How to Plant Onions in Colorado

Onions grow well in Colorado.
Onions grow well in Colorado. (Image: Jupiterimages/ Images)

Onions grow well in Colorado when planted in the spring season. By avoiding excessively cold temperatures, you can maintain a healthy crop of these popular vegetables. Due to the favorable conditions for growing this crop, fresh onions are available in Colorado between July and September and locally grown onions from fall and winter storage can be found between August and April. Whether you’re interested in green onions or dry onions, you can use some simple planting methods to obtain a healthy crop.

Things You'll Need

  • Organic material
  • Soil till
  • Mulch

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Mix organic material into the soil at least 8 inches deep if your soil is heavy in clay or sand. Till all soil to this depth to avoid excessive compaction.

Spread a layer of organic material on the surface of the soil to a depth of about 1 1/2 inches.

Plant onion seeds or transplanted onion plants between the beginning of March and the middle of April. Space the plants evenly throughout the garden, between 3 and 4 inches apart. Seeds should be 1/2 inch to 1 inch deep in the soil.

Water thoroughly after planting and continue frequent watering to keep soil moist. Plants should be watered at least every five to seven days throughout the growing season.

Spread a layer of mulch around the onion plants to prevent weeds.

Tips & Warnings

  • Plant a cover crop in the area throughout the fall and winter to keep the soil from eroding.
  • Onion plants in Colorado can be successfully rotated with alfalfa, corn and other small grains.


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