For best growth of onion seed, you should start 10-12 weeks before planting out in warm weather. They are mildly frost tolerant though too long exposure to cold temps might vernalize onions and cause them to go to flower. Once they go to flower, they’ll no longer bulb up. 

Onion seeds don’t need light to germinate and some say they will germinate best with darkness. They will lose their more quickly than many other seeds so if they are 2 or 3 years old, you may get poorer germination. 

With new seeds, sow on 1-inch centres by lightly raking them with a fork into the soil or poking them in slightly and then watering in. If your seed is older than a year old, you may want to sow a bit more thickly assuming more that germination will be more erratic. Once they are up and growing, you can space more evenly. 

Many people will suggest that you trim onion seedlings when they start to get leggy though I usually do not do this and it doesn’t seem to affect growth. So cutting off the often seedy tops will probably not harm and may help. 

Transplanting alliums is easy as they are monocots (one baby leaf) with unbranched roots. Just gently lift out a bunch and give even spacing on 3 inches square while they are growing in trays.

You’ll want to transplant into the garden about 6 inches apart. You can plant singly or in clumps but if in clumps then use wider spacing. It doesn’t hurt to plant a little deeper than you grew them. This will help anchor young seedlings. You can see in the above picture that I use to trench onion seedlings while plant. So I made a furrow, laid out the seedlings then back filled the furrow. Make sure you keep rows well weeded and/or mulch between them. They will do best with regular watering and with some organic matter/fertility in the soil.

You’ll know they are ready to harvest when the leaves die back and fall over. 

When choosing varieties to grow, you need to know the maximum daylight hours for your latitude as onions are daylight sensitive. We want to grow long day onions in our area. Look through our onion selection to choose your favorites. 

Here are some of our bulb onion varieties:

Alisa Craig	Short storage, sweet onion. Round shape, yellow skin
Red Geneva	Slower maturing but good storage. Slightly flatted shape, red skinned.
Dakota Tears	Good storage, disease resistant. Bright gold-red skin, round shape
Gladstone	Bunching onion with some storage ability. White skin, round shape
Borettana Cipollini	Sweet tasting, good storage. Red-pink skin with flattened shape.
Cortland F1	Disease resistant, storage variety. Gold skin, round shape.