How Deep To Plant Onion Sets – An In-Depth Look

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Last Updated on January 26, 2022 by Fabiola L.

One of the most loved crops in any garden is the onion being used in hundreds of dishes in any kitchen; but how deep do you plant onion sets.

Spring is the season we all start dreaming of going back to our gardens and growing some vegetables or flowers.

Onions are among the many crops that gardeners chose to grow. Successful onion gardening depends on several factors that include,

  • Your planting region
  • The average climate
  • Garden placement
  • The onion variety

Depending on your region, onions will thrive at different times of the year.

Onion Sets Vs. Onion Seeds

When you are considering growing onions, you will have to choose whether to start with seeds or sets.  Onion sets can be planted even in the cold season without worrying about frost damage.  They are frost-hardy and have a higher success rate than the seeds.

For onion seeds, you can start them indoors to ensure they germinate properly and then transplant them outdoors.

Onion Sets Vs. Onion Seeds

When To Plant Onion Sets

Starting from March onwards, the onion sets are available for sale and ready to grow.  Onions store very well and there is no need to plant them staggered over a period.

The best plan is to plant your onion sets together at one time.

If you do prefer to plant your onions sets under the protection of cloches then plant them two weeks earlier than the above date. Choose a day when the soil is not waterlogged.

Read more about How Far Apart to Plant Potatoes

How To Plant Onion Sets

Onion sets are easy to grow on all types of soils but they prefer a well-dug soil, a few months before planting.  They thrive in well-drained soils that are neither alkaline nor acidic that are well moisturized.

Onion sets also prefer a location with full sun or at least partial sun. Ensure you practice good crop rotation to keep them from getting affected by diseases.

Grow them where no onion family – leeks, spring onions, garlic, onions, have grown in the recent past at least 2 to 3 years.

How Far Apart To Plant Onion Sets

Planting onion sets is simple and fast but you must know how far apart to grow them.  Onion plant spacing is important in ensuring your plants are set in the right space to thrive.

To ensure you get the measurements right, first mark out the row with a string bamboo cane or string to keep the row straight.

Your Plantings row should be about 30cm apart enough to allow you space for weeding.  Cover them with soil up to the root end onto the soil and tassel end.  Once you cover with soil, gently firm the soil down and Scatter some fertilizer – bonemeal or blood fish around the soil around and work it into the surface with a trowel.

Check out the Top Best Soil Test Kit You Can Invest In

How Deep To Plant Onion Sets

Once you have marked the measurements for rows and holes it’s time to make holes now.

Make a hole in the soil with your finger at least 5-10cm or more depending on the size of the onion sets, and place them into it.  Making a little hole for each onion set will keep you from damaging the roots rather than just forcing them into the ground.

For the first few weeks after planting, the birds will be a huge problem for your onion sets.  To avoid this destruction, spread some gardening fleece over the soil surface.  Secure it down with stones or soil. You can remove the fleece after a month.

How Deep To Plant Onion Sets

If you want to grow larger onions, you can start your sets either in a greenhouse or indoors.   Place the onion sets into germination trays filled with multi-purpose compost a few weeks earlier than normal.

They will quickly grow roots and sprout shoots. Transplant them outdoors at the same time as you would plant unsprouted onion sets.

Find more information about When Should Onions Be Planted?

Caring For Onion Sets

Onions are some of the easiest vegetables to grow.  They require very little attention too and they grow fast.  They have minimal foliage and require weeding throughout the growing season.

In the dry weather, they will need plenty of water more than the normal season. If you have average, the soil you will need to feed it at planting with fish, blood, or bone fertilizer.  Do not feed it with nitrogen-rich fertilizer especially after July because it encourages thick necks and a high risk of neck rot.

Yelow Onion Sets (100 Bulbs) Garden Vegetable

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When the 3rd-week strikes, stop watering your onions even if the weather is hot and dry.  This is to encourage them to ripen and enable them to be stored for longer in the autumn and winter.

If you have the time in your hands for some gentle work, using your fingers, tease away some loose soil from the top of the onions to allow the top and neck receive as much sunshine as possible.

When To Harvest Your Onion Sets

Onion sets take about 90 – 120 days to mature.  The growing conditions throughout the spring and summer greatly affect the date your onions are ready for harvest.

Look for yellowing foliage and stems that are beginning to fall over as the key indicators for ready onions. Give your onions a period to dry in the sunny weather for about 2 to 3 days so that they can dry to increase their storage life.

Do not manipulate the foliage in an attempt to make the onions dry quicker. You will only be exposing them to the risk of neck rot.

When To Harvest Your Onion Sets

When you dig your onions, leave them on top of the soil to dry out for a couple of days. Should the weather turn damp, move the onions to a shed that has lots of ventilation.  Remove the loose soil and cut off the top foliage but you can leave some.  Finally, store your onions in a cool, dry place.


Onions are generally healthy vegetables but may suffer from pests and diseases though not in major cases.  These can be difficult to deal with and might require professional help to salvage your onions.

Overall, it is easy to grow onions from onion sets.  They grow much faster and give a good crop.  Why not try to grow your own when the season is right.

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