How to Trim Onion Plants


Boost the flavor of your favorite dinner dish with onions, a pungent and sweet herb that grows a large and juicy bulb underground. Encourage the underground bulb growth by keeping the onion's foliage trimmed. This helps divert the plant's energy and nutrients toward bulb development rather than growing large leaves or flowers. Trim regularly throughout the onion plant's lifetime until harvesting.

Step 1

Set a ruler in a vertical position against the onion with one end resting on the base of the onion where the plant enters the soil.

Step 2

Measure 4 inches from the onion's base and mentally mark where this is on the plant.

Step 3

Grasp the onion leaves together. Use sharp scissors and trim the onion plant at the 4-inch mark. Discard the cut leaves or throw them into your compost pile.

Step 4

Repeat the trimming process as needed to keep the onion plants at a height of 4 inches until harvesting. Onions are ripe and ready for harvest when 25 to 50 percent of its tops have wilted and the onion bulbs have grown a paperesque skin.

Things You'll Need

  • Ruler
  • Scissors


  • "American Horticultural Society: A to Z Encyclopedia of Garden Plants"; Christopher Brickell; 2004
  • "The Complete Book of Herbs: A Practical Guide to Growing and Using Herbs"; Lelsey Bremness; 1994

Who Can Help

  • University of Illinois: How to Grow Onions
Keywords: trim onion plant, grow onions, prune onions

About this Author

Josh Duvauchelle is an editor and journalist with more than 10 years' experience. His work has appeared in various magazines, including "Honolulu Magazine," which has more paid subscribers than any other magazine in Hawaii. He graduated with honors from Trinity Western University, holding a Bachelor of Arts in professional communications, and earned a certificate in applied leadership and public affairs from the Laurentian Leadership Centre.