Growing Onions: What Matters From Seedling to Cure
Onions are one of those crops that look simple but reward attention. They take months to grow, and for most of that time, they look like nothing more than green blades sticking out of the soil. Then, near the end of the season, the tops fall over, the bulbs swell and you have a harvest worth waiting for.
At Raikana Primary School in Pretoria, we grew our onion crop from seedlings planted into raised beds prepared with chicken feather fertilizer and covered with grass mulch. The result was a strong harvest of golden bulbs with clean, healthy roots.
This article walks through the full journey, from the seedling tray to the harvested bulbs. If you want to see how we grew our garlic crop alongside the onions, I covered that in how to grow garlic from sprouted cloves to harvest. The two crops grow well together and follow a similar rhythm.
In This Article
- Why onions are worth growing
- Starting onions from seedlings
- Preparing the bed
- Planting the seedlings
- Early growth and weeding
- Watering onions
- When onions are ready to harvest
- How to harvest onions
- Curing onions for storage
- What I learned from growing onions
Why Onions Are Worth Growing
Onions are one of the most useful crops in a kitchen. They store well, they are used in almost every meal and they can be grown in a relatively small space. A single bed of onions can keep a family supplied for months.
The crop is also forgiving. Once the seedlings are established, onions need very little attention beyond weeding and steady watering. If the soil is prepared properly and the plants are not stressed, they will do most of the work themselves.
For us at Raikana, the onion crop has become one of the most reliable parts of the garden. It grows well alongside the garlic and leeks, and it fits neatly into the rotation we use across our raised beds.
Starting Onions From Seedlings
Onions can be grown from seed, but they take a long time to get going. That is why most gardeners start them in a nursery tray or seedbed first, then move them into their final position once they are strong enough to handle it.
We started our onions in a red plastic nursery tray filled with a light compost mix. The seeds were sown thickly, watered gently and kept in a sunny spot until they germinated.
Onion seedlings grow as thin green blades. They look more like grass than vegetables at this stage. The goal is to let them grow to about 10 to 15cm tall before transplanting, so they have enough structure to survive the move.
Preparing the Bed
Onions need loose, well-drained soil with plenty of organic matter. The bed should be prepared before the seedlings go in, so the roots have somewhere soft to grow.
Our onion bed had already been prepared for the season. It was fed with chicken feather fertilizer and covered with a thick layer of grass mulch. The feather compost released nitrogen slowly through the season, and the mulch kept the soil cool and moist.
Onions do not like to compete with weeds, so a clean bed is important. Remove any existing weeds before planting and make sure the soil surface is level enough for the seedlings to sit evenly.
Planting the Seedlings
When the seedlings are ready, they need to be lifted from the tray, separated gently and planted into the bed.
The spacing matters. Onions should be planted about 10 to 15cm apart in rows, with about 30cm between rows. This gives each plant enough room to form a bulb without competing with its neighbour.
Each seedling is planted about 2 to 3cm deep. The roots should be fully covered, and the green blade should stand upright above the soil. The base of the seedling, where the bulb will eventually form, should sit just at or slightly below the surface.
If the bed is mulched, move the mulch aside to plant, then pull it back around the seedling. Keep the mulch a small distance from the stem so the plant does not rot.
Early Growth and Weeding
In the first few weeks after planting, the onion seedlings are vulnerable. They need steady moisture, good sunlight and a clean bed free of weeds.
Onions are not strong competitors. If weeds are allowed to establish, they will take nutrients and water from the seedlings and slow the crop down. Regular weeding is one of the most important jobs in an onion bed.
Weeding should be done by hand or with a small tool. Onion roots are shallow, and a deep hoe or fork can damage the bulbs forming underground. Pull weeds gently from the base, taking care not to disturb the onions.
The mulch layer helps here. A thick mulch suppresses most weeds before they can establish, which saves time and protects the shallow roots.
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Watering Onions
Onions need consistent moisture through most of their growth cycle. But the watering changes as the crop matures.
