How to Plant Onion Transplants for a Successful Crop

Planting onions using seedlings is the only way to go in my humble opinion. Let’s talk about why!

Onion transplants are a great way to get a head start on growing big, healthy onions. Buying transplants instead of seeds allows you to skip the indoor growing stage and go straight to planting outside. With the right planting techniques, your onion transplants can thrive and produce a bountiful harvest.

When to Plant Onion Transplants

Timing is crucial when planting onion transplants, Onions are cold hardy but transplants need time to establish roots before hot summer weather arrives, The ideal window for planting is 4-6 weeks before your last expected spring frost Plant too early and the cold soil will shock the transplants Plant too late and the heat will stunt their growth, Check with your local agricultural extension service for frost dates specific to your region,

Preparing Your Soil

Onions need nutrient-rich, well-draining soil to grow their best. Amend your soil with compost or other organic matter to improve drainage and nutrient content. Onions prefer a soil pH between 6.2-6.8. Test your soil pH and add lime to raise the pH or sulfur to lower it as needed.

Work the fertilizer into the top few inches of soil before planting. Choose a balanced fertilizer with an NPK ratio like 10-10-10 or one with a slightly higher phosphorus level.

Planting Depth and Spacing

Proper planting depth and spacing ensures your onions have enough room to size up Onion transplants should be planted 1 inch deep with just the bottom portion buried Planting too deeply can inhibit bulbing,

Space the transplants 4 inches apart if growing to maturity. You can plant closer, 2 inches apart, if harvesting some as green onions.

Allow 16 inches between beds with 36 inches between fertilizer trenches. Avoid overcrowding to prevent competition for nutrients.

Planting in Trenches

Planting in trenches or raised beds improves drainage and nutrient absorption. Dig trenches 4 inches deep and 4 inches wide. Sprinkle 1⁄2 cup fertilizer per 10 feet of row length and cover with 2 inches of soil before planting transplants.

Plant the onions along the sides of the trench, not in the bottom. Leaving a 2 inch buffer between transplants and trench edges prevents washout.

Proper Planting Techniques

Handle transplants gently when planting to avoid damaging the roots. Carefully separate each plant and plant upright at the recommended depth. Firm the soil around each transplant to remove air pockets.

Water transplants immediately after planting and daily for the first week if rainfall is insufficient. Soak the soil thoroughly without washing out the plants.

Ongoing Care

Weed weekly to prevent competition. Apply a side dressing of nitrogen fertilizer like ammonium nitrate 4-6 weeks after planting when plants are 6-12 inches tall.

Provide 1-2 inches of water per week by rainfall or irrigation. Onions have shallow roots and need consistent moisture. Mulch around plants to maintain soil moisture and reduce weeds.

Be prepared to take measures to thwart pests like onion thrips which can damage developing bulbs. Make sure to harvest onions promptly once the tops fall over and dry. Curing harvested onions properly maximizes storage life.

With the right planting techniques and care, your onion transplants will reward you with bountiful, picture-perfect bulbs. Pay close attention to proper planting depth, spacing, soil preparation and consistent moisture. in no time you’ll be enjoying homegrown onions bursting with fresh flavor.

Troubleshooting Common Onion Transplant Problems

Even when planted properly, onion transplants can still run into issues. Here are some common problems and how to remedy them:

Leggy or falling over: Transplants started too early indoors can become leggy and fall over after planting. Use a fan indoors to strengthen stems. Plant a little deeper or support with stakes.

Not bulb swelling: Bulbing requires long daylight. Start transplants indoors no more than 10-12 weeks before your last spring frost date.

** Flowering:** Some varieties bolt quickly in hot weather. Plant early-maturing, heat-tolerant varieties.

Misshapen/double bulbs: Overcrowding leads to abnormal bulbs. Allow proper spacing between plants.

Stunted plants: Compacted soil, overwatering, pests, diseases, or nutrient deficiencies can stunt growth. Improve drainage, avoid overwatering, and remedy any pest/disease issues.

Rotting bulbs: Excess moisture leads to bacterial soft rot. Allow soil to dry between waterings. Avoid waterlogging.

