Growing Onions

Mary Heie, Extension Master Gardener in Anoka County, October, 2014


It’s  garden clean up time and that includes harvesting and drying onions before storing.  My crop this year did not meet my expectations regarding the size of the bulbs.  Most of them are small: almost shallot sized, a couple of inches or less in diameter.  This led me to think about onions and analyze what happened this year.

There are several kinds of onions.  One kind, a perennial, is known as Egyptian “walking” onions. Sometimes they are referred to as “winter” onions. They develop little bulblets at the top of the stems.  When the tops get too heavy, they fall to the ground and the little bulbs form roots wherever they land. These onions are grown for their stems as green onions. They can be planted any time, including in the fall.  Other onions are biennials – they grow from seeds one year and finish their life cycle the following year.  But these are not winter hardy in Minnesota. There are ways to plant onion seeds indoors in the winter and have onion plants to set out in the spring.  However, it is easiest for most home gardeners to purchase onion sets (small onions without tops) or onion plants for planting in the spring.  I had planted onion sets. 

All onions need full sun (up to 14 hours) for the best success. That was the first problem.  My garden is small and I try to plant as much as possible in it.  I had planted the onions on the north side of the row of beans and tomatoes.  Of course, eventually the onions received too much shade as the other plants grew.  What was I thinking?  Onions are shallow-rooted and require constant and consistent moisture for growth.  In the early summer there was too much moisture and probably not enough later in the season.  Although soaker hoses follow the rows in the garden, I suspect that there was competition with other vegetables for the water.  The vegetable garden was weeded frequently and mulched with grass clippings.  That’s a plus for onions as they do not grow well with weeds. 

Nitrogen (N) is one of the most import nutrients that onions require.  Too much rain or irrigation can leach available nitrogen from the soil.  Phosphorus (P) and Potassium (K) are also needed.  I had worked some garden fertilizer (a standard 10-10-10) into the soil before planting, but was lax on any other applications. My onions were probably starving for food.  

Harvest onions when the tops are about half dried out and falling over.  Dig them up carefully so the bulb is not damaged. They need to be allowed to cure by drying.  Spread them out on some newspapers or in a shallow box for a few days.  After they are dry, the tops can be cut off.  If the tops are long enough, they can be braided. Store the onions in a cool, dry place.   Don’t peel off the dried skins until you are ready to use them. I decided that not all is lost: this year my onions are the perfect size to be used whole in roasted vegetable recipes and stews!

Visit these links for more information on growing onions: