Onion Planting & Care

Each year I talk to dozens of people about the size of their onions. Many cannot seem to get the large bulb onions like the one they get at the grocery store. As I talk to the customers there are three general mistakes made when planting their onions:

  • Planting depth
  • Space between plants
  • Fertilization

Let's start with planting depth.

Planting depth for onions is between 3/4″ and 1″. You can plant them a little deeper but be sure to pull the dirt back off of them after a good root system has taken hold. Many times onions do not form a bulb is because there is too much soil around the plant. To grow the largest bulbs pull nearly all the soil back from the bulb except for where the roots enter the ground.

Adequate spacing is also important.

If you are wanting green onions as well as bulb onions, space your plants at 3″ intervals, and pull every other plant when the time comes. However, I do not recommend this method because you generally pull the green onions when you are ready to eat them, and this may hinder your bulb onions from growing properly. What I recommend is planting your bulb onions at 6″ intervals to give them plenty of room to grow. If you want a 4-5″ diameter onion, you have to give it room. Then plant your green onions at 2″ intervals and pull them as you wish.

Finally, you need the proper fertilization.

Proper fertilization can make all the difference. Before planting, I recommend using 8-24-24. This blend gives you some nitrogen to get the plant started, but also gives you phosphorous for root development, and potash for root development, cold hardiness, and water efficiency. Put down about 2 lbs per 50′ of row and mix into the top few inches of dirt. This is where most people stop fertilizing, and that is a mistake. Onions require a large amount of nitrogen while growing. I recommend topdressing the onions with either 46-0-0 at 1/4 lbs per 50′ row or 8-24-24 at 1lbs per 50′ row. You will need to topdress the onions every 2 or 3 weeks until the stalk begins to get soft. This is usually about a month before harvest. Do not use a sulfate-based nitrogen unless you want very pungent onions. The fertilizer I recommended is a urea-based nitrogen. If you like a very pungent onion you can substitute 21-0-0 for the topdressing at 1/2lb per 50′ row.

That's all there is to it!

Following these guidelines, and with a little help from Mother Nature, you should have some large-size onions this year.

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