Pay close attention after planting to spot any issues early. Taking prompt action can help minimize transplant shock and keep your crop thriving.

Best Practices for Onion Transplant Success

Follow these best practices when planting onion transplants for optimal growth and yield:

  • Test and amend soil to onion preferences well before planting.

  • Time planting 4-6 weeks before last spring frost.

  • Plant in trenches/raised beds to improve drainage.

  • Allow proper spacing between transplants.

  • Plant 1 inch deep, tops just above soil surface.

  • Water newly planted transplants daily if rainfall is lacking.

  • Weed weekly to prevent competition for nutrients.

  • Side dress with nitrogen fertilizer 4-6 weeks after planting.

  • Maintain consistent soil moisture of 1-2 inches per week.

  • Take action immediately if pests like thrips found on plants.

  • Harvest promptly once tops fall over and cure bulbs well.

Follow these tips and you’ll gain a better understanding of how to plant onion transplants successfully. Pay close attention to details like spacing, planting depth, and consistent watering when planting. Then provide proper care throughout the growing season. With this knowledge, you’ll be harvesting an abundance of juicy, flavor-packed onions.

Planting onions by Sets

Onion sets are partially grown onions. They are usually no larger than an inch or so. When planted just below the ground in early spring, these sets sprout and grow into full-grown onion bulbs. Many folks plant onions this way and have great success. I planted onions this way for the first ten years we had a garden, and we always got a good crop.

The problem with onion sets is that the sets are actually in their second year. Onions are biennial plants, which means they sprout and grow a bulb in their first year. These bulbs will grow again the next year if they are not picked the first year. They will send up a flower stalk and make seeds.

The problem with sets is the plants “think” they are in the second year if planted by set. You have a lot more problems with flower stalks, and the bulbs never get as big because the plants are too busy making flowers and seeds.

Don’t get me wrong, a lot of people are great at growing onions from sets. But if you plant them this way, you won’t get bigger onions that last longer.

Third, you can buy them directly from the growers, online!

This has been the best method for me. The grower that I buy from (Dixondale Farms) harvests and packs the seedlings right in the field and then ships them out to me. They arrived less than a week from being harvested and I can put them right back into the ground in my garden!

Also, they know exactly when to plant them in my area, so they are sent to me at the exact time I should be planting!! Many growers offer BIG discounts for bulk orders, so call up your neighbors or a gardening club and buy a lot at once. That often will get the price below $3. 50 for a bundle of 60 plants!.

This Transplanting Method for Onions Is a GAME CHANGER


How deep do you plant onion transplants?

Plant the onions 1″ deep and no deeper, as this will inhibit their ability to bulb.

Do onions transplant well?

Onions can be grown successfully from seed, sets or transplants. Deciding which method to use depends mainly on personal preference. Variety of choice has a much bigger impact on harvest than which propagation method is chosen.

How big should onion seedlings be before transplanting?

When onion greens are 5 to 6 inches tall, it’s time to transplant them into individual cells. Begin by carefully overturning the seedlings onto your hand. Gently separate the roots of the seedlings from each other, holding each seedling by the green tops.

Can onions be transplanted?

You can transplant onions from existing onion plants or buy bareroot onion bundles for transplant. You can even start the seeds indoors to be transplanted later. For those in the northern US: You will be starting onions at least 8 weeks before the last frost of winter.

How do you plant an onion plant?

Prepare the planting bed by adding fertilizer as described above. Amend soils as needed with well-composted organic matter. Planting in mounded rows helps improve drainage in heavy soils. Plant transplants or onion sets 1 to 1½ inches deep in rows 12 to 18 inches apart. Space transplants 4 inches apart within the rows.

How do you transplant onion seedlings?

Onions also need the soil to be loose. Compact soil inhibits bulb development. So, be sure to vigorously till the planting bed. If you have a lot of clay in your soil, you can augment it with sand or vermiculite. Traditionally transplanting onion seedlings involved a special tapered tool known as a dibbler.

How far apart should onion transplants be planted?

When planting onion transplants into several rows of onions, leave 16″ between the outside edge of one bed, and the outside edge of the next. The spacing from the center of one fertilizer trench to the center of the next should be 36″.

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