Learn to Grow Seeds Indoors!

Welcome to Learn to Grow Seeds Indoors! This information was developed and presented in workshop format by Bridget Indelicato, Founder, Innisfil Seed Library (2017).

Quick Links:

Test your seeds for viability

Seed planting dates

Equipment & supplies

Companion planting

seedling 6

You'll learn how to:

  • Determine which and when different seeds need to be started in our zone (5a for Innisfil, ON)
  • Plant your seeds indoors from beginning to end
  • Create your own seed starting system that can be used year after year
  • Care for your sprouting seedlings and plants
  • Prepare your seedlings for the great outdoors
  • Plan beneficial pairings in the garden using “companion planting”

What should I start indoors?

Some plants have a long growing period before maturity so starting them indoors ahead of planting in your garden will ensure that your plants are maturing when they should. Some common plants to begin indoors are tomato, tomatillo, sweet and hot peppers, eggplant, brussel sprouts, cabbage, broccoli, cauliflower, cucumber, corn, okra, pumpkin, squash, herbs, and flowers. While some of these plants may be started indoors, most grow quickly and benefit from being directly sown in your gardens: radish, carrot, spinach, beans, beets, leafy greens, onion sets, peas, arugula, bok choy, turnip, and swiss chard. With older seeds in your collection, it's strongly recommended that you test your seeds for viability at least a week before you begin planting so that you increase your chances of success and don't waste time waiting for seeds that won't germinate.

When do I start seeds indoors?

You need to determine last frost date in your region, the growth period specific seeds need and the safe set out date for planting the seedlings in your garden.

  • In Innisfil/Barrie area, we are zone 5a with a last frost date of May 20 (ref. Veseys Canada)
  • Calculate your safe set out/planting date by adding or subtracting the number of weeks from the last frost date
  • For example, tomatoes requirement 6 to 8 weeks to grow into a strong seedling and should be planted outdoors one week after the last frost date (frost kills!). Working with the date of May 20 as the last frost date in our region, calculations determine starting your seeds indoors 8 weeks prior on March 25, and planting them outside on May 27, one week after danger of frost.
  • Based on our region with zone 5a, here are a list of common seed planting dates.

Let's get started!

Step 1: Create your seed starting system

seed starting system

1. Pick a location in your home that is well-ventilated, preferably warm, and a committed space for a few weeks.

2. Get your equipment and supplies, including recycled materials.

3. Lights should be dropped close to the tops of your cells/pots. Use a cool and warm bulb in each unit to help mimic natural light. 

4. Set your timer set for 12 to 16 hours. Take advantage of lower electricity rates by programming your lights overnight, and draw your curtains during the day.

Step 2: Plant your seeds in seed starting mix


1. Using an organic seed starting mix, plant 2-4 seeds in each cell/pot to increase chances of germinating seeds. Label each cell.

2. Lined trays will keep your  shelves dry and allow your seedlings to wick pooling water. We recommend lining your trays with kitchen garbage bags.

3. Some seeds can benefit from heating mats to help with germination.

4. Keep the seeding mix moist but not soggy.

5. Watch for sprouts! Check for typical germination time periods for specific seeds. Wait to see the first leaves called “cotyledons.”

Step 3: Transplant your seedlings into bigger pots with potting soil


1. Generally when the first two “true leaves” (leaves appearing after the cotyledons) appear it’s time to transplant and up size to a 4-inch pots filled with potting mix. Potting mix provides more food for the growing plant.

2. Larger pots allow more room for roots to branch out, creating a strong healthy foundation for your growing seedling.

3. Reuse clean 4-inch pots, coffee cups or larger yogurt/butter/sour cream containers (be sure to make holes for drainage).

Step 4: Care for your indoor seedlings


1. As seedlings grow in height, adjust the height of the lights by moving the lights or the adjustable shelves.

2. Keep potting soil moist but not soggy.

3. If possible, provide airflow with an oscillating fan to strengthen stems and prepare them for wind in the outdoors.

4. As seedlings grow taller, you may need to stake them for support.

Step 5: Harden off” your seedlings


1. It's time to start introduce your seedlings to the outside world!

2. When weather conditions become warmer and the outdoor planting date is approaching, begin to take your plants outside for short period of time.

3. Begin in a sheltered location in the shade for a few hours a day. You don't want to stress your seedlings with direct sunlight or strong winds during this initial exposure to the outdoors.

4. Bring your seedlings indoors at night as temperatures drop (putting them in garage or shed okay if overnight temperatures are fair).

5. Get bolder! After a couple of days, start to place your plants in dappled sun and unsheltered spaces where they can experience gentle breezes.

6. Over time, introduce them to full sun, further out in your yard and away from protection.

7. Be sure to use stakes for plants that need support to avoid breakage of stems.

8. Wilting may happen from sun and wind; move into shade and back into sun once they perk up again.

9. In time, keep them outside overnight.

10. Be sure to keep them well watered

Step 6: Outdoor transplanting of your seedlings into your garden!


After all your care and attention it's time to transplant your plants into the garden. If possible choose an earlier time of day when the garden is in shade or in dappled light. This will help with the shock of transplanting. Water well.

Consider companion planting when your choosing the location of your seedlings and direct sow seeds. Companion planting is consider what you plant next to each other in the garden as some plants will benefit others and some grow poorly together. Benefits may include enhanced flavour of vegetables and warding off unwanted bugs. Non-benefits usually means stunted growth. 

Have questions? Get in touch!