Growing Guide: Lettuce

Lettuce is a versatile foliage crop, typically grown for salads. While it can survive in the sun, it produces a much better flavor when grown as a cool crop. Because it grows quickly and has low nutrient requirements, it is a perfect candidate for both companion planting and succession planting to maximize your garden’s output.  

Planting

  • Location: Select a spot with eastern or southeastern sun. Lettuce often “bolts” (sends up a flower stalk and becomes bitter) when exposed to intense afternoon sunlight.  
  • Soil Preparation: Add at least 1/2″ of compost or loose organic matter and rake it into the top 3-4″ of soil. Mounding the soil slightly is recommended, as lettuce prefers damp but well-draining conditions.  
  • Timing: You can begin planting as soon as the soil is workable, typically late March in Toronto, as lettuce can withstand light frosts. Seeds will germinate in soil as cold as 4°C, though 10°C is the ideal minimum for faster germination and growth rates.  
  • Summer Planting: If planting during the heat of summer, choose a cool, shady location.  
  • Method: You can direct-seed into the garden or start seeds indoors for later transplanting. Using both methods helps spread out your planting dates and ensures a continuous harvest throughout the season.  
  • Spacing and Depth:
    • Cut-and-come-again lettuce: Space 3-4″ apart.  
    • Head lettuce: Space 8-12″ apart.  
    • Technique: Press seeds into the soil surface rather than burying them in deep holes.  
  • Initial Care: Water immediately after planting and keep the soil consistently damp for the first week to ensure germination.  

Maintenance

  • Sun Protection: During heatwaves, use a shade cloth or place tall plants on the west side of your lettuce to block the late-day sun.  
  • Feeding: Fertilize occasionally with nitrogen-heavy supplements. If you prefer extra-crisp leaves, add calcium supplements like CalMag, lime or gypsum.  
  • Safety Note: Avoid using any type of manure in the soil beneath lettuce to minimize the risk of E. coli contamination, as the edible parts grow so close to the ground.  
  • Watering: If you notice drooping leaves, the plant is likely overheated or underwatered. Misting the leaves with water can help cool the plant during the hottest parts of the day.  
  • Weeding: Keep the area well-weeded so that no unwanted plants are accidentally mixed into your harvest.  

Pests and Diseases

  • Common Pests: Lettuce is often targeted by aphids, rabbits, slugs, and snails.  
  • Prevention: Growing your crop beneath a row cover is an effective way to prevent these critters from nibbling on your greens.  
  • Diseases: Watch for gray mold and powdery mildew. To avoid these, ensure you do not overwater and maintain good airflow.  

Harvesting

Lettuce offers two distinct styles of harvest:

  1. Cut-and-Come-Again (Loose-leaf): When leaves are at least 6″ high, cut them down to 2.5″ above the soil. The remaining base will photosynthesize and regrow for future harvests. You can usually harvest each lettuce plant 3-5 times using this method. See photo on the right, above. 
  2. Head Lettuce: Wait until the heads are full-sized, then cut them at the base of the stem.  

Once a head is completely harvested, you can immediately plant new seeds or seedlings in that space to keep your garden productive. 

💡 Tips for Toronto Gardeners 💡

Because Toronto often experiences a very quick jump from a chilly spring to a hot summer, our “lettuce window” can be short. I recommend planting your first batch in late-March and then switching to heat-tolerant varieties (like ‘Oakleaf’ or ‘Romaine’) for your summer sowings to keep the greens coming without them turning bitter. By September, any lettuce variety will work for a fall harvest. 

Ready to Grow More?

Join our community of gardeners and start growing your own food in the city! From balcony boxes to backyard plots, community gardens, and urban farms, we’re dedicated to helping you succeed in vegetable gardening and urban agriculture.

  • In the Greater Toronto Area (GTA)? Join Our Program at Downsview Park: Enroll in our full-season Grow Veggies program for hands-on learning and a share of the harvest.
  • Get Monthly Tips: Sign up for our monthly Grow With Us newsletter to receive seasonal tips and our gardeners’ to-do lists.
  • Follow Us: Find us on Instagram or Facebook to see what we’re growing at our teaching garden in Toronto.