Updated: Mar 24, 2022
Not all seeds benefit from being started indoors. Some vegetable seeds do better planted directly into your garden and do not hold up well to being transplanted. Other vegetables grow so quickly that it is not worth the space or effort to start the seeds indoors. Most flower seeds, on the other hand, take longer to grow and benefit from the head start of being seeded indoors in the weeks prior to your last spring frost.
Here is a list of what seeds to start indoors and what to direct sow outdoors in growing zones 2 - 4 of Canada or other similar cool gardening climates.
Vegetable Seeds to Start Indoors
These vegetable seeds have longer days to maturity (find this information on your seed package) and benefit from being started indoors or being purchased from a gardening center already started. If you wish to start your own seeds check out When To Start Seeds Indoors for a printable guide with suggested seeding dates for these vegetables along with common flowers.
Asparagus (perennial plant that takes 3 years until first harvest)
Cucumbers (can be started indoor or out)
Onions (if growing from seeds not bulbs)
Squash (can be started indoors or out)
Most herbs (besides dill) benefit from being started indoors. Peppermint is a perennial and will come back year after year. Take note, peppermint can be invasive in you are not careful to keep it in check.
Vegetable Seeds to Direct Sow
Plant these vegetable seeds directly into your garden. There is no need to start these quick growing seeds indoors. Root vegetables (ie. carrots, beets, potatoes) do not like to be transplanted and you will stunt their growth and actually harm them if you attempt to transplant your root crops. To find out when to plant these vegetable seeds in your garden in zone 3 Alberta read When to Plant Your Garden.