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How to Grow Onions in a Raised Bed (Step-by-Step Instructions)?

Raised beds are popular among gardeners who have limited space or poor soil. With a few precautions, onions can be grown successfully in raised beds. However, there are various types of onions. This article will show you how to plant these various types of onions in a raised bed of soil.

Growing onion in raised bed.

To plant your own onions is liberating, especially since it’s such an easy seed or vegetable to propagate. Use onion seeds, onion sets, or the ends of old onions to replant more fresh onions. I do this with my green onions all the time. You can double the yield on a single onion every single time when planting in a raised bed with these tips.

But first, here is a quick reminder of the differences between onions. This will help you decide on which onions you want to plant in your raised outdoor garden. Next, there are instructions on how to use these different types of onions to plant these alliums in a raised bed of soil. 

Different Types of Onions to Plant

Scallions and Chives

Freshly harvested scallions.

The easiest and fastest onion to replant is a green onion, also called a scallion. These are long, thin tubular onions with a tiny white bulb at the end of a long green stem. Store the scallions whole in the refrigerator with the roots in a jar of water.

Cover loosely with a plastic sandwich bag to store for longer than a week. Replace the water weekly. Cut off the green ends of the scallions when ready to use, but save the white root ends in the water to replant.

You also see these sold as chives in stores, but chives typically do not have the bulb on the end. In order to replant scallions, chives, or other long, green onions, you must have the root tip. Otherwise, it will not regrow roots and be a viable plant. Dried chives are well chopped up and stored in the spice cabinet. Use these in place of onions and scallions in potato, egg, or tofu dishes that need a boost of flavor.

Yellow, Red, and White Round Onions

Yellow, white and red onion on table.

The other type of onions you can plant on the ground are globular shaped bulbs large enough to slice into thick rings. When purchasing onions to use for growing onions, you will see these identified by color most often. The coloration plays a role in the types of minerals and vitamins, as well as the flavor profiles, of each type of onion.

Healthline reports, “Onions are rich in plant compounds and antioxidants, especially quercetin and sulfur-containing compounds. Colorful varieties, such as yellow or red ones, pack more antioxidants than white ones.” Of these, red onions are more nutritious based on the more vibrant purple and red tones coming from the antioxidant, anthocyanin. 

According to Womens Health Mag, “A 2017 study published in Food Research International found that red onions were most effective at killing human cancer cells compared with other onions thanks to their higher levels of the antioxidants quercetin and anthocyanin.” Red onions tend to last for about a month stored in a cool, dry pantry.

As for white onions, these tend to be hotter or spicier in flavor, especially when eaten raw. This makes the white onion rarer and less popular for home cooks. Look for a large, white onion bulb covered in white translucent skin. Store the white onions in your pantry in a dark, cool place away from potatoes.

A yellow onion with a light brown skin is most commonly seen as a sweeter onion. Popular varieties of yellow onion include the Vidalia that can only be grown legally in South Georgia, as well as Walla Wallas and Mauis. These onions are grown seasonally and are the least shelf stable. Store yellow onions in your refrigerator bin for up to a week at most before they lose their crisp texture and start to go bad.

Onion Sets and Shallots

A hand with gloves planting sprouted onion in raised bed.

Here is an interesting type of onion that is the first on this list that you won’t see on a salad. An onion set is an onion that is specifically grown to be used in gardens, including raised beds. When you buy an onion set, you get a small bulb on the end of a green plant that has been grown specifically to be planted in the ground. Unlike onion seeds, an onion set has already developed as a plant and takes less time to mature. 

You might also see small round onions similar in size to onion sets sold in grocery markets. These are baby or pearl onions, and may also include medium sized tear-drop shaped onions called shallots.

The shallot is an onion prized for its mild flavor and interestingly shaped rings. Shallots to replant into new onions, too, as the only variety to regrow up to a dozen new onions per bulb. Store shallots in a dry, cool pantry for up to two months.

When to Plant Onions in Raised Beds Outdoors?

The best time of the year to plant onions in the dirt of a raised bed outdoors is in the spring. However, thanks to their short growing season, you are able to plant onions in raised gardens in the summer and fall, too. 

Planting Onion Seeds in Raised Beds

A woman's hand holding onion seeds.

For most conventional gardeners, the traditional way to plant a garden is with seed. This can also be the cheapest. A pack of 100 onion seeds can be as cheap as 50 cents in some variety shops or home and garden stores.

Here are the step by step instructions on how to grow onions starting from seed. These instructions are also applicable to the other types of onions as discussed previously. Following the instructions are details about how to replace seeds with onion sets or old onions.

How to Plant Onions in a Raised Bed (Step by Step)

Step 1: Soil Preparation

Take your soil from the raised bed and use compost to supplement the top layer. Mix thoroughly a day before planting your seeds for the best boost in growth. Wet well the day prior, as well, to ensure a moist top layer. Moisture is essential to having a well developed root system, as onions have a very shallow root system.

