When to Plant Lettuce in Ontario 2026: Dates by City

🌿 Loose Leaf

• Ready in 30–45 days
• Harvest cut-and-come-again for 3–4 weeks
• Bolts faster in heat than head types
• Best for continuous fresh salad
• Ideal for succession sowing

Best varieties: Black Seeded Simpson, Red Sails, Salad Bowl, Simpson Elite

🥦 Butter Head

• Ready in 55–65 days
• Loose, soft-leafed head — whole harvest
• More heat-tolerant than loose leaf
• Best flavour of all lettuce types
• Buttercrunch is the Ontario standard

Best varieties: Buttercrunch, Tom Thumb, Merveille des Quatre Saisons

🥃 Romaine / Cos

• Ready in 70–80 days
• Most heat-tolerant lettuce type
• Upright growth, crisp texture
• Best for extending into June in Ontario
• Needs the full spring season to mature

Best varieties: Jericho, Paris Island Cos, Forellenschluss

🥘 Batavian / Crisp

• Ready in 55–65 days
• Most bolt-resistant type for Ontario
• Crisp texture, slightly sweet
• Nevada is the best summer performer
• Best choice for late May sowings

Best varieties: Nevada, Magenta, Sierra

Slugs & snails (the #1 Ontario lettuce pest)

Holes in young lettuce overnight; silvery slime trails; worst in damp May/June and after rainfall. Control: iron-phosphate slug bait (Sluggo, Safer's; pet-safe and organic-certified) sprinkled around plants; beer traps sunk to soil level; copper tape around raised beds; hand-pick at night with a flashlight (slugs are nocturnal). Eliminate hiding spots: lift any boards, pots, debris where slugs shelter during the day. Mulch only AFTER plants are established (mulch creates ideal slug habitat for tender seedlings).

Aphids (green peach aphid, lettuce aphid)

Clusters of small green/yellow insects on leaf undersides and growing tips; sticky honeydew on leaves; stunted growth. Most common late spring through summer. Control: blast with cold water from a hose to dislodge (effective and free); introduce ladybugs (sold at Lee Valley); spray insecticidal soap (Safer's) for heavy infestations; row cover prevents winged aphids from landing. Lettuce aphid is the worst — it gets inside heading lettuces and is impossible to wash off; harvest before heading begins if aphid pressure is high.

Leafminer flies

Distinctive white squiggly tunnels through leaves caused by larvae burrowing between leaf surfaces. Worst in May/June. Control: floating row cover (Reemay or Agribon) at transplant time prevents adult flies from laying eggs; remove and destroy affected leaves; rotate lettuce to a new bed each year. Damage is cosmetic on mature plants but ruins baby leaf and salad mix harvests.

Downy mildew (fungal) — humid Ontario springs

Yellow patches on upper leaf surfaces with fuzzy grey/white growth underneath; spreads fast in cool wet conditions. Worst on overwintering lettuce and dense spring plantings. Control: wide spacing for air circulation (30 cm between plants minimum); water at ground level not overhead; rotate to a new bed; resistant varieties (Buttercrunch, Salad Bowl, Sierra, Nevada are reasonably resistant). Remove infected plants immediately — downy mildew spreads explosively in wet weather.

Tipburn (calcium deficiency, not a pest)

Brown crispy edges on inner leaves of heading lettuce (romaine, butterhead). Caused by inconsistent watering, not actual calcium shortage in soil. Control: consistent moisture — lettuce needs 2–3 cm of water per week, never letting the soil dry out. Drip irrigation or soaker hose far better than overhead watering. Mulch (after plants establish) holds soil moisture even. Pick affected outer leaves before the rot spreads into the heart.

Harvest loose leaf cut-and-come-again — don't pull the whole plant

Harvest loose leaf lettuce by cutting outer leaves to 2–3 cm above the base, leaving the inner growing point intact. The plant regrows from the centre and produces 2–3 more harvests over the following 3–4 weeks. This single technique triples the productive life of each plant compared to harvesting the whole head at once. Cut in the morning when leaves are crisp. Once a central flower stalk appears, the plant is done — harvest everything immediately as leaves become bitter within days of bolting.

Afternoon shade delays bolting in late spring

Planting lettuce in a spot that receives afternoon shade — from a fence, taller plants, or shade cloth — reduces heat stress and delays bolting by 1–2 weeks. In Ontario, planting lettuce on the east side of tall crops or structures gives morning sun and afternoon shade. This is particularly useful for late May sowings. Shade doesn't prevent bolting indefinitely — day length is the primary trigger — but it buys meaningful extra harvest time.

Start indoors in March for the earliest Ontario harvest

Sow lettuce indoors under lights in early to mid-March, 4–6 weeks before transplanting outside. Move seedlings outdoors in a cold frame or under row cover in early April, 2–3 weeks before last frost. This gets you a salad harvest in late April to early May — 3–4 weeks earlier than direct sowing. Lettuce transplants easily and isn't sensitive to root disturbance the way beans and cucumbers are. Use cell trays and transplant when seedlings have 3–4 true leaves.

Thin ruthlessly — crowded lettuce bolts faster

Overcrowded lettuce competes for water and nutrients and bolts faster than well-spaced plants. For full heads: thin to 25–30 cm apart. For cut-and-come-again: thin to 15–20 cm apart. For baby leaf harvest: sow thickly and harvest entire rows at 8–10 cm height without thinning, then resow. The thinnings from full-head plantings make excellent baby salad greens — don't waste them.

Fall lettuce is sweeter — don't skip the August sowing

Many Ontario gardeners skip the fall lettuce crop because they associate August with heat and bolting. But August-sown lettuce germinates in warm soil, grows through September's cooling temperatures, and matures in October when cool nights concentrate sugars in the leaves. Fall lettuce is noticeably sweeter and more flavourful than spring lettuce. Sow in late August, water through any September dry spells, and use a row cover to extend the harvest from October into early November in Toronto and Windsor.

When should I plant lettuce in Ontario?

Spring: 4–6 weeks before last frost when soil reaches 4°C. Toronto and Windsor: late March to early April. Ottawa and Kingston: early to mid-April. Fall: 6–8 weeks before first fall frost — mid-August for Toronto, early August for Ottawa. Use the frost calculator for your city's exact frost dates.

Why is my lettuce bitter in summer?

Bitterness in summer lettuce is caused by bolting — the plant has begun flowering in response to long days and heat. Once bolting starts, leaves become bitter and the plant's energy shifts to seed production. Harvest immediately when you see a central stalk forming. For summer fresh salad, switch to less bitter alternatives: Swiss chard, arugula (which is bitter but pleasantly so), or wait for your fall lettuce sowing in August.

Can I grow lettuce in containers in Ontario?

Yes — lettuce is one of the best container vegetables for Ontario balconies and patios. Use a container at least 15 cm deep and 30 cm wide. Loose leaf varieties like Black Seeded Simpson and Red Sails work better in containers than head types. A container on a shaded north-facing balcony can produce lettuce through June when south-facing spots have already bolted. Move containers to shade during the hottest part of summer. Fall container lettuce on a sheltered balcony often lasts into November.

What's the best lettuce variety for Ontario?

Buttercrunch is Ontario's most popular and reliable lettuce — heat-tolerant for a butter head type, excellent flavour, widely available. For the longest season and best bolt resistance, Nevada (Batavian type) is the most heat-tolerant variety available. For fast cut-and-come-again production, Black Seeded Simpson and Red Sails are hard to beat. For fall: Red Sails and Simpson Elite both produce excellent fall crops.