Growing Onions Indoors

Growing Onions Indoors

Last Updated On: December 5, 2022

Onions are a staple in most kitchens due to their versatility when cooking and wide variety of flavors. They can be added to soups, stews, burgers, salads, pasta, and many other dishes. As one of the most-used vegetables in your home, you may want a steady supply throughout the year. To ensure you always have a few on hand, it may be a good idea to try growing onions indoors. Doing so isn’t all that difficult, as long as you create the right growing conditions for onions inside. For more information, keep reading.

Onions Quick Overview

  • Onions are a relatively easy plant to grow, but can take up a good deal of space.
  • Opt for a wide, shallow container as most onions don’t develop large root systems. Do ensure there is enough room to cover the onion bulb though.
  • Sunlight is the primary issue for indoor grown onions as most varieties need at least 12 hours per day.
  • Water them when the top inch of the soil is dry. Onions like damp but not soaked soil.
  • Onions take 3-4 months to mature, at which point you can gently pull them out of the soil.


One of the reasons onions are so popular is due to the variety of options available. In fact, there are six kinds of onions to choose from, including yellow, white, red, sweet, shallots, and scallions. Each type has further varieties to pick from, each with a unique flavor that can accentuate your meals. With all these onions available, you have an almost unlimited supply to add to your garden and unlimited options in your cooking.

When choosing your indoor onions, you may also want to consider their indoor growing location. Long-day onions need a few more hours of sunlight than short-day varieties, so this is something to think about when deciding which to grow. In general, most onions have similar care, but always make sure to research the specific variety to ensure you can keep up with its needs. As a last bit of advice, the smaller the variety the easier of a time you’ll have growing it indoors.

Soil And Container

Onions aren’t picky about the materials used for their containers, so you can use anything on hand, as long as it has enough room for these veggies to spread out. Though they have shallow roots, small or regular varieties require depths of at least six inches, while giant varieties need ten inches or more.

Onions prefer about three inches between each plant, so the more you wish to plant, the wider the container you’ll need. Be sure to add drainage holes to your chosen container for proper drainage. Our top choice is terra cotta as it’s cheap, easy to obtain, and helps prevent overwatering. If you’re not sure which type of container to pick, you can’t go wrong with it.

Like with their containers, onions aren’t particular about the soil they’re grown in. Any nutrient-rich option will give them what they need, though it’s best to use soil with a pH of 6.5 or higher for the happiest plants. Most commercial potting soils will work perfectly fine for almost any variety of onion.


As long as you have the proper container and soil, planting your onions is relatively easy. You can plant seeds, which adds a few extra weeks of growing time, or sets, which are mature onions forced into dormancy.

Seeds need to be sown about half an inch deep and a few inches apart to give them room to grow. Bulbs need to point up with the roots on the bottom. Onion sets also need at least three inches between each plant, though they should be planted about an inch deep since they are already established plants.

Onion Seed Variety Pack

Light And Location

Unlike some plants, onions love plenty of full sunlight. Short-day varieties need at least 12 hours of direct light each day, while long-day onions need a minimum of 14 hours of light. To ensure they’re getting enough light to thrive, you’ll need to place your plants near a window that can accommodate their needs. South-facing windows are best since they get the most sunlight each day.

If you live in a northern climate with shorter fall and winter days, you can supplement the light. Onions can get what they need from most commercial grow lights, so you can pick the right option for your home. This is often the trickiest part of growing onions indoors, so if you can nail the light it’s smooth sailing from here.

Water And Fertilizer

Onions like to be damp, though they hate soaking in too much moisture. It’s best to add water on a weekly schedule, checking the soil in between to be sure it isn’t drying out. Generally, wait until the top inch of the soil is dry to the touch before adding water. This helps ensure that the soil has dried out a bit between waterings, which helps prevent issues like root rot.

For fertilizer, choose one that is nitrogen-rich to encourage larger growth of your onion bulbs while strengthening their shallow root system. You can dilute this down to about half strength for container grown onions, and apply about once per month during the growing season. During the winter/fall you can stop fertilizing as your plant will grow more slowly and not need the added nutrients.

Temperature And Humidity

As one of the hardiest vegetables, onions can tolerate varying temperatures. They grow best between 55 to 75 degrees Fahrenheit, though they can handle cooler or hotter days when needed. They don’t like too much humidity, though. For happy plants, you’ll need to keep your onion-growing area at about 30% to 50% humidity. Both these values are well within the normal range for most homes, so it’s unlikely you’ll have a problem with either of them when growing onions indoors.


Since onions grow beneath the soil’s surface, it can be hard to know when they’re ready for harvest. The best way to tell is by checking the foliage on top for soft spots, yellowing, or bending. These are all signs of a mature onion plant ready to be harvested. You can also partially uncover your onions to see if they’ve grown to the size you’re looking for.

It can take 3 to 4 months for onions to fully mature after planting, so it’s a good idea to mark the plant date on a calendar to make sure you’re not digging them up too soon. You should also take into account your onion’s variety as these can lead to slightly different maturity times.

Harvesting is easy, too, since it only requires loosening the soil around the onion and pulling it out. If you stagger your planting, you’ll have a steady supply of onions to harvest throughout the year.

Growing Onions Indoors

Growing onions indoors is an easy task since these plants don’t require a lot of pampering. As long as you provide them with the right container size and plenty of light, your indoor onions should thrive for year-round use.

Frquently Asked Qusetions

What Are Common Onion Pests?

There are two types of pests that favor onion plants. Thrips are sucking insects with long, slender bodies that cause streaks, white patches, or silver speckles on onions. Onion maggots lay their eggs on plant bases, which hatch and feed on the plants. These are both rare for indoor plants though.

How Do You Store Harvested Onions?

After harvesting your onions, lay out the ones you won’t use right away to cure. Then place the onions in a mesh bag or layer them in a box. Store them in a cool, dry place that maintains a temperature of 40 to 60 degrees Fahrenheit. Do not store your onions in the fridge since the conditions are too damp to keep onions for long.

Can Onions be Grown in Water?

Yes, onions can be grown in water using seeds, sets, or even onion scraps, though they may not grow as large as they would in soil. Place your chosen onion starter in a glass or bottle and add enough water to cover the roots. Add more water as needed to keep the roots damp. New sprouts will grow, which can then be used in any of the recipes you have in mind.

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