Seed Starting

For Toronto area gardeners, starting seeds indoors is crucial for getting a head start on the growing season! This mini-guide outlines the essential steps and materials for successfully growing your own healthy vegetable transplants.

Essential Materials for Indoor Seed Starting

Prepare for your season of vegetable gardening by gathering the following items. A clean start is key to preventing disease.

  • Clean Containers and Tools: Always clean all previously-used trays, pots, and tools before use to reduce the risk of bacteria and fungus.
  • Growing Media: Ideally, use a sterile, soilless seed-starting mix (peat moss, perlite, etc.). Note that a potting mix can also be used but then be careful not to overwater the soil.
  • Containers: Use appropriate tray inserts or pots. If you want to avoid extra work later, choose larger cells to minimize the need to “pot up” before transplanting.
  • Light: Grow lights (full-spectrum is recommended) and a timer are vital, as even a south-facing window may not provide enough light energy for optimal growth – plus overhead lights are better than side windows which can cause slanted growth.
  • Heat: A horticultural (waterproof) heating pad is highly recommended for optimal seed germination.
  • Moisture Management: A layer of vermiculite or a humidity dome helps maintain consistent dampness.
  • Airflow: A small fan is ideal for air circulation to strengthen stems and prevent disease.
  • Watering: A watering can with a sprayer.
  • Seeds: Of course!

Step-by-Step Seed Starting

Successful seed starting depends on managing heat, moisture, and light precisely.

  1. Prepare the Mix: Use room temperature water to dampen your soilless mix in a bucket. The mix should be moist enough to form a “snowball” but not sopping wet. This moisture level is critical for preventing damping off, a common fungal issue. As an alternative, you can pour the seed starting mix directly into the seedling trays but add water in several small increments to ensure the mix is completely damp but not sopping wet. 
  2. Plant and Tamp: Fill your trays with the prepared mix and tamp the soil lightly. Plant seeds at a depth of two to four times the seed’s width. For a higher germination rate, plant two seeds per cell. Lightly tamp the soil surface again to ensure good seed-to-soil contact and remove any large air pockets.
  3. Create a Warm, Damp Environment: Cover the seeds with a thin layer of vermiculite or a humidity dome to retain moisture. Place trays in a warm area. If the veggies are “hot crops” then aim for a consistent 25°C soil temperature for fast germination. If the veggies are “cool crops” then room temperature is ideal.
  4. Introduce Light and Airflow: Once most seeds have germinated and their leaves have emerged, immediately move the trays under grow lights and activate a fan for adequate ventilation. Schedule the lights to run for 12-16 hours per day. If using a dome, remove it once seedlings are about 1+ inches (3 cm) high.
  5. Manage Water and Temperature: Once germinated, the soil should be kept moist but be allowed to dry slightly between waterings. This is necessary to ensure the roots can access the oxygen they need. Aim for day temperatures of 21-25°C and night temperatures of 12-18°C to stimulate strong growth.

Caring for Seedlings and Planning Your Harvest

As your seedlings grow, they require attention to ensure they are robust enough to handle the transition to the outdoors.

  • Thinning: If you planted two seeds per cell, you must thin them to allow the strongest plant to thrive. Cut the stem of the thinner-stemmed (or less straight-stemmed) seedling at the soil level; do not pull it out, as this can injure the remaining seedling’s delicate root system.
  • Fertilization: For optimal growth and thick, healthy stems, begin adding a balanced, diluted fertilizer lightly every one to two weeks, starting after three weeks of growth. Reduce fertilizer if the seedlings become overly large or “leggy.”
  • Succession Planting: For crops where you harvest the entire plant at once (determinate types like cabbage), stagger your planting by starting seeds in batches two weeks apart. This approach, known as Succession Planting, ensures a continued harvest throughout the season instead of a single, overwhelming yield.
  • Potting Up: If your seedlings outgrow their containers before outdoor planting, transplant them into a larger container to ensure continued healthy growth. This is a common requirement for plants started early.
  • Hardening Off: Seedlings are tender! They must be slowly acclimatized to outdoor conditions (sun, wind, temperature swings) in the 6–10 days leading up to their final outdoor transplant date.

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.
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