Lettuce Growing Tips

 

Our first outdoor lettuce bed in May.
Photo Wren Vile

 Lettuce growing conditions – germination

  • Lettuce seed needs light to germinate – don’t sow too deep: 1/4″–1/2″ (6–10 mm) is ideal.
  • Minimum soil temperature for germination is 35°F (1.6°C).
  • Optimum temperature range for germination is 68°F–80°F (20°C–27°C). I have a table of optimum soil temperatures for germination in my book The Year-Round Hoophouse
  • Germination takes 15 days at 41°F (5°C), 7 days at 50°F (10°C), 3 at 68°F (20°C), only 2 days at 77°F (25°C)
  • Germination takes 3 days at 86°F (30°C), but will not occur reliably at temperatures hotter than that.
  • A soil thermometer soon pays for itself and saves lost crops and frustration.

Lettuce crop requirements

  • Free-draining soil, high organic matter, pH 6.0–7.0.
  • Fertile soil with good tilth will help roots grow.
  • Don’t overdo the nitrogen – encourages E. coli.
  • Keep lettuce growing quickly for good flavor – plenty of water throughout its growth.
  • Ideal growing temperatures 60°F–65°F (15°C–18°C).
  • Some growth whenever the temperature tops 40°F (4.5°C).
  • Cultivate regularly and shallowly to remove weeds.
Lettuce nursery bed with soil thermometer behind the sheep
Photo by Bridget Aleshire

Sowing lettuce for transplanting

  • You can sow in cell-packs or plug flats, 3 seeds per 1″–2″ (2.5–6 cm) cell, later reducing to 1 seedling with scissors.
  • If suitable germination space is limited, sow seed in a small flat or shallow pot, then spot the tiny seedlings into bigger flats or 606-cell packs (2″ × 2″, 5 × 5.6 cm) to grow on before planting out.
  • Can use an outdoor nursery bed from mid-April to October, rather than flats. Transplant the bare-root plants directly from the seedbed.
  • But in very hot weather, indoor sowings might give more reliable germination.

Transplanting lettuce

  • Harden off before transplanting.
  • Transplant lettuce seedlings at 4–6 true leaves, 3–6 weeks of age depending on how fast they are growing.
  • Handle transplants only by their leaves or the root ball—try not to touch the roots or stem. This minimizes the damage from your hands.
  • 8″–12″ (20–30 cm) spacing for full-sized heads. Close spacing lets foliage cover the bed completely, creating a cooler microclimate.

Lettuce Types

  1. Iceberg (crisphead) lettuces have little nutritional value. They have no frost tolerance because of their high water content. 75-100 days from direct seeding.

    Buttercrunch Bibb lettuce. Photo Kathleen Slattery
  2. Butterheads (bibbs) have very tender leaves, but have shorter shelf-life than romaines and leaf varieties. 60-75 days from direct seeding.
  3. Romaine (cos) lettuces are upright, often very crisp and flavorful. They have more vitamins than other lettuce types. &0 days or more from direct seeding.

    Green Forest romaine lettuce.
    Photo Pam Dawling
  4. Leaf lettuces include the familiar oak-leaf types, and frilly ones. You can harvest individual outer leaves or cut the whole plant. 45-60 days from direct seeding.
  5. Batavian lettuces (summer crisp or French crisp) are tasty, thick-leafed varieties that have great heat and cold tolerance. Although sometimes classified with icebergs as crisphead types, they are very different.
  6. Multileaf lettuces – familiar Tango, Panisse and Oscarde, and the newer Salanova, Multileaf and Eazyleaf brands. They are bred for uniformly small leaves, with more texture, loft and flavor than baby mixes and faster harvesting. Transplanted 6″–8″ (15-20 cm) apart they produce 40% more than baby leaf mixes. The full-size plant can be harvested as a head, providing a collection of bite-sized leaves. Or just one side (or the outer leaves) of the plant can be cut and the plant will regrow for future harvests. Growing multileaf heads takes 55 days, compared to 30 days for baby lettuce. For the most harvest, pick the outer leaves and let the middle regrow.

    Ezrilla Tango-type one-cut multileaf type lettuce
    Photo High Mowing Seeds
  7. Baby lettuce mix, aka mesclun, salad mix, spring mix and misticanza. Some mixes include other greens. 21 days from seeding in mild weather. Up to 63 days in cold weather.

