onions uvm extension

To ensure a good harvest, plant onions in full sun in nutrient-rich soil with good drainage. (photo: Tom Hermanns/Unsplash).

A simple staple in many cuisines and recipes, onions can be a satisfying plant to grow in the garden. While it is easy to buy them at the grocery store, fresh onions are unique in flavor and intensity.

I like to grow onions from sets, which are basically small, dried onion bulbs. Sets can be purchased in bags or by the pound from your local garden or hardware store. Try to select sets that are smaller than 3/4 inch to help prevent the plants from bolting too early.

Often you may find a few varieties of white or purple onions. Grab some of each and test out what grows or tastes better for you.

Onions are one of the first vegetables that can be planted in the spring. The best time to plant them is about 2-4 weeks before the last hard frost, or late April to early May. It is best practice to rotate the vegetable families in your beds each year, so try to plant all alliums in a different location than you did the year before.

Cabbage, beets, strawberries and lettuce are good companion plants for onions as the strong onion scent will help deter pests, while planting with peas and beans should be avoided. Onions can be planted individually throughout the garden, or planted in a group. If space is an issue, consider interplanting with dill or other herbs that won't compete for light and room. 

Onions need to be grown in full sun in nutrient-rich soil with good drainage. The pH of the soil should be between 6.2 and 6.8. You can check the pH of your soil with an over-the-counter kits, or send your soil sample to the University of Vermont Agricultural and Environmental Testing Lab (https://pss.uvm.edu/ag_testing).

Plant onion sets 1-inch deep. Depending on the expected size of the onion variety, plant the sets approximately 2-4 inches apart. 

Onions are sensitive to drought and need consistent, moist soil throughout the growing season. To check soil moisture, place your finger in the soil, about 1-inch deep. If the soil is damp, watering is not required. If the soil is dry or dusty, it is time to water.

onion plants uvm extension

Planting onions next to lettuce and other crops, such as cabbage and beets, is a beneficial move as their strong scent will help deter pests. (photo: Bonnie Kirn Donahue)

As the onions grow, the bulbs will begin to emerge from the soil. This is normal and does not require any intervention. Onions are ready to harvest when the tops begin to fall over.

When harvesting, keep the green leaves intact while gently pulling up the bulbs. Dry the onions in a warm, shaded place with plenty of airflow for a couple of weeks until the leaves and roots are dry. After curing outdoors, onions can be stored indoors in a cool, dry place with good air circulation.

Enjoy your homegrown onions in stir fries, soups, curries, main dishes, side dishes, pickled, battered, fried and more!


Bonnie Kirn Donahue is a UVM Extension Master Gardener and landscape designer from central Vermont.

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