Onions are one of the staple ingredients in many dishes in Indian cuisine. It’s great fun to grow and harvest these onions from my container garden.

You can grow onions in a 5-gallon bucket and should be able to grow 6 to 8 onions. You can use a larger container to grow more. Make sure to provide the required moisture, light conditions, and nutrients. And check that there are sufficient drainage holes in the bucket.

I’ve written a detailed guide below on all the required things you need to do to successfully grow onions in your container garden. So keep reading.

When is the Best Time to Grow Onions?

Onions are a cool-weather crop. Ideally, you should plant them when the temperatures are still relatively cool. The right time for you will depend on where you live.

Generally, gardeners who live in regions with very cold winters should wait until early spring. You want the temperatures to be cool, but not so cold that the plant can’t flourish. Sometime around March or April is best. As long as the temperatures don’t drop below 28 degrees Fahrenheit, you should be good to go.

Now, those who experience milder winters may be able to plant much earlier. We’re talking late fall and early winter early!

The great thing about onions is that they sit dormant during the winter. In fact, these plants require a bit of exposure to the cold to reach their full potential. Unlike other plants, frost isn’t going to do a ton of damage. They won’t experience much growth. But once the weather warms up, they are ready to start growing!

If you’re starting the plant from seeds, you can start planting even earlier. Many gardeners will germinate the seeds indoors. This gives you the chance to start the plant several months before transplantation.

In those cases, you want to move the plant outside just before the last frost date. That early exposure to the cold will do the plants well.

How Long Do Onions Take to Grow?

Onions grow a bit differently than some other vegetable crops you might be familiar with. Like potatoes, yams, and carrots, onions are a root vegetable. That means that they grow under the soil where you can’t see!

The plant does have some hollow green foliage you can observe. But even then, the onion below can grow to be very big without you even knowing it.

On average, onions will require about 90 days to reach maturity after planting. Most of the growth happens in the spring after the weather turns.

Now, 90 days is just the average. There is no shortage of onion varieties out there. The exact timeline will depend entirely on the cultivar you choose.

For example, green onions are ready to harvest in as little as 20 days. Meanwhile, dry bulb onions can take as long as 175!

Plus, you have to factor in how you’re growing the onions. Plants started from seeds will take the full 90 days. But if you plant from onion sets, you’re looking at anywhere between 40 and 60 days!

How to Choose a Container for Onions?

Choosing the right container can make all the difference. As a root vegetable, onions need plenty of room to grow. But, they don’t require as much room as people think. The actual onion you eat takes up most of the space. Beyond that, the root system is relatively shallow.

At the very least, I recommend getting a container that has 10 inches of depth or more. With that depth, your onions are free to get as large as they can without having to worry about overcrowding.

Diameter isn’t a huge issue here. Depth is the most important factor, so feel free to get as wide of a container as you want.

Using standard 5-gallon buckets is a great choice for these plants. With a standard 5-gallon bucket from the hardware store, you can grow between 6 and 8 onion plants!

plastic containers
Plastic containers I used to grow plants

Buckets also have all of the hallmarks of a good universal growth container. They’re lightweight, durable, compact, and have a handle for easy transport. What more could you want? Grab a few buckets and you can have a healthy harvest without taking up a ton of space.

Other containers work well, too. Onions do just fine in plastic pots, bed-style containers, or terracotta pots. You can even use hanging planter boxes or simple plastic tubs. Just make sure that it has that required depth of 10 inches and the pot will work fine.

How to Prepare the Container for Planting

Before you start planting, there’s a bit of prep work you need to do.

While convenient, 5-gallon buckets aren’t built with container planting in mind. So, you’ll have to do a bit of modification.

The first thing you must do is to create drainage holes. If you were to plant onions in the bucket as-is, water would accumulate in the bottom. This could lead to fungal issues and rot.

Use a power drill to drive some holes along the bottom of the bucket. Make sure that the drill bit you use is large enough to let water seep through while still keeping the soil contained.