Lettuce varieties for every time of year

We used to reckon on five lettuce seasons, but with climate change, our Early Spring shrank and became encompassed in our Spring, so now we have 4 lettuce seasons, and we always sow 4 diverse varieties:

  • Spring (Jan 17 – April 22), 8 sowings. Priorities: fast growth, cold tolerance
  • Summer (April 23 – Aug 14), 20 sowings (lots of seed!). Priority: extreme heat tolerance/bolt-resistance. I just sowed our first batch of summer varieties on April 23
  • Fall (Aug 15 – Sept 7), 9 sowings. Priorities: some warmth-tolerance, some cold tolerance
  • Winter (Sept 8 – 24), 9 sowings. Priority: cold-tolerance

Season extension techniques for lettuce in spring

  • Fast-maturing hardy varieties
  • In early spring, use transplants for earlier harvests
  • Warm microclimates (protection from prevailing winds)
  • In spring, warm the soil with black plastic mulch
  • Use rowcover
  • Harvesting early in the year might mean fast production in January and February, or it might mean starting in the fall and overwintering the plants. See my post series Lettuce of the Month, for ideas on varieties and techniques throughout the year. See here for the overview.
A stormy early spring day, garlic, rowcovered beds and our hoophouse.
Photo Wren Vile

Avoid lettuce bolting

Assess your risks and if in doubt, harvest early. Bolting and/or bitterness are more likely with

  • Under-watering,
  • Long days,
  • Mature plants,
  • Poor soil,
  • Crowding,
  • High temperatures,
  • Bolt-resistance generally goes from Leaf types (first to bolt), through Romaines, Butterheads, Bibbs, to Crispheads.
  • Vernalization—once the stems are thicker than 1/4″ (6 mm), if plants suffer 2 weeks of temperatures below 50°F (10°C), followed by a rapid warm-up.
  • Also see What makes vegetable crops bolt and how can I stop it?
You don’t want this! Bolting lettuce outdoors in July
Photo Alexis Yamashita

Keys to year-round lettuce success 

  • Store seed in a cool, dry, dark, mouse proof place.
  • Good soil preparation and high organic matter are important for high quality lettuce, which needs to grow quickly.
  • Location, location, location! We grow lettuce outside from transplants from February to December (harvesting from late April); in a solar-heated greenhouse from September to March (harvesting leaves from November) and in a solar heated hoophouse from October to April (harvesting leaves from November, and whole heads in April). We also sow baby lettuce mix in the hoophouse from October to February, for harvest multiple times from December to April.
  • Use shade cloth on hoops in hot weather
  • Use rowcover in cold weather, or plant in cold frames, greenhouses or hoophouses.

Scheduling lettuce for continuous harvests

  • Lettuce grows faster at some times of year than others, and the time between one sowing and the next needs to vary to balance this.
  • To harvest a new planting every week you need to have sowing gaps of more than 7 days in the spring, 6-7 days in the summer, less in fall.
  • In warm spring weather, baby heads of lettuce or individual leaves can be ready to harvest 4 weeks after transplanting, and full-sized heads 6 weeks after transplanting.
  • In summer, full-size heads can be ready in as little as 3 weeks from transplanting.
  • As temperatures and day-length decrease in the fall, the time to maturity lengthens, and a single day’s difference in sowing date can lead to almost a week’s difference in harvest date.
  • Lettuce for harvest in February will take 2-3 times as long from planting to harvest as that for September harvest.
  • December and January sowings grow very slowly, and early February sowings will almost catch up.
Flats of lettuce transplants in our cold frame in April.
Photo Pam Dawling

Scheduling lettuce January-June

January: sow every 2 weeks

  • Sow indoors in flats in late January for outdoor transplants
  • If you have a greenhouse or hoophouse, transplant there until mid-February
  • Harvest leaf lettuce and baby lettuce mix from protected crops

February: sow every 2 weeks

  • Same as January

March: sow every 13 days, indoors in flats

  • From late March or early April, you could switch to outdoor direct sowing. (We transplant all our lettuce.)
  • Transplant the first 3 sowings outdoors with rowcover
  • Harvest leaf lettuce, baby lettuce mix from a hoophouse; starting late March, harvest leaves from the first outdoor planting

April: Sow every 9 days

  • Transplant the March sowings
  • Harvest whole heads from late April

May: Sow every 8 days

  • Transplant 1 week’s needs each week
  • Harvest outdoor heads

June: Sow every 6 or 5 days, under shadecloth

  • Transplant one week’s needs every 6 days, using shadecloth for the first 2 weeks
  • Harvest outdoor heads

See my post Lettuce All Year in a Changing Climate, which includes links to my slideshow about growing lettuce year round, and our Lettuce Varieties list and Lettuce Log (planting schedule). It also includes keys to succeeding with year-round lettuce (dates for succession planting).

Lettuce bed in May.
Photo Wren Vile

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