Should I soak onion plants before planting?

Onions are a popular vegetable grown in home gardens. When planting onion sets or transplants, a common question is whether the plants should be soaked before planting. Soaking onion plants can help in some circumstances but is not always necessary. Here is an in-depth look at the pros and cons of soaking onion plants before planting.

The Purpose of Soaking Onion Plants

The main reason to soak onion plants before planting is to hydrate them. Onion sets and transplants may dry out during storage and shipping. Soaking them in water before planting helps rehydrate the plants so they can establish a good root system after planting.

Soaking causes the onion plant to absorb water through its roots and tissues. This provides an immediate source of moisture to help the plant survive transplanting. It also “wakes up” dormant plants and gets growth started.

When Soaking May Help

Here are some specific situations when soaking onion plants before planting is recommended:

  • Using old onion sets – Onion sets that are not fresh may benefit from soaking.
  • Planting in hot, dry conditions – If transplanting when temperatures are very high and soil is dry, soaking plants provides an extra hydration boost.
  • Planting sets or transplants that appear shriveled – Shriveled or desiccated plants should be soaked to rehydrate tissues.
  • Growing sweet onion varieties – Sweet onions tend to be more sensitive to transplant stress, making soaking more beneficial.

In these situations, soaking in cool water for 2-6 hours before planting can help onion plants recover from storage conditions and establish better in the garden.

When Soaking May Not be Needed

Soaking is not always necessary when planting onions. Here are some cases when soaking onion plants is optional:

  • Using fresh onion sets – If sets are bright, firm and not dried out, pre-soaking is not really needed.
  • Planting in cool, moist soil – Soaking is less important if the planting area is already wet and temperatures are cool.
  • Transplanting onion seedlings – Young seedlings from seeds usually do not need soaking.
  • Planting green onion bunches – Grocery store green onions can be planted without soaking.

As long as onion plants appear hydrated and soil moisture is adequate, soaking may provide little extra benefit when planting.

How to Soak Onion Plants

If soaking onion plants before planting, follow these tips:

  • Use room temperature water – Avoid icy cold or hot water which could shock or damage plants.
  • Soak for 2-6 hours – A few hours is usually sufficient hydration time.
  • Don’t leave soaking more than 24 hours – Extended soaking can deplete oxygen levels and harm plants.
  • Separate and scatter plants – Spread out plants during soaking to fully hydrate each one.
  • Plant immediately after soaking – Get plants in the ground right after soaking to avoid re-drying.

You can soak onion plants in a bucket, sink, tub or other container. Change out the water once or twice during extended soaks to replenish oxygen. Drain plants well and transplant immediately for best results.

The Effects of Soaking Onion Plants

What does soaking actually do for onion plants? Here are some of the effects:

  • Rehydration – Soaking causes immediate absorption and replenishment of moisture.
  • Increased growth – Soaked plants will leaf out and root faster after transplanting.
  • Higher survival rate – Adequate moisture improves the odds of plants establishing successfully.
  • Bigger plants – Soaking sets often produces larger onions at maturity.
  • Faster maturity – Soaked plants tend to mature a little faster than non-soaked ones.

Research on onions confirmed that soaking sets significantly increased moisture content and fresh weights of transplants. However, the effects were most pronounced on old, dried sets vs. fresher ones.

Potential Problems with Soaking Onions

While soaking onion plants can be beneficial, there are a few potential downsides:

  • Extra time and effort – It takes time and labor to soak plants prior to planting.
  • Spreading diseases – Soaking can disperse diseases from infected to healthy plants.
  • Depleted oxygen – Long soaks may reduce oxygen levels in the water.
  • Too much hydration – Excessive soaking can lead to burst, swollen tissues.
  • Root damage – If not planted promptly, tender soaked roots may dry out again.

To avoid issues, soak plants in small batches, change the water periodically, and transplant immediately after soaking. Inspect plants closely and discard any that appear damaged or diseased.