Step 2: Lay Out Rows

Line out rows that are 12 inches apart and sprinkle onion seeds along the line. Use a landscaping chalk line, if available, or a thin rope stretched from end to end for each row. 

Step 3: Plant Seeds

Use a small tool to push each seed into the soil about one inch. Water well and within a week you will have harvestable onion sprigs. 

Step 4: Thin the Plants

To allow the onions to continue to grow, remove the weakest shoots to eat as scallions or chives. From there, reposition the largest shoots so that each onion plant is spaced six inches apart in each row. 

Step 5: Harvesting Onions

Grow until the shoots of the onions begin to turn brown and dry out, causing them to fall over. This is a sign that your large, bulbous onions are fully grown and ready to harvest

Pull up each onion and allow it to “cure” for up to two weeks in a completely dry, dark room. Bonnie Plants explains, “ As the onions cure, the roots will shrivel and the necks above the bulbs will slowly dry – a natural process that helps to seal the top of the bulb, making the onions less likely to rot.”

This is when the onion closes the water and air flow to the root stem and crown, protecting against mold and insects. Cut off the shoot end and toss out, leaving the round onions unwashed with all of their skins intact until ready for use.

Planting Onions from Onions in a Raised Bed

Scallion plants in raised bed.

Step 1: Using Onion Cuttings

When using existing onions to plant a new crop of onions, start with cuttings that include the root ends. This can be the bottom of an onion you use for a meal. 

Step 2: Grow Scallions

Take this and stick it in a shallow bowl of water with the roots sticking down into the water. Allow the sunlight to heat up the roots and start the growth process. Once the roots have grown a green shoot that is about 9 inches long, remove the onion cutting from the water. 

Step 3: Transplant Scallions 

Take a sharp knife and cut open the onion, by slicing it in half lengthwise. Remove the rooted shoot and you have a new onion plant that is ready to plant immediately. 

Step 4: Plant Scallions

Following the spacing guidelines of foot-wide rows with onions spaced every half a foot, plant the onion shoots whole with the roots down into the soil of the raised bed. Avoid letting the soil touch more than the white part of the bulb to prevent root rot and mold from toppling your scallions. 

Step 5: Water Until Harvest

Water when the soil surface is dry, and avoid saturating the raised beds. The onions will be ready to harvest in about three to six months as whole round onion bulbs.

Planting Onion Sets in a Raised Garden

Healthy scallion in raised bed.

An onion set is a third way to plant onions. When you have onion sets, these are small bulbs that measure around an inch in diameter. Onion sets include shallots. According to Grow Veg, it is easy to use shallots to replant a crop of onions.  

As previously noted, the added bonus is you get more than one onion per onion when you replant scallions. Grow Veg adds, “Whereas onions produce just one bulb per planted set (immature bulb), shallots commonly produce anywhere between four and 12 bulbs per set.”

To plant onion sets, you work with these like they are seeds. Each bulb should be planted about one inch deep in the soil in the spring or fall. When the onion sets grow a shoot, these can be harvested as chives or scallions, depending on the variety. Continue growing for 90 to 120 days, which is three to six months, to achieve the size of a full-sized round onion.

How Deep Should a Raised Bed be for Onions?

Since the root system of an onion is only a few inches long at most, and it does not get complex, you can use very shallow raised beds for onions.

Watering Onions in Raised Beds

A major threat to onions of any variety is water. Too much water is going to create a horrible living environment for these short-rooted plants. Also, the bulb of the onion and the shoots are layered, which creates a hiding space for mites and other pests.

Over-watering creates a habitat for these along with mold and mildew. Only water onions in raised beds every week or so as needed when the top layer is dry. As the onions grow larger, they will benefit from the regular use of fertilizer and soil supplements to boost nutrients, which help protect the developing bulb. 

Recap FAQ’s

Can you grow onions from just an onion?

Yes you can and quite easily when using a green onion. If you want to grow an onion from a white, yellow, or red onion, such as the famous Vidalia onion, you can replant this kind, as well. 

How do you grow onions from cutting onions?

Cut scallion in jar with water.

If you are using green onions, you simply use the white root end of the long green tube of the onion for replanting. Stick this end in some water in a small jar, and leave on the windowsill. To replant a round onion, start by chopping off the onion where the bottom of the onion is located.

How long do onions take to grow?

This will get you a new sprout of green onions in just a few days and you will double your initial investment in green onions from the market. For large, round onions, it takes approximately 90 to 120 days to grow an onion this way. 

How many onions can you grow from one onion?

You can regrow a long, green onion for about two weeks before it starts to lose its potency and can no longer stand up on its own. When this happens, the green onion becomes white and the roots start to interlock. There may even be a film and black mold starting to grow on the roots in the water. You want to toss the green onion root stem at this time, as you cannot continue to regrow it.

For a round onion, you can only grow a single new onion from an old onion bottom. However, there is an exception to the rule. If you want to grow more than one onion from a single onion end, choose the mighty and oval shallot. You can grow up to a dozen shallots from a single shallot shoot in a raised garden bed.