Arrange your drainage holes evenly around the perimeter of the pot. You should also place some holes near the middle. The goal here is to ensure that there’s no spot for water to collect. We want all of your onion plants in the bucket to receive the same amount of drainage capabilities.

After creating your drainage holes, you need to find a way to elevate the bucket. Most plastic 5-gallon buckets have a reinforced rim. While this makes it great for carrying heavy loads, it’s not exactly conducive to gardening. If you place the bucket directly on the ground, that reinforced rim can prevent water from flowing out.

Your easiest option is to use a couple of brick pavers. Arrange them so that they don’t cover the holes and you’re good to go. Many stores also sell plastic risers, which fit 5-gallon buckets perfectly!

How to Plant Onion Seeds or Seedlings

There are two ways to start your onion plant. The first is with onion seeds.

Growing from Seed

Seeds give you ultimate control. You can easily choose the cultivar you want and monitor growing conditions throughout every step of the growth process.

It’s best to start onion seeds indoors. Generally, 8 to 10 weeks before the last frost date is best. For most gardeners, this will be sometime around January or February.

Use a seed tray and some seed starting mix. Standard soil works well too. But, seed starting mixes have additional nutrients to help maximize germination rates. Moisten the growing medium and sprinkle the seeds evenly on top.

seed tray
Seed tray I bought for starting seeds

You can take a more uniform approach and try to position each seed about an inch apart. But, we’ll be thinning the herd later on. So, you can just sprinkle the seeds and try to germinate as many as you can.

Cover the seeds with about 1/8 of an inch of soil. Use your fingers to press the soil down a bit so that the seeds have full contact. Then, give the tray a good misting.

After your seeds are in the soil, cover the tray with a humidity dome and place them in a warm spot. Onion seeds will germinate in temperatures above 50 degrees Fahrenheit. However, temperatures closer to 75 degrees are best. Use a heating pad or put the tray on top of the refrigerator for additional warmth.

Growing from Seedlings

Your second growing option is to use a “seedling.” Onion seedlings aren’t like traditional plants. Instead of small sprouted seeds, you’re going to use onion sets!

Onion sets are small bulbs harvested early in the first year. Rather than waiting for the bulb to mature, farmers collect the sets and store them over the winter. This process creates fast-growing onion plants in the next growing season.

The best time to plant them is 2 to 4 weeks before the last frost date.

Fill your bucket with soil bury the sets no more than an inch deep. In a 5-gallon bucket, the onions will need about 3 inches of space between them. So, plant out your arrangement to plant the most sets you can in a single bucket.

How Much Sunlight Do Onions Need?

While they grow underground, onion plants still need a lot of sun exposure. These plants require full sun ever day. This isn’t a plant that you can put on a window ledge or under some shade.

Put the bucket on the south side of your house so that the plant can soak in the sun’s rays from dusk until dawn.

The key to growing large and healthy onions is to choose a variety that works for your region. There are three main onion types to choose from. The differences between these categories have to do with the amount of daily sun they require.

Short-Day Onions

Short-day onions require the least amount of sunlight to reach its full potential. These plants must get 10 to 12 hours every day. They do best in the South where days are a bit shorter.

You can grow short-day onions in the North with longer days. But, you will end up with smaller bulbs. Plus, the plant may start flowering much sooner.

Some common cultivars include Southern Belle and White Bermuda.

Long-Day Onions

Long-day onions are best for gardens in the North with much longer days. These varieties require 14 hours of sunlight every day. Anything less and the bulb will not form properly.

Cultivars like Yellow Sweet Spanish and Ring Master are long-day onions.

Neutral-Day Onions

Finally, we have the neutral-day onion. These varieties are a happy medium between long-day and short-day onions. Best for the mid-west and mid-east regions, these onions need between 12 and 14 hours of sun a day for bulb formation.

You can try popular neutral-day onion varieties like Cabernet and Early Yellow Globe.

How to Water the Onion Plant

Onions are water-loving crops. In total, these plants need 30 inches or more of water every growing season!

