GrowSabzHow to grow onion in pots
Also called Bulb Onion, Garden Onion, pyaaz, basal · Allium cepa
پیاز
- ☀️ Sunlight
- 6–8hours daily
- 💧 Water
- 0.8 Levery 3 days, 10 L pot
- 🌡️ Ideal temp
- 13–24°C
- 🪴 Min pot
- 10 L20 cm deep
- 🧺 Harvest
- 100–120days from sowing
- ⚖️ Yield
- 3 kgper 20 L pot
Onion grows well in containers given the right depth, consistent water and enough sun. From sowing to harvest takes about 120 days. The sections below cover the whole cycle — container size, exact watering amounts, feeding, what to watch for, and when to pick.
Short answer
Grow onion in a 10 litre container at least 20 cm deep, watering about 700 ml per 10 litres of soil every 3 days, and keep temperatures between 13 and 24 °C. First harvest comes 100–120 days after sowing.
Where to plant it
What size pot does onion need?
10 litres and 20 cm deep is the realistic minimum for a single plant. Pick a container below to see what changes.
| Container | Minimum size | Depth | Notes |
|---|---|---|---|
| Pot | 10 L | 20 cm | Ensure good drainage and adequate spacing for bulb development. |
| Grow bag | 10 L | 20 cm | Fabric bags promote air pruning and prevent waterlogging. |
| Open ground | — | 25 cm | Prepare well-drained, fertile soil. Space plants 10-15 cm apart. |
| Raised bed | 20 L | 25 cm | Excellent for drainage and soil control. Allows for optimal bulb growth. |
Watering
How often should you water onion?
Every 3 days through the growing season, at about 700 ml per 10 litres of soil — every 2 days in hot weather, every 4 days when it turns cool. Water in the early morning. Drip irrigation or base watering works best.
Too little water
- wilting leaves
- stunted growth
- small bulbs
Too much water
- yellowing lower leaves
- soft neck
- bulb rot
- fungus smell
Avoid: overhead watering (can cause fungal issues); soggy soil; inconsistent watering.
Climate
Can you grow onion where you live?
No hardiness zone needed — compare your actual temperatures against the plant's own limits.
| Ideal range | 13 – 24 °C |
|---|---|
| Survives | -5 – 30 °C |
| Germinates above | 10 °C — best at 20 °C, about 10 days |
| Flowers drop | above 30 °C |
| Sunlight | 6–10 hrs/day, best 8 |
| Frost | Medium sensitivity |
The flower-drop thresholds matter more than the survival ones. A plant can be perfectly alive at 30 °C and still give you nothing.
How cold is too cold for onion? Check your temperaturesEnter your night low and day high — see if it survives, and if it will cropTimeline
Onion growing stages, day by day
Click any stage to see what's happening. Durations shift with temperature — a warm season runs roughly a quarter faster than a cool one.
Feeding
Fertiliser schedule for onion
Feed on the interval below, changing what you give as the plant shifts from making leaves to making fruit.
| Stage | What to use | Per 10 L | Every |
|---|
How to prepare each feed
Common mistakes
Why onion fails, and how to avoid it
- A container that is too small
Below 10 litres the root run is too shallow. The plant grows, flowers late, and drops whatever it sets because it cannot support the crop.
- Watering too lightly
A daily splash wets the top few centimetres and nothing else. Onion wants about 700 ml per 10 litres of soil — one deep soak beats three shallow ones.
- Ignoring the flower-drop threshold
Above 30 °C flowers fall before setting. The plant can look perfectly healthy and still give you nothing — shade it through the hottest hours.
- Planting it beside Beans
Onions can inhibit the growth of beans and other legumes.
Companions
What to plant with onion
Good neighbours
Onions deter carrot rust flies, and carrots help loosen the soil for onion growth.
Onions deter common pests of lettuce, and their shallow roots don't compete with onion bulbs.
Onions deter pests like cabbage worms and loopers that attack brassicas.
Believed to improve the growth and flavor of onions.
Its strong scent can deter onion maggots and other pests.
Keep apart from
Problems
Onion pests and diseases
Each lists the weather that brings it on, so you know when to start checking rather than reacting once it's established.
Onion Maggot humidity any · temp 10-20
Larvae tunnel into onion bulbs, causing rot and wilting. Often attracted to damaged plants or freshly disturbed soil.
Thrips humidity <50% · temp >25
Tiny, slender insects that feed on leaves, causing silvery streaks, distorted growth, and reduced bulb size. Can transmit viruses.
Downy Mildew humidity >90% · temp 10-20
Fuzzy purple-gray growth on leaves, followed by yellowing and dieback. Favors cool, wet, and humid conditions.
Pink Root humidity any · temp 24-28
Roots turn pink, then purple, shrivel, and die. Leads to stunted growth and reduced bulb size. Favors warm soil and poor drainage.
White Rot humidity any · temp 10-20
Yellowing leaves, white fluffy fungal growth at the base of the bulb, often with small black sclerotia. Causes bulbs to rot in the field or storage.
Botrytis Leaf Blight Neck Rot humidity >80% · temp 18-24
Leaf blight appears as small white spots with a halo. Neck rot causes softening and decay of the neck during curing and storage.
Fusarium Basal Rot humidity any · temp >25
Yellowing and dieback of outer leaves, followed by a soft, watery rot at the base of the bulb. Favors warm soil temperatures.
Rust humidity >80% · temp 15-25
Small, orange-brown pustules appear on leaves and stems, eventually causing leaves to yellow and die prematurely.
Smut humidity any · temp 13-22
Dark streaks or blisters appear on leaves and scales of young plants. Infected plants are often stunted and may die.
Harvest
When to harvest onion
First picking falls between day 100 and day 120.
How to tell it's ready
- Tops fall over naturally
- Necks soften
- Outer skins develop color
How much to expect
Storing it: Cool, dry, dark, well-ventilated place (after curing)
Questions
Onion: common questions
How long does onion take to grow?
About 120 days from sowing to the first harvest, with picking usually starting between day 100 and day 120. Warm weather pulls that forward; cool weather pushes it back.
What size pot does onion need?
At least 10 litres and 20 cm deep for one plant. A raised bed wants 20 litres of soil and 25 cm of depth.
How often should I water onion?
About 700 ml per 10 litres of soil, every 3 days in normal weather — every 2 days when it is hot and every 4 days when cool. Water in the early morning.
Why is my onion flowering but not fruiting?
Almost always pollination. Onion carries separate male and female flowers and needs pollen moved between them — without insects, nothing sets. Hand-pollinate in the morning with a male flower brushed against the centre of a female one.
What temperature does onion need?
It does best between 13 °C and 24 °C and survives from -5 °C to 30 °C. Seed needs soil above 10 °C to germinate, ideally around 20 °C.
Can I grow onion in winter?
It tolerates cold better than most, down to about -5 °C, so a sheltered spot or a cold frame will often carry it through.
How do I know when onion is ready to harvest?
Tops fall over naturally; Necks soften; Outer skins develop color. Once picked: cool, dry, dark, well-ventilated place (after curing)