Fertilizing Onions

When onions grow to 6″ and again at 12″ tall, it is time to fertilize them. Avoid fertilizing within a month of harvesting.

square foot gardening onions 6 inches Here’s a picture of my onions at 6″ tall

Application Rates

Traditional gardens

Apply 1/2 pound (or 1 1/4 cups) of 21-0-0 (Ammonium Sulfate) to 100 square feet

Square Foot gardens

Apply 1/2 cup of 21-0-0 (Ammonium Sulfate) to 12 squares

square foot gardening onions fertilizer My onions after applying 21-0-0 fertilizer

Organic Alternatives

Apply blood meal or soybean meal.

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5 Responses

  1. Donna Bentkowski says:

    I was told my Dixondale Farms,famous for growing onions, to fertilize my onions very 2 wks with blood meal along with Medina Hasta grow and Medina growing Green very other month.this person who i spoke to has been growing onions for 35 yrs.

  2. Emily says:

    Leeks are very similar to onions, especially when it comes to fertilizing. Follow this link to see their needs. Garlic grows from fall to spring, and needs fertilizer at planting and then again in the spring (21-0-0).

  3. Digitoes says:

    Do we also apply fertilizer to garlic, shallots and leeks?

  4. Emily says:

    It depends on the type of fertilizer. The 21-0-0 I used (ammonium sulfate) I just sprinkled on the squares with onions. But some fertilizers are made to mix with water, and apply as part of watering the plants.

  5. How do you apply it? Do you just sprinkle it on over the soil or does it need to be worked in somehow?
    This year is my first time ever growing onions.