When you grow in 5-gallon buckets, you have to be extra vigilant about watering. Container-grown onions don’t have access to stored moisture in the soil like those in the ground do. As a result, they’re prone to drying out much faster.

Water your onion plants frequently to keep the soil moist. About 2 to 3 inches per week is ideal. You can spread the waterings throughout the week based on your plant’s needs.

If you’re not sure about whether or not your onion plant needs hydration, do a quick soil test with your finger! Stick your finger into the soil near your plant. You only need to bury your finger up to the first knuckle. If the soil feels dry to this depth, it’s time to water your plant!

Water the plant deeply and make sure that it’s able to drain properly.

Don’t go overboard! Excessive watering could lead to fungal diseases and rot.

How to Thin the Onion Seedlings

If you grow your onions from seed, thinning is an essential step in the process. You don’t have to worry about this if you use onion sets. But tiny seedlings need thinning to avoid overcrowding.

The goal of thinning is to provide enough space for the strongest plant to grow.

The best time to start thinning is when the seedlings are about 2 to 3 inches tall. Examine your seedlings clusters and identify the strongest baby plants. Those are the ones you want to keep. Remove everything else by clipping the plants at the base of the soil.

You can thin the onion plants so that they are all about 1 inch apart. In about 4 to 6 weeks, you can thin again until the seedlings are at least 3 inches apart.

How to Fertilize the Onion Plant

Despite the shallow root system, onions are heavy feeders. The plants take advantage of as many nutrients in the soil as they possibly can. Fertilization helps to improve soil quality and give the plants a boost while growing.

Onions require all of the big-three nutrients. This includes nitrogen, potassium, and phosphorus. The plants absorb a moderate amount of nitrogen. But, they enjoy higher levels of potassium and phosphorus!

Generally, standard nitrogen formulas work just fine. An organic 10-10-10 fertilizer works best. I recommend using a nitrate-based formula rather than a sulfate-based one. Sulfates tend to make the resulting harvest more pungent. We want a sweet and flavorful onion, right? Use nitrate-based fertilizers to achieve that.

Use a water-soluble fertilizer to side-dress the onions about 3 weeks after planting. Then, you can apply additional applications every 2 to 3 weeks throughout the growing season.

How to Prune the Onion Plant

I know what you’re thinking: Why do I need to prune an onion?

Well, pruning can be very beneficial to your final harvest. It makes sense when you think about it! Onions are root vegetables. The goal is to make the root crop as big as possible. So, why let the plant waste energy on producing more foliage?

Pruning allows you to divert the plant’s energy back to the vegetable.

You can prune the plant several times before harvest. The first pruning should occur when the stalks get to be about 9 inches tall. Simply snip the talks at a 45-degree angle in the middle. Cut them in half so that about 4.5 inches remain.

Then, let the stalks continue to grow. The second pruning will occur when the stalks reach 12 inches in height. Again, cut the stalks in half so that only 6 inches remain.

Continue this cycle until the onion matures. Alternate between letting the stalks grow to 9 and 12 inches. Generally, it will be about three cycles before the onion is ready to harvest.

How to Harvest Onions from the Bucket

After about 90 days of coddling your plant, your onions are ready to enjoy. But how do you know when to harvest them?

You can’t check the vegetable. So, you have to rely on the appearance of the stalks.

Usually, onions are ready when the stalks start to dry out and turn yellow. They will flop over, indicating that the onion is ready.

To harvest them, simply pull the vegetable out by the stalk. Give the onion a good shake to knock off any soil and set them to the side.

Don’t cut the tops off just yet! Onions need about 7 to 10 days to cure. The curing process helps to seal and develop the flavor. When you first pull the vegetables out of the soil, you’ll notice that the skin is thin and fleshy. At this point, the vegetable is quite delicate.

Curing will address these issues. You want the skin to dry to the signature paper consistency. The roots and neck of the vegetable will dry out as well to seal the flavor in.

Once the onion is properly cured, you can clip the roots and tops off. Then, it’s just a matter of finding the perfect recipe to enjoy them

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