Onion Bulb Planting Instructions
Onions are a cold-season crop, easy to grow because of their hardiness.
We recommend using onion sets, which can be planted without worry of frost damage and have a higher success rate than direct seed or transplants.
Onions grow well on raised beds or raised rows at least 4 inches high.
Onions (Allium cepa) are one of the hardiest and easy-growing plants for the vegetable garden. Planting onion bulbs, or more commonly referred to as onion sets, is the fastest method for growing onions, which decreases the time from planting to harvest. Once harvested, yellow onions can be stored for several months in a cool, dark place.
The first thing you should do when planting onion sets is to amend the soil well with compost and organic matter where you intend to grow the onions. Onions enjoy fertile soil with very good drainage. Soil drainage is important for onions because if they stay too moist they could rot or mold could form on them.
Once you have the soil ready for planting remove the onion sets from the bag, and lay them out on top of the garden bed in the location where they will be planted. Onions do not need much spacing (depending on the variety) and can be planted fairly close together – about six inches apart.
Plant onion seeds 4 to 6 weeks before the last average frost—or even earlier indoors . When indoor seedlings are 2 to 3 inches tall, harden them off by exposing them to above-freezing night temperatures.
Outdoors, sow seeds thickly in rows about 1/2 inch deep. You can try mixing in radish seeds both to mark the planted rows and as a trap crop to lure root maggots away from the onions. Thin seedlings to 1 inch apart, and thin again in four weeks to 6 inches apart. For transplants or sets, use a dibble to make planting holes 2 inches deep and 4 to 6 inches apart. Use the closer spacing if you plan to harvest some young plants as green onions. For sets, open a furrow 2 inches deep and place the sets stem (pointed) end up 4 to 6 inches apart, and then fill in the furrow.
In general, onions grow best if you keep them well weeded. Use a sharp hoe to cut off intruders; pulling or digging weeds up can damage the onions' shallow roots. Once the soil has warmed, put down a mulch around and between the plants to discourage weeds and to hold moisture in the soil.
Dry conditions cause bulbs to split, so water when necessary to provide at least 1 inch of water each week; keep in mind that transplants require more water than sets do. Onions can't compete well with weeds, so it's important to direct water right to the onion roots