Crop profile

Onion crop profile

A long-cycle bulb crop with simple care, best set in clean rows and kept free from competition.

Italiano

Starting method

Direct sowing or transplanting

Direct soil

2 °C

Transplant soil

2 °C

Night minimum

-2 °C

Frost buffer

-30 days

Heat stop

30 °C

Harvest

90–150 days

Indoor lead

77 days

Key temperatures

0
5
10
15
20
25
30
35
40 °C

Below 2 °CCold risk: slower growth or cold damage.
2 °CMinimum range to start: direct sowing from 2 °C, transplanting from 2 °C.
2–25 °CBest range for growth and production.
25–30 °CPerformance drops and plants move into stress.
Above 30 °CPause transplants: heat stress risk.

Onion cycle

1. Start indoors
Average time:
77 days
2. Direct sowing or transplanting
Soil: at least 2 °C
Night minimum: at least -2 °C
3. Growth
Ideal temperatures 2–25 °C
Avoid peaks above 30 °C
4. Harvest
First harvest around:
90–150 days after starting

How to start

Recommended method: direct sowing or transplanting.
Prepare seedlings with mild, steady temperatures.
Start when soil and nights are stable above the crop thresholds.

Temperatures to respect

Direct-sowing soil: minimum 2 °C.
Transplant soil: minimum 2 °C.
Night minimum: minimum -2 °C.
Heat stop: 30 °C.
Suggested frost buffer: -30 days.

Harvest timing

Cycle to first harvest: about 90–150 days.
Harvest gradually as produce reaches maturity.

Seasonal notes

Protect young plants from late frosts and thermal swings.
In summer, avoid water stress and heat peaks above 30 °C.
Steady growth improves development and harvest quality.

FAQ and sources

When should you sow or transplant onions?

Onion is very tolerant of cool conditions: it can start with soil around 2 °C and nights slightly below freezing. You can direct sow, raise transplants, or use sets, depending on season and goal. From seed it is slow: for transplanting, the seedbed can start about 77 days earlier. The cycle is long, 90-150 days. Autumn sowing and transplanting are possible with suitable varieties and well-drained soil.

Are onions better from seed, transplants, or sets?

Seed gives more variety choice and costs little, but it takes time and nursery care. Transplants are a good compromise: they establish well and make tidy rows. Sets are the easiest method for beginners, but they can bolt more easily after stress or cold. For large bulbs, choosing varieties suited to your local day length matters more than the starting method. In every case, keep the bed clean of weeds.

When are onions ready to harvest?

Onions are usually harvested 90-150 days after sowing or transplanting. The practical sign is foliage that yellows and bends down naturally. At that point, reduce watering and harvest on a dry day. Dry the bulbs in a ventilated place, protected from rain and harsh sun. Good curing is essential for storage: an onion harvested mature but dried badly is much more likely to rot in storage.

Why do onions stay small?

Onions stay small because of late sowing, the wrong variety, weed competition, lack of water during bulbing, or poor soil. Onions have narrow leaves and compete badly: if the bed is weedy, they lose strength quickly. Spacing also matters: crowded plants make small bulbs. Keep moisture steady until bulbs swell, then reduce water toward maturity. Avoid late nitrogen, which keeps leaves green but lowers storage quality.

Can onions be grown in autumn?

Yes. With suitable varieties, onions can be grown in autumn. The young plants need to root before cold weather, then restart in spring. The advantage is an earlier harvest and use of cool soil; the risk is winter waterlogging. Use well-drained beds, do not overfeed, and control weeds even in cold months. If your area has severe frosts, protect young plants with horticultural fleece during the most delicate stages.