Onions are the quintessential storage crop and the backbone of most recipes. A must have for any vegetable gardener, it pays to learn how to grow your own onions. Enjoy our Onion & Leek Planting Guide for information from planting to harvesting & curing.
Keene Garlic is happy to offer both Certified Organic Onion/Shallot/Leek Plants as well as Naturally Grown Onion Sets for spring planting.
Our Certified Organic Onion & Leek Plants are greenhouse-grown on small, family farms in Wisconsin. These live seedlings arrive in a container with soil, hardened off, and ready to plant. Our local organic onion growers prefer these onion starts because they are easy to grow with high yields. Naturally Grown Onion Set Sampler
Our naturally grown onion sets will arrive in a netted bag. Plant these small bulbs whole in spring for a summer bounty. They come in Red, White or Yellow, or order our NEW Onion Set Sampler. Upon arrival, unpack your onion sets from the box and store in a cool, dry place until it is time to plant.
Onion transplants provide a convenient way to get a head start on growing big, beautiful onions. By skipping the indoor seed starting stage, you can go directly to planting outside at just the right time With proper planting techniques, your onion transplants will flourish and reward you with a plentiful harvest
When is the Best Time to Plant?
Timing is critical when it comes to planting onion transplants. Onions are cold hardy but the tender young transplants need time to establish roots before hot summer weather arrives. The ideal window for planting is 4-6 weeks before your expected last spring frost date. Plant too early while soil is still cold and you risk shocking the transplants. Plant too late after warm weather has already set in and growth may be stunted. Check with your local agricultural extension service for frost dates specific to your growing region.
Prepare the Planting Area
Onions prefer nutrient-rich, well-draining soil for optimal growth Test your soil and amend as needed to reach the ideal pH range of 6.2-6.8 Onions thrive in slightly acidic to neutral soil. Spread compost, peat moss, vermiculite or other organic matter to improve drainage and nutrient content if needed.
Before planting, work 1-2 inches of compost or a balanced fertilizer such as 10-10-10 into the top few inches of soil. Onions are heavy feeders and need nutrients right from the start. You can also use a fertilizer with a slightly higher phosphorus middle number to encourage root growth in young transplants.
How Deep and Far Apart?
Proper planting depth and spacing ensures your transplants have sufficient room to size up properly Onion transplants should be planted 1 inch deep with just the bottom portion buried Planting too deeply can inhibit bulb formation.
Space the transplants 4 inches apart if growing to full maturity. You can also plant closer at 2 inch spacing and harvest some onions early as green onions. Wider 6 inch spacing may be needed for larger varieties.
Allow 16-18 inches between rows or beds. Onions don’t like competition so make sure not to overcrowd.
Should You Plant in Trenches?
Planting in raised beds or trenches improves drainage and nutrient absorption. Dig trenches 4 inches deep and 4-6 inches wide. Sprinkle 1⁄2 cup balanced fertilizer per 10 feet of row length into the bottom of the trench. Cover with 2 inches of soil before planting transplants along the sides.
Leave a buffer between transplants and trench edges to prevent washout when watering. Raised beds also elevate the onion roots above compacted soil.
Follow Proper Planting Techniques
Carefully separate each onion transplant, keeping the roots intact. Plant them upright at the recommended 1 inch depth, firming the soil around the roots to remove air pockets.
After planting, water the transplants thoroughly to soak the root zone. Continue daily watering for the first week if rainfall is lacking. Newly planted transplants need consistent moisture to reduce transplant shock.
Provide Proper Care
Weed weekly to prevent competition, especially when plants are young. Side dress with a nitrogen fertilizer 4-6 weeks after planting when plants are 6-12 inches tall.
Onions have shallow roots so maintain consistent soil moisture of 1-2 inches per week through watering. Mulch after planting to retain moisture and reduce weeds. Take prompt action if pests like onion thrips are detected.
Harvest at the Right Time
Onions tops will fall over and turn brown when mature. Use care when harvesting to avoid bruising bulbs. Allow onions to cure for 1-2 weeks in a warm, dry spot before trimming roots and stems for storage. Cured properly, homegrown onions will last for months.
With the right planting methods and attentive care, your onion transplants will flourish and provide a bountiful harvest. Pay close attention to details like planting depth, spacing, soil preparation and consistent watering. Then enjoy their sweet ripe flavor.
Troubleshooting Common Problems
Even when planted correctly, onions can sometimes encounter issues. Here are solutions to some common transplant problems:
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Leggy or falling over – Onion seedlings started too early indoors before planting can become leggy and fall over more easily. Use a fan to strengthen stems. Plant a little deeper or support with stakes if needed.
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Not bulb swelling – Onions require long summer daylight hours to properly form bulbs. Start transplants indoors no more than 10-12 weeks before your last expected spring frost.
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Flowering – Some varieties bolt quickly in hot weather. Choose early-maturing, heat-tolerant varieties less prone to premature flowering.
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Misshapen or double bulbs – Overcrowded plants compete for nutrients resulting in deformed bulbs. Allow proper spacing between transplants.
