Onions are a cold-season crop, easy to grow because of their hardiness.
Typically, onions are planted early in the spring and harvested in the fall after their tops begin to die back. In the southern U.S., some onion varieties can be planted in the fall.
Onions and milder-tasting shallots are one of the easiest crops you can grow. You can raise them from seed, but it’s so much simpler and quicker starting with sets (small onions) that you grow on to cooking size.
They can be stored over winter thus making a versatile crop. They are used in a huge range of culinary dishes, both raw and cooked and are quite easy to grow.
Types of Onions
Onions come in a wide variety of shapes, sizes, and colors. The white, yellow, or red bulbs range in size from small pickling onions to large Spanish cultivars; they can be globe-, top-, or spindle-shaped.
Most types can be pulled young as green onions, but there’s also a perennial bunching type called Allium fistulosum that’s practically disease- and insect-proof and produces superior scallions.
Each bulb of the multiplier or potato onion multiplies into a bulb cluster. So with every harvest, you’ll have bulbs to replant for a continual supply.
The Egyptian or top onion produces a bulb cluster at the end of a long stem with a second cluster frequently forming on top of the first. It also has an underground bulb, which is often too pungent to eat.
HOW TO GROW ONIONS
You can plant onion and shallot sets in early spring or autumn; from an autumn planting, you’ll get earlier, heavier crops. Both like the sun and a moisture-retentive, fertile soil, ideally with plenty of well-rotted organic matter such as garden compost.
It’s worth looking for heat-treated sets, as the resulting plants are less prone to bolting (producing flowers). Bolting reduces the quality of the crop.
Onions will grow in almost any soil from sandy loams to heavy clay. The soil should be firm. If your soil is heavy then you can introduce some organic compost or manure into the soil to help its moisture-retaining properties.
Onions prefer a slightly acidic soil – PH 5.5-6.5 is a good PH for growing onions.
When to plant?
Generally speaking, plant onion sets outdoors when the weather is cool—not cold. Ideally, outdoor temperatures shouldn’t dip below 28°F (-2°C) after planting
If planting from seeds, start them indoors about 6 weeks before you plan to transplant them to the garden. Onion seeds need temperatures of at least 50°F (10°C) to germinate properly.
How to plant?
Onions can be planted from seed or sets (small partly grown onion bulbs). Sets are more expensive but they tend to be more reliable in their results and also require less work – no thinning and reduced onion fly risk.
If sowing from seed then sows in drills about 2cm deep with about 1 inch between seeds. If sowing in rows then spaces the rows about 30cm apart.
The soil should be moist before sowing so check the soil the day before sowing and water if the soil is dry.
If planting onion sets then they can be planted around Mid to Late March. Again space rows about 30cm apart. Sow sets around 10cm apart as they shouldn’t require any thinning. Dig a small hole for each set and place the set in neck upwards. When covered back up with soil the tip of the neck should just show through the soil surface.
Spring onions (scallion) can be sown from April and planting should be staggered every few weeks to ensure a continuous crop throughout the growing season.
How to care?
Watering
To water onions efficiently, extend soaker hoses along the row close to the plants. Or open a small trench between rows and fill it with water. This keeps the roots supplied while leaving most of the soil surface dry, inhibiting weed seed germination.
Onion Flower Stems
Break off any flower stems which may appear, this is the onion trying to bolt. A hard stem will be produced inside the onion making it unsuitable for storing. Breaking the stem off will not prevent this from happening but will stop the onion using the energy in the bulb to produce a flower. The bulb around the hard stem will still be fine but should be used when pulled.
HOW TO HARVEST ONIONS
Once onion tops turn yellow, use the back of a rake to bend them over horizontally. This stops the sap from flowing to the stems and diverts the plant’s energy into maturing the bulb. A day or so later, when the tops turn brown, pull or dig the bulbs on a sunny day, and leave them to dry in the sun. Lay the tops of one row over the bulbs of another to help prevent sunscald.
When the outer skins are thoroughly dry, wipe off any soil and remove the tops—unless you intend to braid them. Store in a cool, dry place; hang braided onions or those kept in mesh bags in an airy spot. Such dried bulbs will keep for about 4 months to 1 year.