When to Plant Onions in Missouri for a Good Harvest

Written by

William Golder


Dorian Goodwin

when to plant onions in missouri

When to plant onions in Missouri is a popular concern for many gardeners in the midwestern state. Understandably, onions are sought after for their amazing, pungent flavor and minimal space requirements.

If you’re planning a new crop of this vegetable, the growing season for onions is as follows:

  1. March 10 to 30 in southern Missouri, March 15 to April 15 in central parts of the state, and March 25 to April 15 in northern MO.
  2. Alternatively, plant onions in September and October for fall harvest, though note that timing variations exist depending on your first frost.

Best Time to Plant Onions in Missouri

1. In the spring, around March and April


Gardeners can select from seeds and transplants in addition to sets or bulbs when growing onions in Missouri.

However, it’s vital to note that seeds take longer to mature than the other mediums, though they are useful for growing rare cultivars and gardening on a budget.

Regardless of which type you choose, successful planting is achievable if you adhere to the following guidelines:

  1. Plant onion bulbs and transplants four weeks before the last frost in spring. In practice, sow them outdoors when the ground is workable and a hard freeze measuring 28 degrees Fahrenheit is unlikely. There’s no need to grow them inside your home first.
  2. In case you opt for seeds instead, start them indoor in pots eight to ten weeks before the final frost. Avoid direct sowing outside to give onions more time to establish before summer arrives.

The seedlings will be transplantable once eight weeks have passed and the ground is workable.

Because Missouri spans hardiness zone 5 to 7, we have the approximate planting dates below.

Hardiness zone Average last frost Plant outdoors (bulbs and transplants) Plant indoors (seeds/8 weeks before the last frost)
5 April 7 March 10 February 11
6 April 1 March 4 February 5
7 March 22 February 23 January 26

2. In the fall, around September and October


Another onion growing time is in the fall. If you pick this season, make sure to plant crops when the ground measures 50 to 68℉.

Either seeds, sets, or transplants may be used, with the following guidelines guaranteed to produce good results:

  1. Plant onion in soil eight weeks before the first frost if using seeds and six weeks before said date if using transplants.
  2. The six-week guideline also applies to sets, though these are more often grown in the spring rather than fall.

Considering that Missouri has its first frost around October 8 to October 15 in northern and central parts of the state, growers can plant seeds here around August 13 to August 20.

Meanwhile, individuals in the Southeastern Lowlands will see better results with a September 3 to September 6 planting, since this region welcomes its first frost around October 29 to November 1.

Due to the disparities in frost dates, it’s better to do your own calculation while determining your seeding schedule.

Tips for Successful Onions Planting in Missouri

1. Pick cultivars that suit Missouri’s climat


The best onions to grow in MO are long-day varieties. Day-neutral types can also do well here, particularly in central parts of the state.

On the other hand, it’s wise to avoid planting short day onion if you don’t live in zone 7 or south of Missouri.

Some types of onions to grow are: Candy, Yellow Sweet Spanish, Texas Supersweet, White Sweet Spanish, and Beltsville Bunching.

Additionally, refer to the best time to plant vegetables in Missouri, such as Tomatoes, Pumpkins, and Strawberries,…

2. Prepare the soil before sowing


Onions growing conditions include loose soil with a pH of 6 to 7. A spot with full sunlight and an inch of compost will help plants absorb water and other nutrients while suppressing weeds.

It is also ideal to test the soil before planting to get the best fertilizer recommendations. Low-nitrogen formulas like a 5-10-10 will encourage bulb formation well.

3. Follow the correct planting depth and spacing


Here are the depths and spacing onions need to thrive:

  1. Sets – 1 inch deep, 4 inches apart
  2. Seeds – 1/4 inch deep, 1 inch apart
  3. Transplants – same as sets

Overall, give onions adequate clearance to improve air circulation and keep them from competing with each other.

Water the soil thoroughly after planting with an inch of water per square foot per week. Cover the onions with mulch in the winter to protect them from cold damage.


The time to harvest mature onion is late summer and fall if you grow onion bulbs. For those who like eating scallions, harvest time will come much earlier in late spring, provided the guidelines on when to plant onions in Missouri are followed.

If you have any more questions on this topic, feel free to leave us a message. Thank you for reading.

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