Soaking onion sets or transplants before planting is recommended primarily when plants show signs of dehydration or when planting conditions are very hot and dry. For fresh, healthy plants being planted into properly prepared, moisture-retentive soil, soaking may provide only marginal benefits.

If you decide to soak onion plants prior to planting, allow 2-6 hours in cool, clean water. Monitor oxygen levels and discard any damaged plants. Transplant soaked sets immediately rather than letting them sit and dry out again. With proper technique, soaking onion plants can get them off to a vigorous start when breaking dormancy and becoming established in the garden.

Soaking onion plants before transplanting is an optional practice that can be beneficial but is not always necessary. Consider the condition of the plants and your soil moisture levels when deciding if pre-soaking is worthwhile. With a little extra care at planting time, you can give your onion crop its best possible start.

Frequently Asked Questions

How long should you soak onion sets before planting?

Most experts recommend soaking onion sets for 2-6 hours before planting. Longer soaking periods risk depleting oxygen levels in the water.

Should you soak onion transplants before planting?

Onion transplants may benefit from soaking, especially if the plants appear dried out or you are planting in hot, dry conditions.

Do you have to soak onion sets before planting?

Soaking is optional and not absolutely necessary in all cases. It can provide benefits when planting older or dried out sets.

What is the best water temperature for soaking onions before planting?

Room temperature water between 60-75°F is ideal. Avoid icy cold or hot water that could shock or damage the onion plants.

Should you soak green onions before planting?

Green onions purchased for planting can be soaked, but it is not essential. They contain a lot of moisture already.

Does soaking onion sets increase yield?

Research shows that soaking can increase bulb size and plant growth. However, effects are most noticeable on older, dried sets.

Can you soak onion sets too long before planting?

Yes, extended soaking beyond 24 hours can deplete oxygen levels and potentially harm plants. Stick to 2-6 hours.

Do you soak onion sets in warm or cold water?

Room temperature water is best. Avoid temperature extremes that could damage plants.

What happens if you don’t soak onion sets before planting?

Onion sets that are fresh may not need soaking. However, non-soaked plants may mature and establish a little slower.

Should you soak onions before planting in pots?

Yes, soaking can help when transplanting onions into containers, where soil moisture can dry out quickly.

Table Comparing Soaking Onion Plants vs. Not Soaking

Factor Soaking Onion Plants Not Soaking Onion Plants
Time and effort Requires 2-6 hours of soaking No extra time or work
Growth rate Typically faster growth after planting Slightly slower initial growth
Maturity rate Reaches maturity a little sooner May take a little longer to reach maturity
Bulb size Tends to produce bigger bulbs Potential for smaller bulbs
Transplant survival Higher survival rate of transplants Somewhat lower survival rate
Ideal conditions Recommended in hot, dry conditions Fine in cool, moist conditions

This table summarizes some of the potential differences between soaking and not soaking onion plants prior to planting. Effects tend to be most noticeable on older stored sets versus fresh plants.

The Bottom Line

Soaking onion plants before transplanting is a polarizing topic. Some gardeners swear by it, while others feel it is unnecessary. As with most gardening decisions, there are several factors to consider in determining if soaking your particular onion plants will be beneficial.

Old, dried out onion sets being planted into hot, dry soil would certainly benefit from hydration prior to transplant. Meanwhile, fresh onion seedlings being planted into cool, moist soil may do just fine without any soaking. Evaluate the condition of your plants and the planting conditions to make the call.

If in doubt, take the middle road and give your onions a brief 2-4 hour soak before planting. This provides a bit of insurance against transplant shock without requiring a major time investment. Pay close attention to your specific growing conditions, onion plant health, and maturity to make the right choice for each situation.

With proper techniques, soaking onions can help them establish quickly and grow vigorously. But take care not to overdo it. Moderation is key when it comes to this common but controversial gardening practice.

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