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Best Ways to Plant Onion Bulbs And Sets

One of the Most Beloved Foundational Crops in Any Garden is the Onion

Most of us use them in hundreds of dishes throughout the year, and widely consider them a kitchen staple. As spring approaches and we begin to dream about our gardens, most of us don’t really consider the onion a daydream-worthy crop.

Planting onions may seem almost secondary in thought, but the reality is, there is a lot to be considered in order to have a bumper crop of this centuries-old mainstay.

close up of onion bulb in the soil in the vegetable garden

Ensuring Onion Growing Success

Learning how to grow onions successfully depends on a number of factors, actually. Taking into consideration your planting region, average climate, garden placement (are you planting in containers, raised beds or open fields), and certainly varietals, are all part of the process. Depending on your planting region, onions will thrive at different points in the year.

If you are unsure which zone you are in, consult a hardiness zone map to find your planting zone.

Planting onions in colder regions (typically zones 1 -5) should occur as soon as the ground is able to be worked up. During a normal year, this is often late April to mid-May. Bear in mind, as gardeners, we are subject to the whims and fancies of Mother Nature. Some years you may have an early thaw. While onions are hardy and will survive a secondary freeze, it is always better to proceed with caution and exercise patience. If you live in a warmer region (zones 6-13) onions are able to effectively be planted year-round, however, extreme heat can compromise an onion crop.

Onion Seeds vs. Onion Sets

While considering how to plant onions, your first decision will likely be whether to start with seeds or sets. Onion sets can be planted without having to worry about frost damage. As a frost-hardy plant, onion sets have a much higher success rate than starting with seeds. The exception to this would be starting your onion seeds indoors.

How To Grow Onions from Seeds

If you have the space and desire, starting onions from seeds indoors is not difficult, it simply adds an average of two months to your planting process. Starting with an indoor container approximately 4 to 6 inches deep (your width and length will depend on the amount of seeds you would like to start), fill the container almost entirely to the top with a quality organic seed starter soil. Sow the seeds ¼ inch deep in even rows and cover lightly. Keep the soil moist and warm, and within a couple of weeks, you should begin to see green shoots emerge.

gloved hands planting red onion in garden

Starter Greens

There are two schools of thought on the starter greens. Some people clip the greens in order to manage plant size, others argue this is an unnecessary step. The number one rule of gardening is that experimentation will yield different results for every individual gardener. A particular step that may work well for you, may not work at all for another.

Ultimately, clipping the greens will not kill off your starter seeds, so if it is a step you feel is necessary, go for it. If you feel it isn’t necessary or don’t have the time, that is perfectly okay as well.

Within 6 weeks, your indoor plants will be ready for transplanting outdoors.

Transplanting Seedlings Outdoors

To transplant your seedlings, group them in bunches of 3 or 4 and place them in fertile, well drained soil 4-5 inches apart, leaving greens above the dirt. Contrary to transplanting seedlings, planting onion sets is a more simple process.

Planting Onion Sets

Make sure you have a section of your garden, whether it is a raised bed or field, that is sunny and not shaded by other plantings (onions love sun!). Onions will thrive in fertile, well-drained soil and will thrive further with a quality organic nitrogen rich fertilizer applied during planting.

Plant onion sets 4 to 5 inches apart in rows 12-18 inches apart and no more than one inch below the soil. Once planted, onions typically develop into full-sized bulbs after 3 to 4 months.

As is important throughout your garden, keeping onion rows free from weeds and pests is vital to their success. Onions need a lot of nourishment and feed from the soil constantly, so if they are competing with surrounding weeds, they will suffer. Additionally, lightly working up the soil between rows will help to keep the soil not only weed free, but also well-drained.

When to Harvest Onions

Onions should be harvested in late summer, prior to the onset of cool weather to prevent spoilage or damage from the direct sun. Bulb onions should be harvested approximately 100 to 125 days after planting. Unlike the green onions, bulb onions will communicate with you and let you know when they are ready for picking.

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woman harvest green onion in vegetable garden

Pest Deterrent

Onions in and of themselves are natural pest repellents and are not as prone to pests as many other plants. However, onion companion plants can not only help with pests but also create a mutually beneficial growing environment for onions and their companions. If you do notice some pesky creatures infiltrating your onion crop, a simple homemade onion and garlic “tea” sprayed on the crop will help deter further infestation. Simply liquify one onion and one garlic bulb in a blender and add water enough to make it a consistency that is able to work in a standard spray bottle and apply as necessary.

Tip: This concoction works well throughout the garden!

Harvesting Onions

Knowing when to harvest onions will yield the best flavor and quality. After 3-4 months, as the onions come to maturity, don’t feel pressured to harvest your entire crop immediately. Onions will continue to do well for a few weeks post-maturity. Their growth slows and they remain vital in the soil for several days/weeks. However, if you notice they are beginning to soften, it is time to pull them. Onions are easy to store throughout the winter, whether chopped and frozen or braided and hung to dry, just remember that when the next season comes around, rotating your onion crop is the final step to successful onions.

Make sure you take note of the location from the previous year so that you don’t replant in the same location two years in a row. Enjoy all of the versatility this staple has to offer.

Start harvesting onions today and get everything you need from Kellogg Garden at a store near you today!

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  1. I have a question about soil. I plant predominantly in elevated beds and containers. At the end of the season I dave the soils in large barrels and reuse the next year after mixing w fresh compost and fertilizers. I keep my tomatoe soil separate so I don’t plant tomatothat again. again. What I am struggling with is how to use soil from my garlic and onion planting? Should I mix it in with the rest? Any thoughts are appreciated.

    • Hi Murphy, we’re glad you asked; crop rotation is an excellent method to practice. The good news is that garlic and onions are light feeders. So, after harvesting your onion or garlic, you may want to plant some heavy feeders in this soil, such as; Broccoli, Brussel sprouts, kale, cauliflower, Kohlrabi, radishes, or turnips. Of course, it never hurts to amend the soil some more before planting, and you can get more tips on amending your soil here Let us know if you have any more questions, we’re happy to help!

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