Starting Onions from Seed Indoors

Farm and Garden, Penn State Extension, Franklin County
181 Franklin Farm Lane, Chambersburg, PA 17202
Telephone: 717-263-9226
http://extension.psu.edu/franklin

Starting Onions from Seed Indoors

Onions are one of the first plants to be seeded for transplanting because they take a significant amount of time (6 to 8 weeks) to reach transplant size and because they can be set out relatively early (late March here in Franklin County). Therefore, it’s best to start onion seeds in mid- to late-January. Onion seed should be placed ½ to 3/4 of an inch apart in a pot or flat filled with a sterile, seed starting mix. Place the container in a warm (75 to 80 F) location until young seedlings emerge. Move to a cooler location (60 to 65 F) when the seedlings are 1 to 2 inches tall.
    

Make sure they have plenty of light, using florescent lights as needed.

    

Start fertilizing when the seedlings reach 2 to 3 inches tall, using a soluble fertilizer with each or every other watering.

  

Encourage stockiness by trimming the ends of the leaves when the plants reach 4 to 5 inches tall. Harden off the onions in early March by moving the plants to a protected outdoor location. You may have to move them inside temporarily to protect them from extreme cold snaps.

  

Onion seeds do not store well, so purchase seeds annually for best results.