How to Grow Onions - The Complete Guide

Onions are a rewarding vegetable to grow at home and an excellent addition to any garden. Below we share the basics of growing onions in a home garden, as well as common mistakes and considerations.

When to Plant Onions

Onions are a frost tolerant vegetable. This means the best time to plant them is mid to early spring, and mid to late summer for a fall harvest. If you’re expecting a late or early frost after planting, protect your onions with a blanket of straw or cover them with plastic buckets.

If you live in the U.S., check out the Farmer’s Almanac or the USDA’s Plant Hardiness Zones for more help regarding frost and the best dates for planting in your area.

How to Plant Onions

Plant your onion seeds directly in the soil of your garden or container at a depth of 0.5 inches (1 centimetre). Seeds can be planted outside or you can germinate them indoors and transplant them later. Typically, onion seeds take about 1 - 2 weeks to fully germinate.

If transplanting, the best time to move onion plants outside is when they reach 3 - 4 inches (7 - 10 centimetres) tall or have at least 3 - 4 true leaves.

When planting onions in the garden, it’s best to space them 1 - 2 feet (30 - 60 centimetres) away from the nearest plant.

Interested in Container Gardening?

Join the Garden Auntie newsletter!

Get expert tips, tricks, and inspiration for successful container gardening no matter the environment. Create a stunning and thriving garden, even in small spaces!

How to Grow Onions in Pots

The key to caring for onions in containers is well draining soil and a pot big enough for their root system. Aim for a pot that is roughly 288 cubic inches (4,719 cubic centimetres) in size. Any old flower pots you have lying around should do the trick.

For more in depth information, check out our full guide on growing onions in containers.

How Long do Onions Take to Grow

On average, it takes about 100 days for planted onion seeds to develop into a fully mature plant.

How Big do Onions Get

Typically, onion plants reach about 1 - 2 feet (or 30 - 60 centimetres) in height. Though this can fluctuate depending on the variety.

How Much Sunlight do Onions Need

Onions need at least 6 hours of direct sunlight every day in order to thrive. Be careful to place your plants in an area that receives adequate sunlight. Otherwise, they may not mature properly.

How Much Water do Onions Need

Onions like well draining soil that is kept consistently moist, but not wet or soggy. The amount of water it takes to achieve this effect will differ depending on the type of soil available to you.

Be sure to water your onions on a consistent, steady schedule. This will ensure the plant yields a healthy, uniform crop.

If growing your onions in pots, they will need to be watered more frequently than onions planted directly in the garden.

You will know your onions are in need of more water when their leaves wilt, yellow, and/or the plant begins to droop. But be careful, this can also happen if the plant receives too much water. This is a difficult balance for most novice gardeners. But the more time you spend with your onions, the better you’ll be able to gauge how thirsty they are.

How to Harvest Onions

Onions are ready to harvest when their tops turn yellow and begin to fall over. Although, you can harvest them at just about any stage before if you don’t mind smaller bulbs. To harvest, use a garden spade or fork to loosen the soil around the onion. Firmly grasp the base of the stem and lift the onion out of the ground.