During the main growing season, water the bed deeply once a week. A slow, deep soak encourages the roots to grow down and out, which supports stronger bulb formation. Light daily sprinkles only wet the surface and do not reach the roots.
The grass mulch on the bed is important here. It slows evaporation, keeps the soil cool and holds the moisture from each watering. Between the mulch and a weekly deep soak, the onions receive enough water without the soil ever becoming waterlogged.
Once the tops start to fall over and dry, stop watering. Too much water at this stage can cause the bulbs to rot in the ground. Onions that are allowed to dry out naturally at the end of the season store better and last longer.
When Onions Are Ready to Harvest
Onions are ready to harvest when the tops fall over and start to dry. This is not a sign of a dying plant, it is the sign that the bulb is fully formed and ready to be lifted.
The timing is important. If you harvest too early, the bulb will be small and the skin will be thin. If you wait too long, the bulb can start to split and lose its protective skin.
We harvested ours when the tops had fallen over and about half of the leaves were dry and brown. The remaining green leaves were still attached, but the outer ones were starting to curl and die back. This is the sweet spot.
How to Harvest Onions
Harvesting onions is simple, but a few small details make a difference.
Use a garden fork to loosen the soil around the bulb. Then gently lift the onion out of the soil by the base of the stem. Do not pull the plant by the leaves, or you may tear the stem from the bulb.
Shake the loose soil off the roots, but do not wash the bulbs. The papery skin is delicate, and washing can damage it. Leave the onions in a dry, airy spot to cure for two to three weeks. Curing hardens the outer skin and helps the onions store for months.
The Harvest
Harvest day is one of the best moments in the garden. After months of waiting, the tops fall over, the bulbs are exposed and you finally get to pull them out of the ground.
A good onion harvest is easy to recognise. The bulbs are firm, heavy and well-formed. The papery skin is intact and clean. The roots are dry and easy to trim.
We harvested ours in batches, lifting a few bulbs at a time as they matured. Some were eaten fresh. Others were cured and stored for the months ahead.
Curing Onions for Storage
Curing is the process of drying the onions after harvest. It hardens the outer skin, seals the neck of the bulb and helps the onion store without rotting.
To cure onions, lay them out in a single layer in a dry, airy spot. They need good airflow around each bulb. A shaded porch, a dry shed or a well-ventilated garage works well.
Leave them to cure for two to three weeks, or until the skin is dry and papery and the neck of the onion is fully closed. Then trim the roots and the dried leaves, and store the onions in a cool, dark place in a mesh bag or a basket.
Properly cured onions can last for months. That makes them one of the most useful crops to grow, even in a small garden.
What I Learned From Growing Onions
Onions taught me that the simplest-looking crops often require the most care. Here are the main lessons from this crop:
-
Start with strong seedlings.
Healthy seedlings that reach 10 to 15cm before transplanting establish faster and produce stronger bulbs. -
Prepare the bed properly.
Loose, well-drained soil with plenty of organic matter gives the bulbs room to grow. -
Keep the bed clean.
Onions do not compete well with weeds. Regular hand weeding is one of the most important jobs in an onion bed. -
Water deeply, not often.
A weekly deep soak is better than daily light sprinkles. It encourages deeper roots and stronger bulbs. -
Stop watering before harvest.
Once the tops start to fall over, stop watering. Too much water at the end can rot the bulbs. -
Harvest at the right time.
Wait for the tops to fall over and start drying. Do not wait too long or the bulbs will split. -
Cure before storing.
Dry the onions in a cool, airy spot for two to three weeks before storing. This hardens the skin and helps the onions last for months.
Gardening Lesson
Onions reward patience and a clean bed.
Start with strong seedlings, keep the weeds down, water deeply and wait for the tops to fall over. Cure the bulbs before storing and you will have onions that last for months. There is nothing complicated about it, but every step matters.
Soshanguve, Pretoria, South Africa
Growing Knowledge. Growing Food.