all the heads in one direction.

Washing and racking procedures

• Wash hands and rinse boots before entering the wash-and-pack shed, and cover up field clothes with a bib. If a long-sleeve shirt contains soil, remove this as well.
• If heads are clean in the field, you only need to rinse the bottom of the lettuce to remove the milky juice. Leaving this on will make the bottom turn brown and the head will appear old. Repack in clean boxes and put directly into a cooler.
• If lettuce is dirty, dump heads into the washing tub. Clean tubs thoroughly and add a sanitizer to wash water. Use the guide How to Wash Produce Using a Peracetic Acid Solution to establish how much hydrogen peroxide and peracetic acid solution to add to water.
• Make sure to remove dirt from the cut ends either with gloves or with a brush. Shake out any excess water or let the heads dry upside down to drain water and sanitizer out of the lettuce head.
• Make sure the lettuce is only underwater for a short amount of time so it doesn’t get waterlogged.
• In the cooler, stack heads of red leaf, green leaf and romaine lettuce upside down to let the water drain. Washing Boston lettuce is problematic because it’s difficult to remove all the water from it, and it will break down prematurely if it remains wet.

Additional Resources

• Wholesale Packing and Grading Instructions Romaine Lettuce
• Production Guide for Storage of Organic Fruits and Vegetables 

Packing and storage summary for full-size lettuce

	Leave dead yellow leaves in the field.
Packing in the field	Harvest in plastic 1 ¾-bushel bins, making sure the cut ends never touch the leaves. Use different boxes for delivery.
Packing for delivery	Boston 10 lbs. in 1 ⅑-bushel boxes, with 12 heads to a box 20 lbs. in lettuce boxes, with 24 heads to a box Loose leaf 22 lbs. in lettuce boxes, with 24 heads to a box 12 lbs. in 1 ⅑-bushel boxes, with 12 heads to a box Romaine 22 lbs. in lettuce boxes, with 24 heads to a box (unless you pack romaine hearts) 12 lbs. in 1 ⅑-bushel boxes with 12 heads to a box (unless you pack romaine hearts) Pack 12 heads in 1 ⅓-bushel boxes for CSA delivery. Make sure the cut end of one head doesn’t touch the leaves of another. See the International Federation for Produce Standards for the correct PLU code. Add the prefix 9 for organic crops.
Storage	At 32° and 98–100% humidity. Pack in closed containers for storage that lasts longer than a few days. Lettuce is sensitive to ethylene exposure, which will turn the ribs of leaves brown or cause them to develop brown spots. Allow for good air exchange and don’t store with crops that release ethylene.

Harvest, Salad Mix

---

Yield	An average of 1 lb. of salad mix per bed foot when planting lettuce at 7–14 rows per bed. When using transplanted Salanovo for salad mix expect a yield of ⅓ lbs per row foot.
Standards	Harvesting1 4–5 boxes per person, per hour when the crop is free of weeds and other issues (at 8 lbs. per box) Machine harvest can be up to 35–50 bins per hour (involving 3 people). The rate greatly depends on crop quality, weed infestation and other field conditions. The machine will need to be slowed down dramatically for sorting when there is a high amount of weeds or yellow leaves.
	Washing 8–12 boxes per person, per hour
Tools and supplies needed	Either a machine harvester, handheld harvester or harvest knives; and plastic 1 ⅓-bushel boxes.
1Harvest rates don't include the time required to transport crops from the field to a wash and pack shed or storage facility.

Ready-to-harvest and quality indicators 

• Leaves are 4–8 inches tall and healthy.
• Plants are free of weeds, yellowing, necrosis or other blemishes

Harvest procedures

• Wash hands and sanitize knives and equipment before harvesting salad mix.
• Harvest in the morning hours to avoid field heat accumulation.
• Use different bins for harvesting from those used for distribution.
• Walk the fields before harvesting to inspect the crop for animal damage or feces. Mark these spots with a flag so the tractor operator or harvest crew can avoid harvesting near them.
• When machine harvested:
  • Weed the field thoroughly before harvesting, otherwise the people on the machine won’t be able to keep up with sorting at the speed of harvesting.
  • During harvesting, remove all yellow leaves off the belt before they fall into the crates. When using a hand-held harvester, you’ll sort after harvesting.
• When hand harvested with a knife:
  • Hold a small bunch of leaves at the top of the plant with one hand and cut with one motion using the other hand.
  • Shake vigorously to remove any yellow leaves or stems from previous cuttings.
  • Place loosely in a box.

Washing and packing procedures

• Wash hands and rinse boots before entering the wash-and-pack shed, and cover up field clothes with a bib. If a long-sleeve shirt contains soil, remove this as well.
• Add a sanitizer to wash water. Use the guide How to Wash Produce Using a Peracetic Acid Solution to establish how much hydrogen peroxide and peracetic acid solution to add to water.
• When a commercial salad washer isn’t available, wash salad mix at least twice, preferably 3 times. Using a bubbler to agitate the water reduces damage to the leaves. You can use hydrocooled water for the last rinse.
• Don't leave greens in water for longer than 1 minute. The leaves tend to get waterlogged after a few minutes, which causes them to deteriorate faster.
• Dry salad mix with a centrifuge. There are different sizes and models of commercial-grade salad spinners available through restaurant equipment suppliers. 
• Pack in sealed, ½-bushel boxes, or line the boxes with a plastic liner to avoid having the product lose moisture.

Additional resources

• Production Guide for Storage of Organic Fruits and Vegetables

Packing and storage summary for salad mix lettuce

Cleaning in the field	Inspect the crop for weeds, yellow leaves and contamination.
Packing in the field	8 lbs. per regular bushel box
Packing for delivery	3 lbs. per regular ½-bushel box See the International Federation for Produce Standards for the correct PLU code. Add the prefix 9 for organic crops.
Storage	At 32° and 98–100% humidity. Pack in plastic bags inside closed containers for longer storage. Salad mix is sensitive to ethylene exposure, which will turn the ribs of leaves brown or cause them to develop brown spots. Allow for good air exchange and don’t store with crops that release ethylene.

This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture through the Sustainable Agriculture Research and Education (SARE) program. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.