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Stunted plants – Factors like poor drainage, pests, diseases or nutritional deficiencies can inhibit growth. Improve conditions and remedy any issues promptly.
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Rotting bulbs – Excess moisture leads to bacteria and fungi that cause bulbs to rot. Allow soil to dry adequately between waterings and avoid waterlogged conditions.
Catch problems early and take quick action to get plants back on track. Keeping transplants healthy means more onions to enjoy.
Key Tips for Onion Transplant Success
Follow these best practices when planting onion transplants for the highest yields:
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Prepare soil 2-3 weeks before planting and amend to ideal onion conditions.
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Time planting 4-6 weeks before expected last spring frost.
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Space transplants appropriately based on variety and maturity required.
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Plant at proper 1 inch depth in trenches or raised beds.
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Water newly planted transplants daily if rainfall is insufficient.
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Weed diligently and fertilize 4-6 weeks after planting.
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Maintain even soil moisture of 1-2 inches weekly.
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Control pests immediately and harvest promptly when mature.
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Cure harvested onions well before storing for winter.
Paying close attention to timing, spacing, soil, moisture and pest control will get your onion transplants off to a vigorous start. Adopt these planting best practices for a bountiful harvest of sweet, juicy onions.
Basic Onion & Leek Growing Info
- Sun Requirement & Timing: Onions require full sun – the more the better! Therefore, avoid planting next to crops that might shade your onions. It is typical to plant onions as early as 4 to 6 weeks before the last estimated spring frost.
- Soil Preparation: Alliums need full sun & loose, nutrient rich soil. Proper drainage is also key to growing great onions. Adding compost or a well-balanced organic fertilizer to the soil prior to planting is recommended, especially if your soil fertility is low. Our Keene Garlic Fertilizer is great for all alliums! If you have heavy soil, it is recommended to plant them in raised beds or raised bed rows at least 4″ high to promote sufficient drainage.
Plant onions close to the surface, making sure the roots are fully covered. It is best to plant into damp soil and water shortly after planting. There are a couple of good ways to plant onions:
Option #1: Plant single onion plants 4” apart in rows that are 10-12” apart. Recommended.
Option #2: Plant groups of 3 onion plants 10” apart in rows that are 10-12” apart. This allows for all 3 onions to spread out and grow to full size. This method allows for easier weeding between plants when they are small.
- Plant leeks individually in a 6 inch deep trench. Fully cover roots at planting time.
- As leeks grow, add more soil every week or two to promote long, white stalks.
Alliums have shallow root systems and do best with about 1 inch of water per week, especially during bulbing time. Alliums do not compete well with weeds so it is important to keep weed pressure down for optimum growth.
It is recommended that you add a specialty fertilizer such as Keene Garlic’s Garlic Fertilizer (made for all alliums!) or an All-Purpose Fertilizer to the soil at the time of planting. You may reapply every 10-14 days until bulbing starts. Keene Garlic Fertilizer 5-2-2-1
This Transplanting Method for Onions Is a GAME CHANGER
FAQ
How to plant onion slips in the ground?
- Timing: Plant onion slips in early spring, once the ground is workable and the danger of frost has passed.
- Location: Choose a sunny spot with at least 6 hours of sunlight per day.
- Soil: Onions prefer fertile, well-drained soil with a pH between 6.0 and 6.8.
- Improve Soil: Amend the soil with compost or other organic matter to improve drainage and fertility.
How do you manage onions after transplanting?
After transplanting seedlings they should be watered daily until the plants stand up. Onion roots can penetrate up to 800mm but most roots feed in the top 200mm – 300mm of soil.
What should not be planted near onions?
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Peas and Beans:Onions and beans, especially bush beans, don’t grow well together because onions can stunt the growth of beans.
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Asparagus:Onions can inhibit the growth of asparagus by competing for nutrients and potentially introducing pests that target both plants.
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Sage:Sage releases chemicals that can hinder onion growth, making them incompatible companions.
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Fennel:Fennel has allelopathic properties that can inhibit the growth of onions, and they also compete for nutrients and space.
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Cabbage Family:While onions can help deter pests that target cabbage family plants, avoid planting onions near cabbage family plants as onions may compete for nutrients and space.
Can onions be transplanted?
Onions can be direct-seeded, transplanted with field-grown or greenhouse-grown transplants, or planted using onion sets, and onions are planted on flat-ground and raised beds (Figure 1). The between-row and within-row plant spacings vary considerably depending on the region, soil type, type of onion, and target market.
When should you transplant onions?
Onions are perfect to start in cool weather and can take a light frost. Transplant your onions during the early spring when it starts to warm-up outside and there is no more danger of frost. Did you know that transplanting onions is actually pretty easy? Growing onions is a simple process, plus you need to start the onion seeds indoors!
Can I transplant green onion seedlings?
If you do want to transplant green onion seedlings, plan to sow them indoors around four weeks before you aim to plant them outdoors. Just like bulb onions, they can be sown either in trays or modules, but should be planted just 6 inches apart when transplanted out in the vegetable garden or container.